Contents
viii ix
Preface Examples
2.7.5
Driv Drivin in
50 53
prec precas as pile pile
53 66
Bibliography Site investig investigatio ations ns 1.1 1.2 1.3
1.4
1.5
Walk Walk-o -ove ve
67
surv survey ey
Desk Desk stud stud Site Site inve invest stig igat atio ion: n: fiel fiel work work ia pi gs 1.3.1 Boreho hole le reco record rd 1.3.2 Bore Site Site inve invest stig igat atio io proc proced edur ur Boreho hole le logs logs 1.4.1 Bore ia pi gs 1.4.2 1.4.3 Groundwater Standa dard rd pene penetr trat atio io 1.4.4 Stan
3.1 3.2 .3
3.3.1 3.3. 3.3.
test test
3.4
11 Limestones Chalk
1.6.3
Salt Gypsum nv st ga io
.6.4
11 11 13 14 or
inin inin
Moist Moisture ure movem movement ent
81 81 81 82 82 82 82 82
si 21
4.2. 4.2.
is
ntro ntrodu du tion tion idth idth of foot footin in 2.1.1 Soft Soft spot spot 2.1.2
23 23 23
4.2.4
he st ndar ndar
ne 2.1.3 Fi cl ys verl verl in soft soft st at 2.1.4 Dept Dept of foot footin ings gs 2.1.5 Wide Widene ne rein reinfo forc rced ed stri stri foot footin ings gs
25 26
si
29
4.2. 4.2.
4.5
bs va ions ions
Ul im
Plat Plat bear bearin in
pe etra etra io
ea in
test test
Rein Reinfo forc rced ed stri stri foot footin ings gs on repl replac acem emen en gran granul ular ar fill fill
32 33 34
2.6
Pa
44 44
2.7
Piled Piled founda foundati tions ons Bore Bore pile pile 2.7.1 2.7.2
47 47 48
2.7.3
48
an pier pier foun founda dati tion on
soil soil
74 76 77 79
Bibliography
23
ound oundat at on
2.2 2.3
pa it of oh si st ss is ri utio utio
14
Sheffield Bibliography
2.
ea in erti erti
67 67 68 68 70 70
71 72
Inte Interp rpre reta tati tion on of labo labora rato tory ry test testin in Chemic ical al test test 1.5.1 Chem 1.6.1 1.6.2
Introduction Sett Settle leme ment nt in cohe cohesi sive ve soil soil onso onso id ti sett settle le
ac ti
test test
83 83 84 84 86 87 89 89 90 90 90 92
4.6.5
Bibliography
Dyna Dynami mi
pile pile form formul ul
92 93 93 93 94
Contents
viii ix
Preface Examples
2.7.5
Driv Drivin in
50 53
prec precas as pile pile
53 66
Bibliography Site investig investigatio ations ns 1.1 1.2 1.3
1.4
1.5
Walk Walk-o -ove ve
67
surv survey ey
Desk Desk stud stud Site Site inve invest stig igat atio ion: n: fiel fiel work work ia pi gs 1.3.1 Boreho hole le reco record rd 1.3.2 Bore Site Site inve invest stig igat atio io proc proced edur ur Boreho hole le logs logs 1.4.1 Bore ia pi gs 1.4.2 1.4.3 Groundwater Standa dard rd pene penetr trat atio io 1.4.4 Stan
3.1 3.2 .3
3.3.1 3.3. 3.3.
test test
3.4
11 Limestones Chalk
1.6.3
Salt Gypsum nv st ga io
.6.4
11 11 13 14 or
inin inin
Moist Moisture ure movem movement ent
81 81 81 82 82 82 82 82
si 21
4.2. 4.2.
is
ntro ntrodu du tion tion idth idth of foot footin in 2.1.1 Soft Soft spot spot 2.1.2
23 23 23
4.2.4
he st ndar ndar
ne 2.1.3 Fi cl ys verl verl in soft soft st at 2.1.4 Dept Dept of foot footin ings gs 2.1.5 Wide Widene ne rein reinfo forc rced ed stri stri foot footin ings gs
25 26
si
29
4.2. 4.2.
4.5
bs va ions ions
Ul im
Plat Plat bear bearin in
pe etra etra io
ea in
test test
Rein Reinfo forc rced ed stri stri foot footin ings gs on repl replac acem emen en gran granul ular ar fill fill
32 33 34
2.6
Pa
44 44
2.7
Piled Piled founda foundati tions ons Bore Bore pile pile 2.7.1 2.7.2
47 47 48
2.7.3
48
an pier pier foun founda dati tion on
soil soil
74 76 77 79
Bibliography
23
ound oundat at on
2.2 2.3
pa it of oh si st ss is ri utio utio
14
Sheffield Bibliography
2.
ea in erti erti
67 67 68 68 70 70
71 72
Inte Interp rpre reta tati tion on of labo labora rato tory ry test testin in Chemic ical al test test 1.5.1 Chem 1.6.1 1.6.2
Introduction Sett Settle leme ment nt in cohe cohesi sive ve soil soil onso onso id ti sett settle le
ac ti
test test
83 83 84 84 86 87 89 89 90 90 90 92
4.6.5
Bibliography
Dyna Dynami mi
pile pile form formul ul
92 93 93 93 94
Examples
together :san ca +roblems, designs [lauded [lauded are ou an e i r=minated
2.1 2.2 2.3 2.4 2.5 3.1 3.2 4.1 4.2
Stru Struct ctur ural al calc calcul ulat atio ions ns fo thre threee-st stor orey ey fiat fiat Disu Disuse se well well Bore Bore piles piles p f
p f
g o s o
Council
6.2
Stri Stri foun founda dati tion on
on clay clay soil soil
40
6.3
Fo ndat ndatio ions ns on
site site
49
6.4
Site Site inve invest stig igat atio io an foun founda dati tion on desi design gn heav heavily ily wood wooded ed site site Fo ndat ndatio io desi design gn on site site it atur atur tree tree
6.5 7.1 7.2
n g
7.3
Lied
th calc calcuumission
Page
fg
4.4 4.5 4.6 4.7 4.8
7.6 7.7
Desi Design gnin in
g r th rein reinfo forc rcem emen en in an irre irregu gula la t m
9.3 1. trees
ta en in Thic Thickn knes es of reta retain inin in wall wall Pock Pocket et-ty -type pe retai retaini ning ng wall wall yr dc Bric Bric reta retain inin in wall wall Rein Reinfo forc rced ed conc concre rete te reta retain inin in
atur atur
atur atur tree tree
129
155 ts 157 160
165 wall wall to
8.1
n,
omplete
it
it
n o e c Impr Improv ovin in mixe mixe clay clay fill fill arti artial al epth epth trea treatm tmen en of fill filled ed grou ground nd Dynami Dynami consol consolida idatio tio Foun Founda datio tions ns besi beside de exis existi ting ng buil buildi ding ng
194 196 200 205
ix
Contents Buildi Building ng in minin minin local localit ities ies
5.3 5. 5.
95 96 97 99 99 99
Shallow Shallow minewor mineworking king Dril Drilli ling ng inve invest stig igat atio ions ns tabi tabili lizi zing ng ol work workin ings gs 5.5. 5.5. Coll Collap apse se work workin ings gs ou at on
ar as
it
allo allo
ng
ti atin atin ects ects in ng id ce 5.9. 5.9. Long Longwa wall ll mini mining ng (adv (advan anci cing ng yste ystem) m) 5.9. 5.9. De igni igning ng buil buildi ding ng fo futu future re inin inin
100 100 100 101 101
7.2.3 7.2.4
7.3
5.9.7 Bibliography
in
acti acti 107 109 112
Site Site with with tree tree .1.1 .1.1
6.1.3
113
Clim Climat atic ic vari variat atio io an es tw en ee foundations Foun Founda dati tion on dept depths hs rela relate te to prop propos osed ed tree tree an shru shru plan planti ting ng
7.4
g o
ep tr
oo in
7.2. 7.2. Spli Splitt-le leve ve hous housin in Retai Retaini ning ng syst system em Cant Cantil ilev ever er wall walls: s: rein reinfo forc rced ed conc concre rete te or brick brickwo work rk 7.3. 7.3. Gabi Gabion ons, s, crib crib wall wallin ing, g, rein reinfo forc rced ed eart eart 3. te et li Desi Design gnin in reta retain inin in wall wall 7.4.1 Acti Active ve pres pressu sure re on wall wall 7.4. 7.4. Surc Surcha harg rg load loadin in 7.4. 7.4. Pass Passiv iv resi resist stan ance ce (gra (granu nula la soil soils) s) an ilev ilev ed etai etai in ls
Buildi Building ng on filled filled grou ground nd 8.1 2
121 8.
d s
Open Openca cast st coal coal work workin ings gs F f r t f 8.2. 8.2. Pile Pile foun founda dati tion on Susp Suspen ende de grou ground nd-f -flo loor or cons constr truc ucti tion on specification 8.4. 8.4. Proc Proced edur ur 8.4. 8.4. Site Site test testin in befo before re back backfi fill llin in 8.4. 8.4. Foun Founda dati tion on
oo
f g
8.4. 8.4. 8.5.1 8.5.2
d f d s Prot Pr otec ecti tion on to drai draina nage ge 6.3.3 Precau auti tion on agai agains ns clay clay heav heav 6.3.4 Prec Foun Fo unda dati tion on in gran gr anul ular ar stra st rata ta over ov erly lyin in 6.4 shri shrinka nkage ge clays clays Bibliography
rd
7.5. 7.5. Rein Reinfo forc rced ed cavi cavity ty alls alls Pocketet-typ typ walls walls 7.5.3 Pock 7. am pr in to et in ng alls alls 7.6. 7.6. yp stru struct ctur ures es tank tanked ed prot protec ecti tion on yp tr tu ai ed av ty construction Bibliography
113 119 119
8.6.1 8.6.2 8.6. 8.6. 8.6. 8.6. 8.6.5
126 127 134 136
Grou Ground ndwa wate te im ov echn echn es Dynami Dynami consolid consolidatio atio Surc Surchar harge ge loadi loading ng fs Materia Materials ls specifi specificati cation on Definitions uita uitabl bl fillma fillmate teri rial al Un uita uitabl bl ater ateria ials ls Compaction
Bibliography
tu
in
Ground Ground improv improvemen emen
th clay clay il 9.
n s
vi
g s
leve leve or
148 148
7.3. 7.3.
103 esig esig in ip mini mining ng area area Movem Mov emen en joint joint
Chan Change ge in th grou ground ndwa wate te
Vibr Vibroo-co comp mpac acti tion on tech techni niqu ques es Type of trea treatm tmen en 9.1.1 Type
148 149 150 150 150 151 152 152 152 156 156 169 169 172 174
175 177
178 179 181 181 181 182 182 182 182 182 182 183 183 183 183 183 184 184
185 186 186
Contents 9.1.3 1.
147 147 147 147 148 148 148
9.2
Enginee Engineering ring superv supervisio isio ib co pa ti ne columns 9.1. 9.1.5. 5. Foun Founda dati tion on on vibr vibroo-co corn rnpa pact ctio io ites ites Dynami Dynami consolid consolidatio atio
11 4.
11 4.
201
an
er in Toxic Toxicolo ologic gical al effect effect of
Buil Buildi ding ng up to exis existi ting ng buil buildi ding ng 11 10.3 10.3 Unde Underp rpin inni ning ng m a d p Case Case stud stud
Case Case stud stud
10.1 10.1
205 212
Inve Inve tiga tigati tion on an unde underp rpin inni ning ng etac etac ed ou ad
11
ILl
Conta Contamin minate ate
226 227
lan
229
Cont Contam amin inat ated ed site site
11.3 Risk Risk assess assessme ment nt 11.4 11.4 Indu Indust stri rial al proc proces esse se
11.5.2
ll ites ites ig ti Gas monitor monitoring ing bo xi xter xterna na meas measur ures es
11.6 11.6.1 .1 ocal ocal geol geolog ogic ical al stud stud 11.6.2 tr al to he 11.6.3 Mining Mining investig investigatio atio 11.6 11.6.4 .4 Site Site reco reconn nnai aiss ssan ance ce 11.7 11.7 Site Site inve invest stig igat atio io
10.2 10.2
10.4 Shoring Bibliography
an
11.5 11.5.4 .4
175 177 178 178 178 179
ailw ailw
235 236 236 236 236 236
Preloa oadi ding ng usin usin surc surcha harg rg mate materi rial al 9.3 Prel Improv ovin in soil soil by chem chemic ical al or grou grou in ecti ection on 9.4 Impr Bibliography 11.4 11.4.1 .1
172 174
ap et
148 150 150 150 151 152 152 152 156 156 169 169
235 235 235
11.7.2
Boreholes ti ic as 11.7 11.7 Chem Chemic ical al anal analys ysis is af ty 11 7. Conc Conclu lusi sion on Case Case stud stud 11.1 11.1
te
238 239 240 241 241 242 244 244 244 244 244 245 245 245 245 245 245 245 246 248
229 230 251
181 181 181 182 182 182 182 182 182 182 183 183 183 183 183 184 184
185 186 186 187
vi
Chapter Site investigations
urch te er ta is et ther ar an hazard on or belo th it whic coul re ul in expensive house foundations. Re ember: yo pa fo site investigatio hether yo er en inadequate site investigatio coul be at leas as expensive, ch an av ie out. he builde should vi it th site an ak enquiries. he
CH ICAL
UE
IONNAIRE
Lan.e, Y c w k , 1.
Give descriptio
RV te
P~A.cuvJ.
of site
2. Give directio an gradient of slopes Ar ther an indication of hill creep? 3. Presence of trees, streams, marshy area etc.
esti ti
S A & . ~Aetue,{
Y.oo.
trenches, nearby quarries etc. 5 . I s t h r e a n i nd ic at io n o f f i present? 6.
st before purchasing th land ot al ground hazard requir engineer-designe foundations. Sometime it ma just be si pl ca of placin th stri footings deeper into firmer in
th
Standard en th NH te isio ch en builde should be able to make However, th builde us recogniz when specialist need to be consulted. Site investigatio should be spli up into thre sections
asthe it e e p re vi ou sl y developed? Give an indication dept an type of existing foundations.
of
a v y o t ak e r ou n e ve l n d obtained th location of borehole an trial pits 9.
r e t he r n ea r b ui ld in gs ? A n sign of cracking An informatio foundations of suc buildings Isth
it
ni
on
ar a?
11. Have yo obtained al informatio on soil conditions from th tria pits Dept an descriptio of strata Leve to the groundwater 12. Have yo obtained shea strength usin th shea vane
es ti esti ti ld always be carrie out. Th Technica Questionnair Survey aide-memoire when carryin ou th walk-over survey
13 What sample
in
Fig. 1.
ea
e in g
re ny ol as nt r e e nt ? I f so give detail of extent an depth.
ir
walk-ove survey (ver important) an initia deskto tudy fiel investigations usin tria pits or boreholes.
ti
te
CAJ'H'.(U'"
ximately m. If ther ar hazardou ground conditions th builde ma
th
el
HE
have been taken?
14 Have ground wate sample been taken? From whic pits
Technica questionnaire survey sheet.
copoe o f s '
s£.
Sit investigations
investigatio by observin th site topography Informatio ca be gleane fr loca inhabitant an people workin in th area i.e. fo tatutory auth rities such as gas, wate an electricity. An evidence of likely ground instabilit should be noted, such as th following.
Hummock ridged groun indicates hill cree an possible unstable slope Sof strata with high wate tabl
Surfac depression
Existing ve etatio an tree Railwa cuttin
(Fig 1.2) Slop instability hill creep (Fig. 1.3) Cla desiccation Expose strata (Fig 1.4)
Existing structures
bell pits (Fig.'1.5) Record an visibl damage
Hummocky terraced ground
Groundwater, spring etc. urface holl ws
Reed bullrushes etc. Manholes
required? Sign of landslip Coul construction prob lem arise? lu in chal (Fig 1.6)
Fig. 1.
Slop stability.
Always examin
~.
fo railways et
Fig. 1.
Coal outcrops Surfac spoil heaps
workings enerally indicate peat or we ground watercourse
Existing dwelling Surfac cracking ap in existing houses
cellars Indicative of soils plasticity
Backfilled bell pits or mine shafts
mineshaf (Fig 1.7) ee Lane? Construction proble s; expensive land drainage
ed
Fig. 1.5 Bell pits
it
Swallow hol
table
Hollows arising fro solution nc
,_/:":~
-'_"
hi involves collecting as much info mation as possible abou th site Source includ geological maps Ordnance
(
-
~-------Fig. 1.
_ .= = = = = - _ _
1 -
Solution features
i.&jCrown hol resultin from collapse strata abov ol mine workings
Fig. 1.
Crow holes.
Shallo
mine workings
Larg gaps betwee existing building ma be as result of main drainage in shafts or majo services Chec on ol rdnanc Survey plans.
Fig. 1.
Gaps in existing development.
Desk stud
'.
ap ic em al to mining record an previous it investigations fo th it ad ce it th at in
ol quarries ol landslips or depres ions caused by ol mine shafts or infilled quarries. .M in lway is
sources.
togethe with mine shaft records Britis Rail here railwa tunnel pa se belo th site construction shafts ay be present. Detail of thes ay be held by Britis Rail engineers. istric ineral valuer he have useful informatio on ol mines quarrie an mineral workings.
in at ld in an ol watercourses Evidence of previous building
development. eo ca ir an iv io in shafts coal outcrops an trat succession (the differen levels an type of strata). Aerial photograph give valuable informatio relating to previous tree or hedges on th site he ca al reveal
DESK STUD
CHECKLIS
1. Site topography salien vegetation an drainage (a Ar ther an prings ponds, or atercour es ea te (b Isth site steepl sloping? c) th an ev ee site? 2. Ground conditions othe minerals? (b ha is th geological trat succes io belo th site c) la in asti it (d Isther an evidence ofslope instability?
3. Proposed housin (a ha type ofdevelopmen isintended? (b ha foundation load ar expected in at eq ab specia foundation to be designed e.g. piling dewatering? 4. Identification of ground conditions Byconsulting eo ca ec an lo io the surface (a Type of drif material e.g. sands, clays,shales indicate maps.
on borehole record an geological
ic au glacial valleys
strengths?
'c.
co lt io in loca authorit building inspectors fo informatio on an en te lt it al th tu ic undertakings in re pect of an existing services whic ay be on th site to be investigated
in to
ie
Fo low-rise housin (two to thre storeys) th foundations
Site investigations carrie ou in th summer months ma no
0kN
Octobe to Februar periods. ay at to th ic ty inde of th clay need to be determined especially if ther
in
tr
ti
tl
than 25 mm. In general, it is only when soft alluvium peat strata an le co et le en ac unacceptable magnitudes lluvia soils, peat an glacia head deposits ofte have considerable variations in stratu thicknes over relatively shor distances. Peat beds ar ofte formations. ands gravel an rock trat usuall provid excellen bearin capacities with settlement taking plac over shor timescale. Th effect of groundwate on sand an gravel is to reduce th ground bearin capacity an allowanc should be made fo variations likely becaus of seasonal variations
This informatio is required in orde that foundation ca be formerly NHBC Practice Note 3. Informatio abou th site an it underlying stabilit ma construction progra e: avoiding long terrac blocks in mining areas, provisio of public open spac in an no-build zones, an providin ovemen oint at change in storey heights fo example. ti as la plan show no-build zone at th high wall batter planes th
Sit investigations 1. .2
This should indicat th followin informatio (Fig 1.9)
economically. 1.
Borehole record
SITE NVESTI ATIO
roun leve at th bore ol positi n. hi is very import ta it en tt in es igation is bein done to assess th site stabilit fo possible shallo coal workings it is essentia that ground levels ar know if accurate trik line of th seam ar to be ra n. Depths an descriptio of th variou strata encountered. epth of an ater entrie an th fina standing level. Piezometer readings if applicable ch io am te ta U(samples obtaine undisturbed from th borehole)
FIEL
Fo low-rise housin it is enerally considered that impl mining ground conditions When excavated, they should be deep enough to confir that th strata belo th proposed foundation leve remain competen an adequate fo at leas furthe et belo tandard- idth footin of 60 Th inimum dept of th tria pits should rang ro 2. to er ib th ld le proposed dwellings. If th position of dwelling ha no been finalize then th tria pits houl be accurately locate fo th site survey If an adequate formatio dept is no encountere within th ,reach of mechanical excavato then larger machin in-situ fiel test ar needed then shel an auge borehole will need to be drilled. If poor ground conditions ar eviden during th drilling of borehole then th borehole should be take well belo an suitable strata whic ma have to suppor piles.
Figure 1. show th strata variations
1.4
SITE INVESTIGATION PROCEDURE
ti
clays we loos sands; ti
trat in
ir
tria
th th
orehol
Thes sh
cc
an
ar in BS 1377(BSI 1990).
og
th ground conditions only at th po itio of th
correlate bu th accurac cannot be guaranteed.
hese enable soil conditions to
sands; ch at en fina dept at whic it stabilized; th al co
ed
ai in el procedures laid do
1.4.
ll in at ld in th tr it together it site la showin an accurate location of th tria pits (Fig 1.8)
tandar ke sy bols fo annotating
examined in mo
tr il useful indicator of th soil strengths.
detail id
in 1.4.
compaction). information should be taken. en te ts th shea values fo clay strata to be determined Thes values when double will give an approximat allowabl bearin pressure allowing fo factor of safety of 3.0.
Groundwate levels ca vary becaus of seasonal effect an ll ce ti ca em ar casing ma seal of seepag into th borehole
1.4.
Standard penetratio
ar al
t, li it as ic index, soluble sulphate an pH (acidity) le is ld topsoil, vegetation, organi refuse rags metal, timber po sibl th percentage organi atte uc as ti be should be indicated.
roundwater
ly co es
test
ta ls
an an
Chapte fo descriptio of th standard penetratio test.) ec if ty ta cc values especially in filled strata containing larg stones th result ly as id es th strength. Tables iv te soil strength base on SP values
Site investigatio
f.
TRIAL PIT RECORD
1.9).
SITE SURVEY
ate:
ndlevel ar tf' be draw hug level.
Client:
eM
Site Address:
Rowa./)
Location:
Pho..se.
From
samples ole).
To
(BUILDER 5) aa
AvenuQ.,
LTD
York.sLUre
Descriptio
Key
of strata
fY cOl"1prrsi':_9 loose lumps 0( conc~!:.e, soil r n. g Y le l" lT s t::imber ~I-o()es C V l
0·30
': .nnotating 0·30
JACKSON
mADE
,.70
GROUND
modera..Wj
cICl
Brrck::
accordance samples.
o·gO
bncks,
c.om ri5itt_
COfr)pQ.d:
Foo/;~(Js
eACOVll
firM.
+«ed
f-
I-
brown
fine to .r wiHt. sfor11l..~·
d~
1qql
MARCH
investipossible
No.
LT
ver import _!
procedur
b r b W )
to
dowll
r-r-
osition of the .s
T'tlAD to
2'10
"7
rM
bl~k o_
more detail ty the .s provide
li
J'
'2.·60
~'IO
'6
~'70
'].'70
"3.0"0
,.
6~OOIllD
MedioM.
o..s;hes
Sop-
fo
tV~
s~
c.Df'l1pri.s.iI18
8~
(oIe.ckuM.
sil.l-j
/;0
~v
wiHt .so..IId . s . f - O l \ . . e .
E,.,d
!-rial
Jk
c.J~
clark:
CLAY. CLAY
Sto.tt
pCl.j{1AlUl
l:o $~iFf r w u l W r 1 '\ .
FirM.
~·ao
sJ-ot'1l.~
£li1
FirM..
FirM. MlLdioM wJ-i.l friCLble
brow"
Ioro .....
CUlY
R C A . , 9 V W ! .1 \ t-s '-
pi/-
effects and te
'-
,_ f--
ar
ff-
.tram bu ca
ey an .trata. (See etration test.) values
Test results, wate observations an remark
Slot.Al (Sulk.
V~
erow"ld so...mpl.es
w~.fU"
~keA
~esl- r e a . . c f . v 1
th ground at id Fig. 1. Typica tria pi log.
"'a~S c:U-
ai:
a.1:
O·75t\.f.
2·20""
2'OOM
'k I'SOM '2·50",,-
FroM.
Iodlk~I€.
Sit investigations IT Sit
BOREHOLE
Avenue.
V
Address:
DATE
NUMBER
Location
Wa.keFie1d., BORING
Yorks.
Type of Drilling
SAMPLING
IN
Depth (m)
Nt ROD.
0·00
Level (m)
10Q-o
D es cr ip ti o
f'i1o.de.
diUM browl\.
...=-
.....
..... .....
..... ..
..... ....... .. ..... ....
.....
r-
.... .... .... .... ....
SQ.lldj
CLAY
par
er~-
I...I:Jk.oI- fo ~dill»1 l.ull'l ~d i7Le t-
f1a.53j.
(lro..i.ne
brc11.Jl/l-
sANO~ONE:
Oo:.a. '$10 nal: ~hin b
C l ~ o f ~B~
f'''4
..... .... ..... ..... ..... .. .....
WoJ-w
'''jress
Bla.c.k Ash
Ir s.~
LI
4-'cm
o f s tr at a
ADD
~"-
rE
S TR AT A
Key
l2S22 2.·0
P€("cvs$./ve
Qol-ru-~
R EC OR D
Type NYC
De~th (m
BOREHOLE
RECORD
q·oo
'"
....
.... -" ....
\0'00
MediUM fo
siJ1-s I-oi\e
Er~-bro"'A
DarK
U"o/\ Sh~..t\ed !;~ ~tJl).sTONE wiHI.
S~i.
iA!:erb
Cicled
ba.t1dU!~
r- ?"50 lool\.
1===
1?1cu:~
t===
ere3
to cia..rk:
MediUM
i===
l"v\uOSTONE
u.icHt
c=J!:j
-brow!\..
sVia.A~
"'-f-eree.Clde..d b:v1ds.
.sl1c:d.e
.,
t=== 17·00
Moo.il/Vl
i===
r-
i===
r=s=
'2.1·0
Remark
an
groundwate
Grool\ wal-er
Fig. 1.9 T yp ic a
o re ho l
og
observations
i¥l~re.ss
~·OM.
bla.c.k uJi.I-~
to dark: (rE?j evld fodl-.j s V J ~ rl4.ud.sJoAe
bq_"
co~ Borehol-e
Site investigatio SOILS
I:.:.:
1=--=-==1
SEDIMENTARY ROCKS
Mad ground
Chalk
Topsoil
Limestone
Boulders and cobble
Conglomerate
Gravels
Breccia
Sands
1·······
Sandstone
Silts
I:::
Siltstone
.....
Clay
Mudstone
Peat
Shale
Note Composit soil type will be identified by combined symbol e.g.
Coal
Pyroclastic (volcanic ash
ilty sand
Gypsum. Rocksalt etc.
METAMORPHIC ROCKS
IGNEOUS ROCK
~tt+tl '_·+~L·+ ...
Fine-grained
Fig. 1.10 Ke to soil sy bols in tria pi logs
"V.JV V.vV
procedur
Sit investigations
AB RA
ESUL S:
Bulk sample
disturbe
Cohesion
/m
iv
YMBO Solubl
sulphate conten
ur
di
oh
in
California
Bearin
Rati
Ja sample
disturbe
atural moistu
ne
Liquid limi (%)
c' CBR
RY
bo
or
kN
ia Wate
densit
/300mm) id
ka
it
on
sa pl conten
(%)
Plasti limi (%) Bulk densit kg/m
JkN)
mv
le
nd
kg/m
ngle of shea in
la ti
Effectiv
Soil strengths.
angl
esistanc
of hearin
Ty
degrees) re istanc
in
(degrees
it M a i mu m
Table
1.1.
Rocks
lu
in Nvalue
sandstones
(kN/m2)
S ch is t Very stif
10-20 Firm
40-75
4-10
Soft
20-40
2--4
V er y s of t
<20
<2
le
3200 to
2200
sandstones Clay shales ar
s ol i
1100 c ha l
650
T hi nl y
e d e d l i e st o e s
H ea vi l
s h t te r
an
s an ds t n e
r oc k
Non-cohesive soils"
fo
Couistency
Nvalue
Very dens
50 30-50
Dense e di u
n d s la te s
20
1.2.
10 00
condition 4300
strength
Table
s af e b e r i
capacity
(kN/m
e ns e o r c om p c t
gravel-san gravel-san
220--430
110-220
mixtures if
4-10
Very loos
Submerged
mixtures
10-30
Loose
Dry t,
L o s e u ni f r m s an d
<4
Cohesive soils" ti
Table 1.3. F ie l
a ss es sm en t
w it h
s oi l s tr en gt h
s ha l
s tr uc tu r
430-650
ti
220--430 la
Consistency shea
s oi l
la
strength
110-220
il
55-110 55-nil
(kN/m2) e at s a n
ma
b e a ss es se d
g ro un d a ft e
i ns pe ct io n 10
hand y l pressure 40-80
'Dry' el th as C oh es iv e s oi l a r s us ce pt ib l t o l on g- le o b e d et er mi ne d a ft e i nv es ti ga ti o
be
es
an
c on so li da ti o
pressure 80-150 Very stif
Indented by thumbnai
150-300
nd on
o i thumbnail
no
he la
nd in
I/Iu
iv
th
pa
I / I u . With saturate
Interpretation
compressio strength in ax an al carrie ou usin th triaxial co pression apparatu an is know as th slow te t. Th approximat consistenc of clay soil ca assessed in th fiel by handling th sample Tabl 1. list th criteria in iv es ai shear strength. variou soils; these figure should only
used as guide.
of laboratory testin
plasticity inde ca be plotte on th standard Ca agrand plasticity char (Fig 1.12 to confir th clay classification th bulk amples ar sand or gravel ixtures, gradin istr io ts lo ed ch whic indicate whic zone th material fall into aterials bu they ar of particular valu when considerin ground improvemen techniques such as vibro-compaction, dewaterin or groutin operations.
egrees)
TESTING
capacity
;0
Submerged
220-320 110-220
:0 :0
110-220 55-110
Once th result of the laborator tests are determine the can used in conjunctio with field tests to determine th strength ta te th eh logs it is possible to buil up pictur of th st atificatio of soils belo the foundations. report carrie ou in accordance with BS 5930 (BSI 1981 an tested in accordance with BS 1377 (BSI 1990). Generally, suitable 10 mm sample ar subjecte to quic undraine triaxial co pression testin usin thre peci mrn long take from each sa ple. Th sample ar tested unde latera pressure of 70 14 an 210 kN/m at constant rate of strain of 2% pe minute Th result of thes tests, comprising shea strength parameters ap co te ct 1 / > , natural moisture contents fiel dr densit an Atterber limits ca the be determined Tabl 1. illustrate th result of severa quic undraine comp'llessiontests When th angles of internal friction ar diagrams ar draw (Fig 1.11). From thes values th shea
te al whethe ther ar an
ie ut ch te ubstance in th ground whic coul
te ists th la if at sulphates in soil an groundwater. ER Digest 36 (BRE 1991 give variou reco menti ab cr es sulphate attack Thes ar listed in able 1.7.In addition to cement ratios th concrete should be dense, well cure an of
concret with en
lo
Ta
ic ti
workability ie
lp
2:1
S03 (%)
bearin capacities ca then be determined usin th appropriat factors of safety.
aqueou (g/litre)
In groundwate
extrac
>2.0
Ta
(g/litre)
<0.30 0.30-1.20 1.20-2.50 2.50-5.0 5.
;0 'l
it
5.60
Borehole no.
whic fallc":i?toh higher classification Fo example, if si (degrees)
es than 90 mm IS than 90 mm
cohesion Wit saturated th apparent
0.50' 1.50' 2.0
45 20 51
0.30 0.80
46 50 112
lAO'
an ar henc non-aggressive whil th othe four fall into 24
22 18
2.050 2.218 2.103 2.035 2.090
categor of risk
acidity classificatio fo various pH values. An foundations
10
2.30' 'Indicates test result used toproduce th Mohr stress circle in Fig. 1.11
durability of th concrete used belo
ground
Sit investigation Table
1.7. R eq ui r m e t s
lp te
f o w el l
il C on c n tr at io n
cast-in-situ concrete
o m a ct e in
140-450
lp te
s ul p a t
an
m a n es iu m
2: water/soil extraction
a xi m
(%)
S04
f re e
water/cement Mg
S04
rati
Mg
S04
Note
A-L A-G I-L
0.65
330 280 300
0.50 0.55 0.55
320 340
0.50 0.50
If
on
<1.0
basis
0.45
2:1 >1.0
360
0.45
la plus surfac
protection
>1.2
>6.7
lu C em e c on te nt s r el at e t o n o i na l m a i mu m i z a g r e a te . In orde to maintain th cement conten of th mortar fraction at simila values th minimu cement contents give should be increase by 40 kg/m fo 10mm nomina maximu size aggregat an ma be decrease by 30 kglm f o m m o mi na l m a i mu m s iz e a g r e a t a s e sc ri be d i n T a l e o f B S 5 32 8 a r I . N ot e T h m in im u a lu e r e u ir e i n B S 8 11 0 9 8 a n B S 5 32 8 a r I : 1 99 0 i s 2 7 g /m ! f o u nr ei nf or c s tr u t ur a o nc re t i n c on ta c w it h n o aggressive soil minimu cement conten of 30 kg/m (B 8110 an maximu free water/cement rati of 0.60 is required fo reinforced concrete minimu cement conten of 22 kg/m an maximu free water/cement rati of 0.80 is permissibl fo C2 grad concrete when usin unreinforce stri foundation an trench fill fo low-rise building in Clas I. Source Base on BRE Digest 363, July 1991 N ot e
Table
1.8 pH Values
C la ss if ic at i
of
pH valu
ph
acidity
>6.0 5.0-6.0 3.50-5.0 3.50
Negligible Moderate High V er y Table
ig
1.9.
on
or
ve ordina
io
of ul
Po tlan
ic ti
bl
1.
cement
to
te
r an g (a) (b)
7.0-6.5 6.5-5.0
Attac probabl unlikel Slight attack probable
(c)
5.0-4.50
Appreciabl
BS 882 (BS! 1973) 330 kg/m.',
0.50
io
attack probabl
BS 882. 370 kg/m
0.45 (d)
<4.50
Severe attack probabl
0.45.
it
ld to
ad
10
w it h o r i na r
o rt la n
c em e t s
ll
te
l at e
Solution features
TRIAXIAL COMPRESSION TES RESULT (QUIC UNDRAINED)
7'+0 free
Client:
ment rati If"
Location:
rs.c.
D~ H1 Q. 2. OescripliM: .....(~.~()!.e. N .o . ohe;(9.t.\. 4-5 kNj",~ A~I:e. ... . f . . S . h ~ ~
.65
SCMcl(J < tJ s1 ~ .r q
/~
':t.~...
.55
'.45
1.45
.ar values,
il
with nonf~-~ed :<
/he using
he
th
',_u classes. 1. relates
rc
ur, and if .d cement
1.6
SOLUTION FEATURES
e rv i u s
vith
:8 Okg/m
ected iigh
in th
1 .6 .
on
11
Site investigations TRIAXIAL COMPRESSION TES RESULT (QUIC UNDRAINED) JO
574-0
N°
......... .......... .......
.J"'..~'.
Ave.
LeJZ.ds
Location:
.(_<:JIIS~(uC;hQ!'\. L k : ! . .
....................................................................
27·j·q2
Date: __
...
......... ..........................
......... - . . .. . . . . .. . .. .
OepH1.. L.lI-OM.. ...... Oes.cflf ll ';J,... ~N/t'iI'2 At1~le cf s.~(~ A p p a . ( "e J l . r . . .P?~:1011.
l3ore./tJolt:. N °
$hFf
....... ...........
-SOJ'd.j d.~
rl2s(sfr:AAaz~
..I-
L...--
f..-- f..-CD
::
II
II
c: c:
'\
!II
I)
'K>
60
o(2. V1o~g_.....
~o 10
120
1'10
2:20
2't)
1&
Applied normal stress (kN/r-n2
' ? ' . . . . .. . . .. .J)epltL...... ..
0~ ....Q e~ip
A1j1e
! : :- N / M
~.~1t
iN'
_./'
Gre.:j cI~eJ
sJ.-.'l:-.I~...
.~0V···Ra.S(~hlt)~
O~ ......
hQI
"-.
I----'""
-:
. . - - P<
r-
!II
U; in
Ol
'f s:
,. 2D
40
{,O
fa>
'10
Applie
.,(0
2OC>
220
normal stress (kN/m2
Fig. 1.11 continued.
soluti n. Howe er soluti pi in an sw ll oles ar ofte foun in chal deposits Wher chal mining ha take
deposit ar relatively shallow. Swallo hole an sink-holes in carbonat rock strata ca
es arch
12
th av il bl
ge lo ical
ap is recommen ed
investigation.
this investigatio
reveal unstable strata it
sp carbonat strata stil intact it is generall pruden to provid stif raft foundation chalk.
Solution features
60
0~«,.
t~
50 ..
40
~«,.V
CH Ql
-:
,~'V
-c
-:
.5
Z.
30
'0
CI
-: CL
SIC
v'"
. 50
90
80
60
Liquid limi (%
Fig. 1.12 Casagrande plasticity char (for ke to abbreviation se Tabl 3.6)
100
'f
:g
Material: Supplier an source Submitte by Location:
Fi4 5 ~ . s c J > d In sib« Cli2nJ;
B ri ti s
No. 0 0 0 0
TP~
'"
O 0
., "'''' " " ' " '"
S ta nd a r
s ie v e s iz e ins
~~;!~
r-,
00
90
90
80
80
70
70
60
60
30
30
20
20
10
1--'"' Clay
Sill
Fine
0.002
Sand
Coarse
Medium 0.02
Fine .06
Medium
Gravel
Coarse
0.2
Medium
Fine 2.0
Coarse
.0
Particle siz (mm
Fig. 1.13 Particle size distribution chart.
Sa
md grouting unstable nt to provid
ha risi
ro
brin
xtra tion
er
ot result
jo
subsiden
unpr ic bl
13
Site investigations .6
proble in th future From th statistica evidence availabl it appear that on
sink-hol an larg ca er ca therefor evelop in thic be s, es eciall wh wate is ominan factor Th os significan area ar in Ripo in Yorkshir an th surround be
recorded al ng th
eologi al Survey
ut ro
of th
ps
ed within
here is evidence that sh ws that
Investigat to prov th adequacy of t h p oi nt s o f structura suppor
lo of
is co si ered ru en to ro id stif ra foundation in th flounderin area designate by th Britis Geological Survey Ol subsidence hollow have ofte been filled with organi to us pile raft with th pile take belo th gypsum
Scop of hazard cannot be fully define
assessment (geophysics, trial pitting probing, boring or drilling) L~I~e~e~~~
...-----..___--, Design and construct standard foundations (subject to normal performance criteria)
Design and construct special foundations (address any residual hazard for external areas and services)
Fig. 1.14 Decision flowchar fo sites on chal (Edmonds an Kirkwood 1989).
Investigatio
or er
inin
INTRODUCTION
site Sheffiel
shafts an spoi resultin from ironston workings coul also be presen on th site ti
se
lo
rtle oa isshow in Fi LI5. Preliminar enquirie with Britis Coal mining surveyor av re eale that ther ma unre orde mi shafts an ossi le shallo in wo ki er ar th site Ot er
14
to outlin
th
geol gical,
recommendation
as to th need fo
workings beneat
th site
eote hnical an
as
borehole investigatio
Case stud 1.
could be
it lauons in th gical Survey. th organic area
.1
(contd.)
RESEARCH SOURCE In co piling this report we have examined informatio an record an made enquirie from th followin sources: quarters Burton upon rent to examin th shaf regi te held in th archives
psum.
Trent; ce ey 190 edition;
ty
es
ti
Survey at Keyworth. Nottingham;
,scould also las mining opers This ical an pa iort
should
investigation -tallow coal ig 1.15 Case stud 1.1: site location an la out.
.15
Site investigations
(cantd.) Sheffiel City Technica Services Dept 6, Mi in Record Office at Ra mars ot er am Sout Yorkshire;
London; 8. Minera Valuer District Offices; Sheffield.
SITE GEOLOG Th 1: 05
scal
unty Series eologica
ap NZ28 SE st th site to be overlain ep sits boul er clay of lacial origin Th thic ness thes rift de osit is ot re or ed on th ge lo ical maps ut fr informatio glea ed fr
Coal
Silkstone roc
Coal Sandstone Silkston
coal
Sandstone Sandstone
:::::::8:,:;;:;;
..................
Sandstone Coal Sandstone
Sandstone Whinmoo coal PF
Coal
Fig. 1.16 Case stud 1.1: generalize
16
vertical sectio of strata belo
th superficia deposits Unlabelled area ar shales or mudstones.
Case stud 1.
Ca
stud
1.1
(contd.)
previous site investigations in th
site locality th
oulder
re Th ol
N Z2 8 most of
existin surfacelevels. se
to
recorded
19
site
ri
ib ty overlain
re
ithi
th
th
site
oundaries. Ther
re
Description of strata
Bind
._-------
~Brassband
_-
disused.A loca shaf isnoted to have
sh
in
ig 1.16
1.17 ta
th
Th
fe
Colliery shaft records
Britis Geologica Survey of Mining Term
Imperfectl laminated MUDSTONES o r n y f in e graine roc
Iro pyrite
Dirt Silkstone coa
Sof shaley material interbedde with coal
Spavin
Seateart coarse clay or udston with rootlets
~::~~:::::::::::;::::::: H ~~~~E EE ~~~[E ::::::::::::::::::: :: .....................
oundar se
Silkstone coa
.....................
..................... .....................
in
it
result of ironston extraction
-
ra
is
deposits of colliery spoil. In addition ther ma
ackfille pits on site as
oundar of th site Th
th iron orksand is no
colliery spoi heap
Su
plan showthe Thorncliff Iron orks to
clos to th northern to
fglacia eaned fro
ic
rdnanc
Strongstone
Sandstone
..
:: ::::::::::::::::::: ::;:::;:::::::::::: :: ...................
..
meso
Fig. 1.17 Case stud 1.1:vertica sectio of strata at Thomcliffe colliery
17
Site investigations
1.1
SOLI
(contd.)
GEOLOG siltstones an
mudstone with interspace
coal an
fireclay
Th pu lished geological maps show that th drif measures
horizons. Severa collierie existed clos to th site, notably
ar underlai
th
Middle an
ower
oa Measur strata of
Th
if
iery ab
(rial
(3
.5
Pit::
Bcvlder
2·7M
SOIL
Sa d4
to SOil
CLAY
5'O~
C~
"'ILL..:
..L:
'5~:
18
as stud
o..sk
Loose
CLAY:
Fig. 1.18
CI/ld ask fill
L-aose
.1 tria pit
80vklu
cia.LL darll
$1itJ~
m
brOL
uq..
sl1(f
5CU1~
to fill. OJ:ove daN< brow/!. V€(3 sf-iff;
Mai5t-, s " f P iM . e. c i d u e
BuLl:
cks
PatK
fi"oM.
S2.
bride
fJ
il
o. 51
as
si e.
Case stud 1.
as
i:
stud
1.1
(contd.) hinmoo coal seam in excess 40m elow th site Othe wo ka le coal ea ar th Hard Be coal ea (Ganister) th Coking coal ea an th Po Clay coal ea owever it is th am av in th
dstones,
fireclay .te notably (,{the site
th Thomcliffe Iron Works.
Tri-ol
Pi
C.I~
FILL
eLA Y:
sa.Yl~
dark
c~
Baolrkr
shff
browll.
wiHt. ahundcutt- 8 ( a . J . I e 1
S'f1. T~
Top~aiL: FILL cLAY
SCU1~
louse 6aulckr
EPpsoil
95 aj
w(Jh
as
ist-ore: s r- vf f
rnail5r
Fig. 1.19 Case stud 1.1:trial pi logs 53 an 54
19
Site investigations
coritd. past then an surfac subsidence associated with th workings will have long sinc ceased Britis Coal have stated in thei
theref considered that he Silkston seam will be at su epth el th site th here will su fi ie rock co er over any possible workings.
to
TopsoiL
~====================~£
1\-~_~)5M
2·30~
and:
SOIL
op5O"i
8~
Lerose
CLAY
BcrokW- c..~ sl-iff wiJ-h. 8rcweLs Q.¥IcL frOof:J~ts
Fig. 1.20 Ca
SCU1~
FILL
ver~
tudy 1.1:tr al it og S5 an S6
4-
d~
(lJ'"fc:;{
o...sk
abUllda(rt
Bibliography
Geologica faults
l' rock cove
Th
tria
it in
ti
ti
to
.5
iery
traversed by numerous geological faults which hav resulte in localizedvariations in th stratification of th coal seam
underlai
in re
thicknes ofboulde clayrecorde in th tria pits was3.0 m.
rd to th ir
th
th th
it
re
ip
natura
ro
ul er cl ys Th
aximum
Ther ma be othe area of th site whic ar overlain by te investigation.
possibleold workings.
Th tria
it record ar incl de in th ap endi to this
report (se Fig U8-l.20).
SITE HISTOR Th variou edition of th Ordnance Survey County Series were examined. Th
1850and 190 publication record the
position of the ol Thorncliffe Collier northeast of th site, an th Thorncliff Iro Works Th
19
Ordnance plan show severa ironston pits on
th site nd
CONCLUSION
ai shaf in th
orth es co
r.
AN
RECOMMENDATION
it
it
variabl in their thickness an lateral extent. Thes deposit ar
en rall natura
show to
ulde clay
ut
arts of th site re
overlain by approximatel 1.
thicknes of
colliery spoi an ironston minerals Thes fill coul resul of bell pit working fo ironstone. in
th
th
re
th 'sit
rl in
ir
tl
tura
oulder clay it is reco mended that standard widt regraded.
foundati
should
reinforc
it
stri
no inal la er
mesh typ B283 to an bottom.
PAST
ININ
here colliery spoi is evident, fo ndations
CTIVIT
take
Th available record show that coalminin ha taken plac th th
it in
ra
in
th
th
6m
elow th
into th
natura boulde clay
Though th solubl sulphate content of th collier spoil aswithin th Clas ix
rang it isrecom ende that
dopted
in to th lo
Clas
pH valu s.Al
mortar below ground should use sulphate-resistin cement.
il as
ow
inimum distance of30 mm
concrete
It et od in th
fo
il need to
ro ma
ut it isconsidered that they pr se
riskto stability on this site
re
Researche of mine record an topographical plan have ti
tr
ti
id
re
ks th
inio
th
th
il
is at
to
th workings within thes seam
ould no presen
source of
potential surfac instability excavato to carr ou slit trenchin Detail
re
rd
th
unde ou supervision. ist; it
il re
ir
cappin of at rockhead. Coalmining ha ceased in th locality, th main collieries having ee
closed Th
possibility of future undergroun
discounted.
It is therefor it
trip re
recommende that excavation during th in
shafts presen on th
to
re th re
re
site Should an
th
ncounter
in th
local British Coa mining surveyo should be informed.
It is reco
nded that th ol
rockhead level. Should th dept th shaf infill should
ir haft
ca pe of at
to rockhead
excessiv
groute down to rockhead prio to
capping at the surface.
BIBLIOGRAPHY BR (1991) BREDigest 363: Concrete in sulphate-bearing soil and groundwater, BuildingResearc Establishment BSI (1992) BS 882: Part 2. Specificatio fo aggregates from natural source for concrete, BritishStandardsInstitution.
BSI(1999) BS5930: Code of practice fo site investigations, British StandardsInstitution. BSI (1986) BS 8004: foundations, BritishStandardsInstitution.
Sit investigation in purposes, Britis Standards Institution. Ed onds C. an irkwood, J.P. (1989) uggested approach to ground investigation and the determinatio of suitable substructure solution fo site underlai by chalk. Proc International Chal Symposium, pape 12 Thomas Telford, London Joyce, M.D. (1980) Site Investigation Practice E. F.N. Spon London.
NHBC (1977) NHBC Foundation Manual Preventing Foundatio Failures in Ne Buildings, Nationa House-Building Council, NHBC Standards Chapte 4.1) London (now ewritten Tomlinson, M.J. (1980) Foundatio Design an Construction, 4th edn Pitman
i n o F o u n d a ti o n
Instruction,
Chapter
4th
2.
INTRODUCTION
allowabl settle ents Thes footings ca be unreinforced except when building in mining area ex
suitable fo th site conditions ca be established. he most simple foundation fo low-rise dwelling is stri footin or trenchfill concrete Generally, in good strata construction is straightforwar operatio bu in some situations wher hazardous ground conditions ar encountere specia care must ak ch te in ou is ia ca is needed an offers some practica advice on economic design and constructio techniques. Th followin foundation type ca be classified base on wher th load is carrie by th ground lo at on ip ti or at on raW'foundation etc. Generall th dept over widt (ratio of foundation dept to foundation width) is less than 1.0. ep fo ti pi es er ad nd io ee trench fill Generall th dept over widt exceed 4.0. If we consider shallo foundation in natura clay or granula strata th followin conditions apply.
tr
ti
ne
en
footin widt (Fig 2.1) here ground conditions re ul in bearin capacities en en ip in be avoide becaus of th excessiv widths required To keep settlement within tolerabl agnitude th eu un ti is co ed
be ld us ts
reinforced concrete slab within downstan edge beam an 3m l. om rs ig
Wher soft spot ar encountere in footin excavation an firm ground exists at lo er leve th of stratu houl be ClO.Ostrength. er th fo be to ee th it ma be practica to reinforc th foundation to pa acro
ground at th foundation depth. In clay soil with plasticity inde greate than 20 th minimu recommende founda have plasticity inde less than 20%, foundation ar traditi al ac at im ep el fi ground level. 45kN/m ru ar achieved usin traditiona brick-and-bloc construction here th allowabl bearin pressure of th stratu exceed 75 kN/m an th stratu remain compe-
checke fo th additional loadin conditio an ma need to be widene ou locally.
tr ta
ti ay
ex va io om ac
suitable reinforcement.
ev al th
ar at in il la er of ig
Foundation
design
.,f'\' / ' 1 '
Widene reinforce strip footing. 1.0 mwide C.25P Concrete
Well-compacted ston fill
II)
II .~ l'tl
-5
c.
~. Mai wires transverse
High-yield fabric mesh
40 mm cove
.I(
225mm minimum thickness
Widt varies an is dependen on th ground strengt
Fig. 2.
Widene reinforced stri footing.
20 mm chipboar
Polythen
vapour barrie (500 g)
Tfabri
Fig. 2.
Pseudo-raf foundation
er en un er it is tial ha he ho is placed wholly on th rock stratu If th rock stratu cannot ca ated at as bl pt le an en differen foundation solution should be considered igur
24
crushe ston fill Alternatively, pile an ring beam or pier sidering when thes conditions ar encountered. he us of concrete manhol ring to form mass concrete pier is prac tica ec no ic an af nstr ct on th an
Introduction
Substantiatthicknes f il l p la ce d i n 2 0
of consolidate l ay er s
granular
~::::=.._!..----;----_ __-_-1 - '_ - = -- -_ - -- _ . _ ~ -
--------;-----\ Roc stratum
.-'.c--------------'-----;r
ss
Maximu dept of clay stratu er no or than twic th thicknes of granula fil cushio to limit differential settlement
Fig. 2.
Sloping rock formation.
Note: Al foundation to b e p la ce d o n i mi la r t ra tu m
Quarry backfill
stem foundation.
(Fig. 2.4).
la
tr
fort conracnd, where
Avoi deep footings wher firm clay stratu overlies soft stratu which reduce in strength with depth. Wher footings
be
ee
in ou dation on
is thic cushio
es
le granular fill (Fig. 2 . 5 ) . If
th if excessiv settlements ar to be avoided. In such ground condition th idth of th fo ti should be possible so keepin th pressure bulb within th firm stratum.
Foundation
design
Existing or proposed trees
Thicknes of ston fill e qu a t o 5 0 required in NHBC Chapte 4.2
eigh an distance of tree determined th
--=-+
=====_-===::____-===_===::::
hapter 4.2)
Fig. 2.S Pseudo-raft
ston fill over soft clay stratum. Minimu
15 mm
Deepen footin usin mass trench fillC10P
Ifth re an d ou b a b u t t h excavatio line take foundation down to drai invert level Widt
of trench varies
~ _
Fig. 2. 2.1.
Invert of sewe
Existing or proposed sewers De th offo ting
development (Fig. 2.6); Th dept of footings is governed by dept at whic
number of factors:
suitable bearin stratu
exists
an om ex ti ee or scheme (Fig. 2.7) pt of er ta le 5. fros susceptibility of th stratu
op
tr e- an in
Introduction
Voided ground fI()()( required if dumpling is desiccated
Depth derive fro NHBC Chapte 4. Tables
--.....::--_....
Polythene ·debOndero Claymasteron external face foundation
Fig. 2.
Existing or proposed trees: H, mature height of tree
Wher clay in dumpling ar desiccated compressible material such as Claymaste should be placed on th inside face of the foundations
distance from dwelling to tree
6. shrinkabilit characteristic of an da soil whic exis an whic coul exhibi larg volurnetricchanges becaus of seasona variations. If ad.equatefonnati()ncannot lo de th ,1 th
be obtaine atrelativ~lyshllltr al ed bo
stratum exists
an
th le
Foundations steppe up away tro tree
below ground le el
following alternative foundations can be considered
Widene
reinforced stri footings
consolidated ston filLThis fill must be of constant dept unde al load-bearing alls to avoi an differential settlement (Fig. 2.8) fill beam raft be th th ck cu gr la ll ep acemen used for w e a k strata such as peat an fills.
YM >,
S tT U C tu ra lu s
o f c on cr e
Areaoftensionreinf()rcetrien
~~Ilge.inthe compressipn zone (mill Breadth ofsection EffeCtiveciept of th tensio reinforcemen (mm) •ch .t reinforcement (N/m ar cter ti ng [inks takenas.tfiore than 46 N/mm Characteristic Strength of concrete (N/m Characteristic dead load (unit) (kN/ Characteristic dead load (total (kN) Lever arm factor Length ofshorter side (m) Length of longer side (m
""g
«ee-planting
(trim
Mult
considered (kNm)
Maximum·design ulti at omen on stri of un dt Ms n... ax ig ti t~ en tr dt an an L,. as, Bendin mo en coefficien from Tabl 3.14 inBS 8110; Part 1 : 1 98 5 Bendin mo en coefficien from Tabl 3.14 in B S 8 11 0 Part 1 : 1 98 5 al esig ti te ad ea 0.4 1. tlk) (kN/m I< Characteristic impose load (unit) (kN/ Characteristic impose load (total (kN) Design shea forc du to ulti at load (k Design concrete hear tress. at cross-sectio (N/mm (N/mm Leve ar (= leve ar factor d) (mm) Partia safety factor fo load Partia safety factor fo strength of material
27
Foundation
design Foundation width
Well-consolidated granular fil place in200 mm thic layers an give 4- passes pe laye with vibratory rolle
Excavation
Fig. 2.
minimum
Double reinforced footin on consolidated granular fill
ID
A·
,wea
--oH=:foo_1-50-75 mm Clayrnaster low-density _polystyrene (11kg/~
ro strata _-
Desiccated
P,
....,r-7T--77.T:m:::!.V
(a)
Fig. 2.
ea e mx i contai sulphate or ground is acidic
'6
Fir natural stratu fo at t 1 ef (b
Trench-fil foundations: (a filled ground (b catering fo existing tree an vegetation
Widene
to/fi
reinforced stri footings
.~
'W <& ••
'~
A·
'.
I: vReinforce rin bea
conc ete MassC20P concrete in manhole
'"
A,
Dowe ba linkin bea
I..-
.-I'"[;-Concrete stub column at 4centre
4,
1I
::J .6
'T--r
..
C')
'2
'E
..'-~
'I
beams spanning betwee piers formed from concrete-filled manhol ring or formwor (Fig 2.10). at
tirnate transverse
Usin th Design Char No.1 (Fig 2.11):
ground level.
3.65 10
bd h er e o r
Designed in accordance with BS 8110
feu
40 kN/m 40 kN/m h er e o r
o o n g w id t
Ne uplift pressure Load factor
1.50
40/40
1,0 m. 24)
34.6 kN/m2
3.65 kN m.
moment
10
170
le er ar
25 N/mm
25 la
0.95d
170 mm
3.65x10 0,87x460xO.95xI70 Minimu
percentag
x225 100
292 mm
percentage ishe foundation is show in Fig. 2.13
Foundation
design
1.0
0.95
ttl Q)
II
1J
0.90
..lie:
ttl
0.85
r\ .
0.80
.~
f\ 0.05
0.10
When Mlbcf2fcu fy
M/O.87fyktd.fy ig 2.11
fy esig Char
o.1: leve an
urve or li it tate de ign.
Iv
0.15
l/0.156
CD
.q-
t;~WW/N) .q-
C\ C\
C\
'\ \\
. .
1\\'
--
'\
Lt)
----- -_
' ..'
-_.---_
-_._--
_--_
...
....•
_-"_
-----_.-. -_
-
..
f -
_-
- 1----
.,;
Lt) T"""
,r:J
....
-r-r
'\
t::
'u....
:>.
"@ t::
';;;
\\
;:
'g
.<:: T""" T"""
bI)
.,
-;;;
....'I fi:
c -
--"
Lt)
-------
-
1-------
-,
CD
io
oundation design 2.3
is
able 2.1. De ig Char
3. Rein orce ent: area of groups of bars Area (mm- fo number of bars
Diameter (mm)
10 28 50
12 16 20
57
85
170
142
198 503
339 201
452 804
604
553
1020
1360
2200
3770 50
113
12
1960
(mm)
3930
3220 5030 7850
8040
8850
9650
8800 19600
100 566 503 523 745
449
905 2510
2090
1800
1570
4600
4020
1050 1130 2010
16 20 25
6280
40 50
25100 39200
4910 8040
Diameter ""'cmm) Mass (kg/m)
1260 1960
1050 1640
6550
10
12
16
20
1.579
2.466
50 3.854
15.413
40kN/m 66 kN/m kN/m he
th
Checking at undersid offootin qm
60/0.60
10 kN/m
kN/m Fig. 2.13 Widene reinforce footing.
layers.
Trench fil foundations
s=ne fillin stone II .h ·bsed. This
Tabl
2.2.
ndation.
BS reference
esig Char
o.
Mesh size l p
the
e s
Cross-sectional a p mass pe square metre
(mrn)
Square mesh fabric 200 A393 52
12
200
10
10.9 8.14
Structural mesh fabric 200
100
10
4.53 28
300
100
200 10
785
70.8
6.72 5.55
100
C503
94 168 262 377 670 1050 1640 2680 4190 6550
385 400 Wrappin fabric
Checking 1.35
belo
ground leve
Vertica pressure factor
0.38 (pressur bulb Fig. 2.14
5.70sll
all=3.Q
whe~s
50
Il 15.413
undrained shear strength,
Allowable beanng pressure 0.38
10
38.6 kNtm <45.60
ar
kN/m run 'm necessar to
clay to c-
requirements HB Chapte 4. wher houses ar buil ex ti tu la ap anti these situations must be used with cautio especially if th it an ad al in ic recommendation should be adopte heav should th clays rehydrate.
plasticit inde correction factor
Actual pressure at 1.35m dept
kN/m2
252
142 98.0
A98
Long mesh fabric C785
result
6.16
200
340 604 942 1360 2410 3770 5890 9650 15100 23600
t-
393
concrete fo ting einforce with fabric es B283 to an bottom an pecify concrete ix of C25P
Thes ar only suitable if good bearin stratu is nown to be presen at an economic an practica depth. he stratu lo th as th ll in te at leas 1. time th foundation width. hi foundation is sefu fo site here deep fill thic soft strata or peat beds overli firm natura strata Du regard must be take of th possibilit of solubl sulphate in th fill materials,or in acidic material uc as eats In thes ituations th concrete should have inimum cement conten base on BR Diges 36 (199 edition)
to preven foundation
1. Provid full suspende voided ground-floor construc tion usin full-spa timber joists orjoist on sleepe wall io at sleepe wall ca be uneconomic Alternativel precas beam an bloc floo ca be used en ty ty at al ta thicknes on th internal face of th trench fillto al foun dation wall affected by desiccatio of clays. Th densit th poly tyrene houl be greate than 11 kg/m'' produc such as Claymaster or Claylite woul be suitable 3. rovide the foundation dept then
suitable thicknes of low-densit
exceed g/ ", nsur that th idth of th trench fillis aintaine with ou an projections occurrin at higher levels. If th clays ct te 33
Foundatio design if ee arat uppe ider sections of co cret from th lo er sections (Fig. 2.15).
area whic ma have potentia fo instability, an in active mining localities Th raft foundation ha that inherent stiffload-spreadin capacity is more resistan to differentia settlements. an id used placed on
cantileverin
0.10 48
Fig. 2.14 Vertical pressure unde
1.
at laye
ea an granular fill hich should extend .I6
at th comers
advisabl to remove th poor fill an proof-roll th formatio prio to either replacin th fill if it is suitable fo reco paction or usin imported gran la aterials of suitable grad ing. This method is obviousl only economic when depths of replacemen fill ar less than .5 is ti th it te ld la ar ered inim thic ll th ld ll ll ld to preven hard spot from developing he pseudo edge beam raft is al uitabl fo site here trees an heav vegetation have been remove belo potential
rectangula footing.
Upward heav on sides and projectiqns ca separate concrete atX-X
Polythene slip membrane
Claymaster or similar low-density polystyrene
t.. excavated trench
If
Eoomin
'lI\" (a
Fig. 2.15 Trench-fill foundations (a correct; (b incorrect
(b
Raft foundations s=oarate th
us pl ts
th
pe
sections
la
ve
te
trees
50%
ized crow
hole subsidence
excess compacte
ld mining
or
ve
us
properly This gene ally pe vi
by ua
to on ir
equire
th builde to have
in
th
qu
ca
Se i-rigi raft design
ut
h e o mp a o n
a h e r e n t stiff-
clayey sand whic have issho in Fig. 2.18
c-tain signi-
high
ater table. Th ground loor plan
DESIGN INFORMATION
hould extend
BS Reinforced concrete design in accordance with BS 8110 fo 25°pitch po ad or /m at 28 da Reinforcement: high-yield bars an high-yield fabric
(Fig 2.16). de
Exampl 2.
th pl
ng he
ne
hi
ig
~3.0 erials he formation recompacde hs on it .i
ur be
'J
Face of edge beam give tw coat of bituminous paint
thick-
1.0
to
Tw course clea cavity Finished floo leve
ites wher potential
Construction joint if desirabl
Fig. 2.16 Stepped-edge beam raft
TImber jois or precas concrete floo Fill leve or concrete oversite level above outsid ground level
6 00 m n. to clay formations
l~p......::.t..-'
_)":";"";"';'::"~II:,-'-r-L---,Y
15 mm minimu ston be
r--...o.<~___;,"::""'--,,",--,,_,,:,,'---~_....:.
unless for protectio fro sulphate in th ground
Fig. 2.17 Voided raft
35
Foundation design Th site investigatio
reveal that th uppe stratu
considered pruden to adop
of shallo
fill
pseudo or semi-rigid raft foundation
LOADINGS
Tota unfactored floo load Tota factored floo load
2.40 kN/m 3.66 kN/m
External walls
Roof Factored loads (kN/m2)
Servic loads (kN/m2) 0.55 0.05 0.23 0.15 0.02
Tiles Batten an felt Trusses Ceilin board Insulation
1.00
1.40
lAO
Tota unfactored roof load Tota factored roof load
2. 3.
kN/m
Impose loads
100 mm blockwork Plaster Factored loads (kN/m2)
(kN/m2) 0.10
lAO
2045
lAO
4.20
1.25 0.50 1.75
Part wall
0.15 0.50
1.50 kN/m
2045
Staircase wal
kN/m
0.90
lAO
1.60
First floor
Boarding (22mm Joists 22 50 Ceilin board Partition (stud)
5.25
1.25 0.50 1.75
1.60
lAO
Spine walls (kitchen/Ioonge 100 mm blockwork Plaster
0.75 0.25 1.0
(kN/m 2.25 1.25 0.25 3.75
Imposed load Snow 25 pitc Storage
Brick Bloc (100 mm Plaster
s b lAO
1.26
1.60
coat plaste
3.0
2.40
8.28 (12.10)kNlrn
First floor joists
Lounge 100mm
Fig. 2.18 Exampl 2.1: ground-floor plan Figure in brackets ar factored loads.
0.50
Raf foundation
Staircas
WALL LOADINGS
Firs fl or .9
Ignor windows and doors.
Pl st
Fron wall
5.25
wall
Unfactored loads
Factored loads
(kN/m)
(kN/m)
.5
1.00
3.08
1.40
1.68
6.40
8.96
Gabl wall (kN/m) 34.12
3.75 x6.5
10.5
5.25
10.5
5.25
Tota load (unfactored) (kN)
Walls 19.50
2.45
1.40
30.00
27.30 43.05
Fron wall Rear wall bl wa Spin wall St wa l: Part wall Part wall
30.0 12.75 34.0 12.75 4.37 10 8.28 .4 6.50 31.5 6.5 19.5 3.50
Rear wall (kN/m)
Roof
00
10.5
5.25
1.40
1.0
7.35 8.40
68
Se f- ight ft Edge thickenings
1761
.2
4.8kN/m 1.6kN/m
6.40kN/m Area of raft Weight of raft
10.9 3x6
3m 5k
1761+915 143
Firstfloor
4.20
383 435 487 100 83
Total (kN/m)
-2
1.53
1.40
2.14
2.55
1.60
4.08
Plus impose load
1.50 20.2
Maxi um line load
kN/m
34.0 kN/m
Consider edge beam an raft slab as composit with slab acting ie vera idth ista as 00
Walls 1.40 34.08
Part
3.00 1.20
.4
1.40
(kN/m)
Roof
1.0
2.45
.~
27.30 49.27
40.9 kN/m ressur
wall (kN/m)
19.50
1.40 1.40 1.60
31.50
(kN/m) 27.30 6.30 12.00 45.60
Spin wall 1.40
(kN/m) 2.14
1.60
4.08
1.40 1.40
4.20 1.68
(kN/m)
Firs loor 0.
1.53
1.50x 3: 0m r 0 0 x 2 8.28
12.10
nd
dg st ip
0.93 0.9
46 kN/m2 unfactore
N/ foundation leve generall
coincide with th centroid of th edge
nts. pr ct ce he ro nd pr ssur unde he dg stri is more likely to approach triangular distribution with higher edge pressure Th slab therefor need to have sufficient reinforcemen in th to sectio to cate fo this rotating force. Its main function is stru tura ti hile atthe same time enhancin th edge beam stiffrless. Where tHied ground occurs it is pruden toprovide ye bottom re nforce bl raft sl to sp over an soft spots. woul result in an equivalent eccentricity 15 haveto therefore cate fo an ultimate moment of 0.15 9. N/
he sl will 40.93 1.5
37
Foundation design
Face of raft painte
with bituminous solution
Constructio if desirabl
[oin
Tw course clea cavity.
dt of to to suit ground bearin capacity
1200
polythen
dp
To fabric mesh supporte on stee chairs
150 mm minimum
Fabric mesh with extr bars an link
ig 2.19
hardcore well compacted
xa pl 2.1: af edge beam detail
Fig. 2.20 Exampl 2.1: pressure unde edge beam
Fe
Fy
Edge beam
46
10
9.20
xi um in
10 =0.11 x35
Therefore fa factor
49.2
58.1 leN/
58 1~ From Design Char No.1
87x
9.20
10 0.
Minimum percentage
=156mm bd feu
m' 100
to an bottom la er of 25 fabric
GR UN
BE MS
Self weight of beam sectio pe metr run: 23.6 [(0.45 0.45 0.45 0.15 6.37 kN/m
38
oa
0.95
Therefore
RIME
ode)
Us w[2/l0 to take accoun of some fixity
Therefore
rovide
saggin
es in th ra slab
fa
facto
Th
52.36xl0 450 400
=0.021 35
0.95.
er or
53.36x10 60 40 n'
1000 l6 ba
=402mm 52 mm
Provid A252 Fabric plus tw Tl
bars in bottom of edge beam
Raft foundations Bending
Corner cantilever 1.50
Ultimat design moment
bd I. facto
feu
2.0 65.45 10 450 400 x35
=6.98
0.025
0.95. 65.4
Therelore A.
Reinforcement
10
A252 Fabric 50 mm wide
Vsin design formulae method (B 8110 Cl 3.4.4.4) By inspection is greater tha 0.95. therefore 0.95 d.
12 mm
1000
Therefore
=402
in op
528mm id 25 beams at comers.
....
us
ar in to
3.65x10
A.=--=
0.87/
n d b ot t
of
ge
0.87x46OxO.95xl06.5
=90mm
Minimum percentage Fabric in bottom of toe.
stone fill.
Internal ground beam (party wall
Toe desig Design as
cantilevered slab to carr shea loadin from oute leaf
to reinforced with A252 fabric mesh in bottom Consider 1.
Loadin es
11 mm brickwork= 2.30 x0 x0
6. =·15.6 kN/m =1 0k
Therefore gx
17.2 kN/m
Therefore desig shea
1.40
17.2
24 13 kN/m
b;
a of f
6m
1000
Tw T1 bars
402mm Total
100
106.5
12
0.23 N/mm 00
Referenc BS 8110 clause 3.5. (shear resistance of soli slabs) an claus 3.4.5.2 (shea stress in beams)
fixe element:
Vse thickening. Consider A252 in bottom plus tw T16. Therefore:
Shear stress 24.136x10
partiall
57.50x3.0 10
desi
VI
1 06 .5 0 metr ru =2
45.60 11.90
0.
Ground beam considered to ac as
10
0-
0.
57.50kN/m
length
Therefore b;
Factored wall line load l f i gh t
0.95
578mm
398. mm Therefore: As
-0.87/
Therefore: Design moment of resistance
As 0.87/
6= OK> 51.75
Permissible concrete shear stress ,
Co id mode.
Referenc BS 8110 Tabl 3.9:
100/A. bv
100
is le than required.
e•
b ot h
of
Ultimate design moment
106.5 therefor from BS 8110 Tabl 3.17 no shea stee is
52 in
57.5
en
1.50 2.0
Chec toefor bending
Moment of esistanc of tw la er ofmesh
ownwar de ig load (wall) (toe self-weight) 1gebeam.
5kN
nt
Upward design load from OB
31.0 1.40
15 64
21.8 24.13
kN/m
kN/m
ti ev
Nm
6x
L"
ec in
ta
ba
02
8 7 x 46 0
95
6= Tota moment of resistance
109.30 kNm
se on la er of A252 in bottom of ra thickening it tw laye in slab it tw T1 in to an bottom of beam (Fig 2.21).
39
Foundation Tabl
2.3.
design um ar of ground beam loadings Maximum factored wall line load (kN/m)
External front wall
90 mm
id edge beam
42.27
Part wall
80 mm wide slab thickening 25 nd 25 th op bottom
45.60
75
34.12
Staircase wall
1.0
150mm deep beam nd bloc 50 mm concrete screed Plasterboard Stu partitions
1.0
2.00kN/m2
(kN/m2) 2.25 1.20 0.15 0.50
loor
Dead load Imposed loa 1.50
12.10
As spin wall
8.96
5.60kN/m2
External wall (kN/m2) 2.0 2.0 0.25
100m blockwork 102mm brickwork 12.50 mm plaste
60 mm wide slab thickening ba tw la of slab
4.10 1.50
Therefor tota floo load take as 4.10
to an bottom it 25 fabric es in to beam 10 link at 25 mm centre Spin wall
0.75 0.25
Snow Ceiling
Floors
id edge beam 16 ba to an bottom with 25 fabric mesh in to beams. T10 link at 25 mm cent es
id edge beam
Impose load
Therefor tota roof load take as 1.00
External rea wall
Gable wall
0.23 0.02 0.15 1.00
43.05
to an bottom it 25 fabric mesh in to beam T10 link at 25 mrn centres 90
Self-weigh of trusse at 60 mm centre Insulation Plasterboard Dead load
4.25
Internal wall (kN/m2) 2.0 0.50
l00m blockwor Tw coat of plaste
2.50
Morey flats
Staircases
DESIGN INFORMATION
(kN/m2) 4.20 0.30
175 rn in-sit concrete Finishes
Design codes Loading Schedules of weights of building materials Structural us of masonr Structural us of concret
Foundation concrete: co 35 N/mm2 fy Reinforcement: 46 N/mm 1.50 fo dead plus impose loads. Tf
4.50 Impose load Total
oading
he it in io th up firm cl ys ar In un la bo gr nd .of io he te is ow de arisin from solution eatu es in gypsum strata at depth. In view of this ti edge beam ra il be us d.
3.00
to
7.50kN/m2
alls
External wall Wall Thre floors
(kN/m) 38.25
4. 60 2.0 Total
LOADINGS
71.85
External wall
Roof Concrete tiles Battens an felt
Wall (kN/m2) 0.55 0.05
Roof
4.25
7.80
2.0 Total
33.15 8.13 41.28
Raft foundation 0.23 0.02 0.15 1.00
275 mm----+-i cavity vapour barrie on 38 mm polystyren
0.75 0.25
A252 mesh
1.0 2.00kN/m2
2.25 1.20 0.15 0.50 4.10 252 mesh
1.50
blinde crushe ston fill 900mm
,5.60kN/m (a l/m2)
2.0 2.0 0.25
275mm blockwork party wall
4.25
A252 mesh
>11m2)
2.0 0.50 2.50
A252mesh
4.20 0.30 4.50
mesh
3.00
300mm
800mm
7.50kN/m2
__
(b)
Fig.2.21 Exampl 2.1: reinforcemen detail to raft foundation (a External edge beam (b part wall thickening N/m) 38.25 33.60
Spin wall
Three landings
Wall
2.50 8.0 5.60 7.0 2.0
Three floors
71.85
Total Staircas
33.15 8.13 41.28
20.0
Wall Three floors
4.25
9.0 (average height 5.60 2.0
Total
58.80
38.25 25.20
22.50 85.25
WO
78.80
wall
2.0
rush ng stre gt bloc it rtar signat on (i i) /k =·8.2. Design vertical resistance of wall unit length {3tA t'm
41
Foundation
design
where f3 i s pa ty ed ti or ba on de ne io bl 62 97 »; is he ic ng he on ta la 23 be 8 .2 0 / m factor or blockwor obtained ro Clause 1: is th pa tial afet 27 ak 3 .1 0 wall thicknes in millimetres. Eccentricity at t. to of
ec
co
to
dl
le
3.0
Usin 3.50
0
(
strength blockwork.j
II
3.10
hef
59.00kN/m
100
tef
e si g
Therefore
f3
3.50. Therefore
0.53
26
1 .5 0 = 9 .3 0 kN/m
Therefor us 3.50 roof level
Therefore ic
oa
oa
nc
10 3.10
/m
ec
140kN/ oa
crushing strength blocks from second floo to
8kN
af
ex
ec
Usin 7.
Th ere,or vertical lo
52.5
~100:..:....:..x:_:6:.:...:.4.:. 109N/mm 3.10
th
oc
kN
Therefor us 7. crushing st engt blocks fo al th inne leaf to th external wall from ground floo up to th second floo level.
RAFT DESIGN
1.50= 78.825 kN/m OK in
56.10
3.10
6 .1 0
6.40
esistanc
he second floor.
6.40. Therefor
I09kN/m
109kN/ esig load
e =
3.0
strength blockwork.jj
(kN/m) 33.60 22.50
strength blockwork.ji,
II
78
ls
Wall Floo load Blockwor 2.50 9. Usin 7.
pp ie
al
or il
om
/I
ta
ac
nt of om
41.28 kN/m
ailS
41.28 kN/m
First floor
I,
_j
~~----(l E '
f,--=--(I
~I
~I
~I
250m mil
Span
L_~
ILWaIlS 4.00m
-t--~ VJ
-'"
-'"
Cj
Cj
'0
2
ro
4128kN/:$
00mm
250mm
I t )
-'"
to
t:
a:
-,
Fig. 2.22 Exampl 2.2: ground-floor plan of three-storey flats.
42
---stairs
41.2 kN/m
.11.
250 mrn
3.00m
IJ100mm
"II~
4 .0 0
250mm
Raf foundations
",~/m
nm
3.5
blockwork
kN/m Precas floor s e c o n d floo to
7.
blockwor Provid 35 mm mm galvanized steel restraint straps at 2.
_3.60 22.50
10
blockwor
6.10
250mm
8.00 il
F.g. 2.23 Exampl 2.2: typica cross-sectio storey flats.
~mnerlea to lor level.
fixity Maximu 85.25
line load
5 .2 5
lo
Slab desig
ac
d on r x 1 x 1
127.875 kN m. Therefore
Ultimat moment (sagging)
127.8;g
42
204.60 kNm
682 0x
In featur
127.875x2
nmat moment (hoggmg)
an
5
2507
From Fig. 2.11: 255.75 10 600 550 x35
Therefor lever ar 519mm.
A.==0.87/z
facto
0.04
0.945 an therefor
x2
m 550 mm
bd
0 .9 4
55
Loa spread 8,73 8.31 72.6 Therefor average bearing pressu belo slab 2507/72.60 34.50kN/m Assume slab span simply supported. Maximu span 4.0 m, 34.5
255.75 10 0.87x460x519
1231mm
Therefore net uplif pressur 45.03 kN/m Tr two-wa spanning slab simply supporte at edges. Provid spin beam across centre of raft Ix= 4.0m, ly =4.0 I}
1 1 l s . , = a..xn
a.yn
msy=
Shear
Ii
From Tabl 3.14 255. kN
==.I..
i,
=0.062x45.03x4 =44;66kNm
Therefore minimum links require s=250mm 40 60 50 0.87x 46
Therefor minimu 157mm Maximu
as.r "=0.062
as, =0.062
0.45 N/mm2
MObs 0.87fy
4. =1.0 4.0
Iy=
5N
bd
~Omm
1.50 0x
Ultimate desig loa Less eigh of slab
(kN/m2) 51.75 6.72 45.03
Therefor us four T2 high-yield bars to an bottom (125 mm-)
Vc
ofthree-
tw le
spacin of link
TI 0.75
msy=
Iy =4.0 3.0
t,
150 Il1Ill2
62
03x
44.66 le
1.33
0.093 sy
link at 250mmcentres 0.
55
2m
m~, msy
93x 5. x3
=0.055 xA5.03x
=0.055
=3 69 kN 22.28 kN
43
Foundatio
design
1L
4T20
250mm
150 mm in well consolidated granular fill
ig 2.24 Exampl 2.2: ra edge detail
Forfell
35 Njmm? andfy 44.6 1000
bd fe
10
10
77
93 up th 0m 10
bd fe
Therefor Th
er or
93 ba 37.6 10 5 5 x 1 5 0.935
mm? 1m th to
nt
op
b. 37.6 kN m. Therefore:
0.044
ection placed on concrete ad foundation an ille it as concrete he to sectio of th pier ca be reinforced to form connection fo th reinforced concrete ring beam placed at clos to grou level. This etho co structio ca also be used here existin drainage is to clos to proposed al foundation In al case th pa foundation must be wholly on simila bearin strata.
0.87x460x155xO.935 th 39 in bottom of lab.
2. .1
m' nt
to
PADANDPIERFOUNDATION
This type foundation (Fig 2.25 ca be used in situations er li ei ly el ings ar affected th cost of piling ca be prohibitiv becaus of th initia co gettin th ilin ig to th site is used it cl ea ll te
44
delays can be reduced.
0.935
br 93 up in both directions it
2.6
constructio
155x 155x3
0.87x155xO.93x460 br
encountere becaus of past quarryin or geologica faulting,
460 N/mm
Di
it te el ar in sites, usuall duri excavation fo th foundations. he ls ar is to it lt ic ie l. il th cret lu it co ld er iv th im co ta deeper than is to fill th well with 15 in le-siz tone tw ce ia l. cl io th er ll te be required to pa ve th ell. Th beam should exte sufficient distance beyond th well this minimu distance is generall take as th well diameter each side
Pa
an pi
oundat on
50mmC10P oversite concrete on 1200'gauge polythen dpm Timber suspended ground floo
Note Al foundation to be on simila strata
Fig. 2.25 Padand pier foundations,
followin remova of larg sandston as foun to be ep te
cove (Fig 2.26). The well' h i 1 .0 m th un
ve he lpp xi l y 2 .0 m di te he 2. wa brick-line Th well wa positioned belo th junction of th rear alland part all. It as notpossibl to epositio th of-a te configuratio wa adopted.
al faulting
filled with be reinforce t- ring beam
wher
exist-
idation. In al li
ea in
4legTS
~L 40 mm min._...jI---
ce tr
cover
on housin
ations, When af without
roundwater gle-size ston nc
ou ,di
te nc
Fig. 2.26 Exampl 2.3:. disuse well foundations. Concrete mi 30 N/mm at 28 days reinforcemen to be high-tensile bars allowabl groun bearing pressure 80kN/ minimum.
45
Foundation design
Helical reinforcement
ta
ta
Fig. 2.27 Bore pile constructio sequence. Stag 1: Coring tube with cuttin edge to suit ground conditions Stage 2: Shaf full formed temporar casing ma be required in water-bearin gravel an sands. Stage 3: Helica reinforcemen placed an spaced of side of shaft. High-slump concrete poured Temporar casing ma be required while maintaining head of concrete in shaft. Stage op do il
Factored dead load Factored liv load Self weight of beam
kN/m
Therefore us four le T8 link 30 cent es to satisf laus 3.4.5.5, whic stipulates that no longitudinal tensio ba should be urther than 15 mm om ve tica le of hear link
50.40 19.20 11.20
1.4
kN/m
Be
span 3.50
on to
BEAM
pa foundation 3.50
Ul timate lt
he
14
540mm. Usin Fig. 2.11 b=600mm
30 Nrmm?
feu
Reaction from beam
141.40kN
Factored dead loa Factored live load Self-weight of beam
23.60kN/m
123.75x10 =0.024 60 x540 x30
bd feu
kN/m
33.0 5.12 11.20
Tota load
49.32kN/m
3.20.kN/m
1.60
z=0.95d
Therefore: 0.87x460xO.95x540
0.87
herefo provid T1 in top.
ou T2 mm ba
=602 r n in bottom of be
with th ee
sv
46
0x 0x 0.87x460
mm /m
550xl0 feu
Therefore Therefore:
V= 141.40xI0 =0.438 N/mm2 60 54 100A, l00x4x31 0.39% bd 60 54 Ve 0.4, provid minimu
0+
Vult
Shear
0.46 Therefore:
-550kN
ult
540 x30
kN 0.105
0.86
0.87x460x540xO.86 links throughou beam
Therefor provide four T32 mm ba T1·2in top. V= 244xl0 =0.76 54 60
in bottom of be
it th ee
Piled foundation Therefore 100A
/;;iTherefore
Vc
m in i u m
nk
a xi mu m
Vc
a r r eq ui re d
u l i ma t
o me n
0.225 x15x-
Nm
Hence
re mm'
10 x350
100
PAD FOUNDATIONS
93kN/m kN/m
whil
0.45
In
satisf
here lo of dwelling requir specia foundation an th fill or weak:groun ar no suitable fo ground improvemen ec iq es li ca ca ie ittl ex co provided th design detail ar carefull considered In most situations driven pile ar used driven to predetermine se 0t working load. ed railwa
clause
further.
rt
kept as high as po sible.
ll ad
er
ne
ll ad
rea require
is ofte more economic to de ig
ta en on to ar ay th le in usin smal ini-type pile in yielding strata such as clay an ands is that th en bearin co ponent of th workin
x-
= 1
::>.12
il ca va ov ista ce ille cuttings an backfilled ston quarries fo example.
damage becaus of th eccentri load applied.
=5
11.20
455 mm?
2.
nfa
34.8
re
ri en
ep
to
ck
fi ie
ki
ctio
being ver costly. here pile ar driven or bore throug filled ground stil ettl ng er ts gh llowan ad th itio al lo ri ativ ic io Also on site wher highly co pressibl strata uc as peat
100-9.60 4 00 m
h ic k p a
f ou nd a o n
additional load will be transferre to th pile shaft.
Base reinforcemen d:::
a x u m u lt i a t
o me n
5x
_!:!__= bd fe
.m with thre
10.848xI0 10 350
Therefore l.
Th
e ro r
040
.d
2.0 0003 30
0.95d 1O.848xl0
irnmum percentage
0.13 x 1 -100
82
mm
x 3
Thes ar generall formed usin si pl tripod rig. here er un te le of clay ic au ck g, th em or ca ng ne ee ev ld ed ea ar er ised when withdrawin temporar casing an sufficient head on et ld lw nt ined th le preven neckin or concrete loss Bore pile usuall rely on en bearin an ki friction to er
ou
te
pr
em ex
er
ta
Foundation
design
asin ha to be nsidered th bo ed il ca be neco nomi compared with othe faster systems. ei main ad anta is that they an inst lled quietl with minimu vibration; idea when piling clos to existing buildings.
where N; bearin capacity factor undraine shea N; stre gt of th co esiv strata at th il as al es fo cohesive st at ca vari bl ar epen en he angl of internal friction ¢. Fo estimating purposes valu diameter.
Base resistance granular strata
this ca be checke by overboring severa piles.
Th base resistance in granular stratu
installin bore pile Differen cuttin tool ar required fo the variou soi conditions.
is give by
q= rDNq
calculated usin th Skempton formulae whic combin both en bearin an frictional properties of th pile Fo varyin soil strength th skin friction is considered fo
where Berezantse grap (Berezantsev 1961 base on th angl of shearing resistance is usuall determined from th standard penetratio test result value
friction bein considered when passin throug filled ground
boring operatio
s-
surroundin he al safety of fo skin friction Qu th ultimate resistance of th b. Qs is th ultimate valu fo skin friction shaft pile Qs area 0.45c 1t dh 0.45c. Qb is th ltimat al en 1t bearing wher isth cohesi al of th clay et rmined la rato testin by th us of fiel tests: i.e penetrometer or shea vane tests. Thus Allowabl workin load fo -(ltdh
pile
~s
loosen th strata an
th pile an should no exceed
MN/m2.
Shaf resistance in clay soil
he shaf resistance
is iven by f=aC,
where strength. strata wit C«
undraine
th
If)
vertical elements usin th appropriat values down th pile length.
Estimation of approximat workin load is as follows. Th ultimate load capacity Qu=Qb+
where Qs ultimate shaft resistance, ultimate base area resistance, ultimate unit en bearin resistance Ab
q=N; Cb
of
lie betwee
tan
where dept to base of pile or base of th granular strata whicheve is th lesser dept to th to of th gran la strata; (j angl fricti etween th ranula st at an th il sh ft K; eart pressure coefficien dependen on th relative densit of th soil and (j fe ti ngle sh arin esistanc anul soil for variou type of pile an relative densities. Fo driven piles: Pile type Lo relative density
High relative density
0.5 1.0
1.0 2.0
effective Steel Concrete is enerally take to
cohesive strata is give by
al
.2 .0 into th clay strata an th prevailing ground conditions Th shaf resistance/i granular soil is give by
ndc(2.7h+9d) 12
Base resistance: clay strata
shea
50 kN/m2 N/
nd xge) 0.45e) +--'-----'-
ultimate unit shaf resistance on side of pile As surfac area of pile shaf considered as loaded
values of 28-3
th valu of
as obtained from th and K, 1.0 or th lo se in effe he ri (j =220
sh ld out.
us
to cate
Piled reinforcemen Th
expression
(D
d) K, tan
652
Th shea strengt
326 kN/m
Allowabl end bearing pressure lu
9x326 =978 kN/m
Xc
En bearin capacity
97
1tx 0.
27 kN
(kN/m2): Relative densit
by
SKIN FRICTION <0.35
==adhesio factor
0.35--0.65
==
0.40
==34kN Therefor pile capacity
27
cxA,
0.65--0.85 of tp is
110
>0.85
:s results value ~"rled as th 'f 28-30°
Base on soil site investigatio
ha revealed that loos colliery wast fill abou
ca th ll nl be ce on stil consolidatin unde thei ow weight Th strata ar describe in ig 2.28 an 2.29 i st i ul de os dw li it co di on is kn ha id th to id bo le do th ud ne ut be ground level.
enetration tions. result"a
in ti bo ho availabl fo th fi m/stif brow
2.45
34 ==311 kN. udston this valu isconside ed
trat in borehole no
Figs 2.29 2.31 00
x t 0.1(18
7.
0.65
20) (z
0.45
1.3)
26kN
Therefor pile capacity required For
==152, unconfined compressive strengt 13 152
2022 Shea strength =Allowable en bearin
clay an
trxO.4
Require pile capacit Negative skin frictio
weathere mudstones. Th maxi um pile loadin is 30 kN bu an
by
50
r o
it 1. penetratio into th adequate or borehole no 1.
igut
lie between
0.40.
eathered
2022 kN/m lOll kN/m2
capacit
0.45 )/4
xlOll
conservativ (Fig. 2.30). ilar strata, th
granular
Po
strata an
¢e
on
"act
ef-
From Bjerrum raet 0.20 po fo clay of lo Th negative skin frictio factor ==0.20
tp for .y
This is greate than th 45 kN required Th pile us therefor ne 1. in th d st o ll lo th weathere zones. Th minimu cement conten in pile should 7 0 / m sulphate-resisting cement with free wate rati no exceedin 0.45 to cate or Clas sulphate in soil
uni negative ski frictio effective overburde pressures the effective angle of shearing resistanc Po tan ¢e
Ski frictio ultimat Require pil capacit
==
plasticity PILE REINFORCEMENT
haAS
30 kN 40 N/mm With 75 mm toleranc on pile position th bendin pile shaf equate to
High relative
Thi is approximately
nsity
1.0
Therefor total pil capacit require EN
om
nd K,
75
0.20(18x3.80)
70 'vJ
~"ac,poAs
1.0
10 ==300
38
33 kN
BEARIN
(soft rock).
458)
732 10 450x450x4 ==
For
(1.6
54.96 450
omen on th
54.9 kN(ult ==
0.090
40
Therefor us 'nominal stee only Provid seve R1 vertical bars it nomina R6 helica binder at 15 mm pitch.
Foundation
design Sheet 'r
L../GHT
CABLE
PER.CuSSION
HUDDERSPIELD
Ao
DescriptionStrata
MADFi!
GlbUND:
w·ci1t
6(JMQ.
Borehole
~S;::;i:;:te:---=--...L.---==----I
DIAfrtETE:R..
122·0
1. 1.
Co/IIU.j
Depth (m
egen
fAP..Sbe
c oa l
Remarks
ig 2.28 Exampl 2.4: bo ehol .7
Driv
1.
il
an ag es weak or water-bearin strata withou an change occurrin in thei cross-section. They ar generall le friction (adhesion) ca be de el pe he rive thro gh be placed throug
In th ou in fiel thes usuall consis of teel tube filled it concrete recast concrete eg enta iles concrete
50
Piled reinforcemen Sheet of
Boring Method
LIGHT
PEra:.USSION AT
CABI.E
Samples/Tests ample Type
StandI
Redu
HUDOERSF/cLD lor> Descriptio
Insitu
fll/AOr=
Site
ISO NM DIAmETER.
12/·00 Scale
GROUND Muds :m
CU'Id
Borehole No·2
Depth (m)
of Strata
Legend
a/ld. froe~s,
Shak
brick.
timr:w-
_g;Q_
'2 ·qo
,6.0
MADE
6ROVNO:
mADE
GRoUND
ISrick.s sfoI1es nd c..~s
tV (4-)
3·!i"C!
hA.ck. a.6h
fr"$~5
brick
..1Q;Q_
(,'0
....!bQ_
mADe
GROc.JND
...illL
CA'J,t
7';ZO
c r ~ ~v~
f!~~ <.
=16.0
SCu1d..st-oNl. a J K l b~c/(
~5~~
18.0
uJ~ed.
IV
;:
e""~
.
~
; -
-:-=--
E;~
(152)
&r~~
('IWcL~
2·50
and.
o.
t't-r.i.n}:t_
:_:.
-=---=-
rtrat:
f{o..3~ Oark:
.
;-:::::-:-
1.U€CAk~
;"'IAj~~
..
S'.<;;>n
btZ-dd.u1.
Mt.JCk;1-o SU$p~
!LeS
ai:
q.
ti1, M.
sero":)
-20.0
Remarks
Tn:u.e-s
Borehole
wa..ter enbered:
cir;J on
bore~
Wtfk:J.rr:iwa)
cW~tnj
drliW'lj
cd
j\.(
GaSCM.J
Fig.2.29 Exampl 2.4: bo ehol 2.
..ithout any generally
ar
.n through
th clay or gravel overlyin th bearin strata. Thes pile ar usuall driven to predetermine se base on th Hile formula whic is dyna ic criterio relate to
is ad
ed
establishe
ep tl
ia at an ac ag
il en io
se criteria ar valid.
51
Foun Founda dati tion on
desi design gn Grou Ground nd leve leve
122.00AOD
0/'\\ 0"
450 dia ---to
'YW= 18 kNlm kNlm
- ---- '
1/ II.......
')'0 ,~
r5
Made Made ground ground colli collier er shale shale bric bricks ks clay clay timb timber er etc. etc. (N values 4)
r~~".:..'
:...D_:_-+=-!;2~,8~0
_M;;d;
k:;. ~\
",Clay ",Clays, s, and coal coal
....::.__:;,_~ --=-
.00"
'...:. ...~
. .D~~,80
b.. o_:"
-Assume 50 kN/m2
_clays
-=
-=~~
to stiff
C':1 -~----.
-==---=~--L5.10
_--....
~,i;;,---''I>. ~-I.
CD
~N
' .
49 blow blow
--==--
~S;~~/~2
0,2.5
~,50
Fig. Fig. 2.30 2.30 Exam Exampl pl 2.4: 2.4: grou ground nd cond condit itio ions ns at bore boreho hole le
«' ia . 450 m m d ia
•.
'J'
1l
s:
0. II
Made Made groun groun ash, ash, clay clay kN/m 'Yw 'Yw== 18 kN/m C\l
'" .,;
or-:.
II
CD
Ol
()
CI
.0
-7.20
'C':1
-8.50
N=
152 blows
Fig. Fig. 2.31 2.31 Exam Exampl pl 2.4: 2.4: grou ground nd cond condit itio ions ns at bore boreho hole le 2.
52
Desi Design gn phil philos osop ophy hy
Note:
Whn s+cl2
where
l:
th pili piling ng ha mer; mer;
c:
dolly;
,;._
tota tota temp tempor orar ar
'0
roun roun
it
or
wa er pr ssur ssures es th re-s re-s rike rike se
rive rive
furt furthe he
wh
oa
xc ds
sted sted
he pera pera ng ch ra te is ic
he ibra ibrato tory ry
rs sett settle leme ment nt reco record rded ed
R =
_'-c/2
where
ltim ltimat at
ad
kN mm se blow blow 00 =---=-----=7.11
s,
unt. unt.
refo refore re
mm/blow
beam beam desig desig
Genera Genera notes notes
he si nv st ga io ha ve le de roun roun su ti fr fill filled ed-i -i clay clay pi clos clos to bric brickw kwor orks ks Th fill fill cons consis is of soft soft clay clay mater material ial wer eviden evident. t.
-7.20
pile pile shou should ld be used used '-8.50
DESI DESIGN GN PHIL PHILOS OSOP OPHY HY N= 152 blows blows
it is reas reason onab able le to desi design gn them them as simp simply ly supp suppor orte te an prov provid id to stee stee ov su port port quiv quiv le he otto otto st el Th il sa sf
53
Founda Foundatio tio
design design
Seco Second ndar ar
load loadin in
beam beam
Note Note Refe Refere renc nc beam beam supp suppor orti ting ng dial dial gaug gauges es to be supp suppor orte te w el el l c le le a o f t es es t a re re a
Main Main load loadin in
beam beam
150mm Deflec Deflectio tio readin readings gs t ak ak e f ro ro m d ia ia l gauges gauges suppor supported ted steel steel refere reference nce beams
75mm Load Load cell cell Hydra Hydrauli uli
Piec Piec of scra scra stee stee fo leve leve read readin ings gs on al anch anchor or piles piles
jac
300mm
\\'/ \\'/ ,\\\ ,\\\ t//~\; t//~\;<,, <,,\\ \\ Anch Anchor or piles piles Test Test pile pile
Elevation
-
Plan Fig. Fig. 2.32 2.32 Stat Static ic load load pile pile-t -tes esti ting ng arra arrang ngem emen en usin usin tens tensio io pile piles. s.
cr ckin ckin over over th uppo upport rt Grou Grou floo floo cons constr tr ctio ctio to be full full susp suspen ende de usin usin full full-s -spa pa timb timber er jois joists ts at 40 mm cent centre res. s. Prov Provid id 40 mm wi by 60 mm de rein reinfo forc rc on rete rete roun roun beam beam .5 mm diam diamet eter er stee stee tube tube driv driven en to pred predet eter ermi mine ne se an test tested ed to 1.50 time time th safe safe work workin in load load
Fo resi resi enti enti elfelf-co co tain tain ho sing sing unit unit impo impo ed load load ar 1.50 1.50 kN/m kN/m fo floo floors rs nd fo flat flat roof roof up to 0°pitc 0°pitc to hi access access is possib possible. le. be 0.75kN/m
rovi rovide de th im os load load is tobe 0.75 0.75 kN/m kN/m up to 30°. 30°. Fo ro lope lope grea greate te th 75 pitc pitc th impo impose se lo iszero iszero
ASSE ASSESS SSME MENT NT OF
AL
OA IN
Code ofpract ofpractic ic fo dead dead an impo impose se load load 39 (198 (1984) 4) Part Part Code Schedu dule le of weig weight ht building building materials. materials. BS 64 (196 (1964) 4) Sche kwo cons constr truc ucti tion on with with timb timber er grou ground nd an firs firs floo floors rs an trus trusse se raft rafter er
calc calcul ulat atin in
th line line load load toeac wall wall
dete determ rmin ined ed by line linear ar inte interp rpol olat atio io betw betwee ee 0.75 0.75 kN/m kN/m sl pe an er fo 75 lope lope Fo re iden identi tial al alco alconi nies es an tair tairca case se impo impose se lo ds ar take take occupancy. stai stairc rcas ases es land landin ings gs etc, etc, th impo impose se load load ar to be 3.0 kN/m2. kN/m2. iv
cces cces bu with with
mini mini um of 3.
N/m2 N/m2
ss ssme ssment nt
20
10
A.......
! , . - . ·_ · . .
..
-2
. .. .. .
. .: _ : : : : ~ ( _ : : : : ~ J ~ · · ~ : _ : : : : ~ : .:.I. _ . . .
l· ....
-.
....
. _ · L ; . • •· .· .· _ · · ·......;... ·
~.
·-i..·.. ! - · ~ · : - · ···. · · : · .- ~- ': .· ·: · · · - -: · · ; ·-·- · · · -·-· · · · + :r:r : _ :
oadi oading ng
40
30
~ i = 1 l i l i a 4 . : _ ~ · · : " . · · _ t · · = _ · · .~· ·. · ,. ·; ·; L~~ = : t ? d _ : . · _ T : · . L. ·
!:":::~ "'_;_ ""i.-...I''''''' ..I'''' '''i''' i''''' ''
of wa
+·I__
+ . · - - · ~ · ·..· ·- -~ · ·· · ~ · · ! - - · r · - · . ·. - ~ : ~ _ ~ · i - - ·· .·- . . . . . . . -!
-!
--+--+-
1 ' 1 · . ; . ... . .
--!-.
.+-~~--~-+~r-+--+~~+--r~~+-~~--+-~~~+-~-7--~~~--~; ... ·. ... ... .. +':..
~:
, . !!:..::
r· r: r:
·I
-8
"j
_~
._
Load Load (ton (tonne nes) s)
Fig 2.3
o ad ad -s -s e t le le me me n
lo
;.-
..
....
····-r·
~.
:::~::.'
..
····1·······; ,.,.
'.:!:"
r':'"
(I)
(J
10
Time (h)
no acce access ss
Fig 2.3
30° ed o a
z er er o
0°
/m
Roof
Impos Imposed ed load load
Dead Dead load load
(kN/m (kN/m2)
Tiles
0.55
Trusses
0.23
Factored
25° e ilil in in g a cc cc es es s
0.75 0.25
oa
0.05 •-
be
S,
corridors,
.0 kN/m2.
,..'0
h ic ic h h e
Plas Plaste terb rboa oard rd Insulation otal
ceil ceilin in
1.0
0.15
i m o se se d
0.02
1.00
lAO
1.40 kN/m2
re
p os os e
oa
oa
1.60
1.60 kN/m2
2.00 kN/m2 3.00 3.00 kN/m kN/m
55
Foun Founda dati tion on desi design gn
ro
lo
an
Wall Wall line line load load
irst irst lo
Dead Dead load load 22 I11boarding 22 ~Omi ~Omi jois joists ts Plas Plaste terb rboa oard rd an skim skim Stu Partit Partition ion
(kN/m2) 0.10 0.15 0.15 0.50
Factored
Cons Consid ider er typi typica ca deta detach ched ed hous hous with with plan plan dime dimens nsio ions ns as show show in Fig. Fig. 2.35 2.35
WallA Unfa Unfact ctor ored ed Fact Factor ored ed 1.26 kN/mz
Roof Roof nomi nomina na 0.
widt widt
.5 2.0
Impose Impose loads loads
Ground Ground floor floor
2.0
2.40 2.40 kN/m kN/m Tota Tota unfa unfact ctor ored ed dead dead load load Tota Tota fact factor ored ed dead dead load load
impose impose loa
2.4 kN/m2 kN/m2
Walls: Walls: averag averag height height
Wall
3 . 6 6 kN/m
impose impose loa
(A)
.7
24.375
34.125
total
34.975
50.265
Wall Wall Bl (sta (stair irca case se sect sectio ion) n)
Exte Extern rnal al wall wall (kN/m2)
Unfa Unfact ctor ored ed Fact Factor ored ed
Factored
5m
ROQf(6.0 0.25
Plaster
5.2 kN/m2 kN/m2
2.0
First First floor floor
2.0
Ground Ground floor floor
Inte Intern rnal al bloc bloc wall wall (kN/m2) 1.25 0.50
Bloc Blockw kwor or 10 mm Tw coat coat plas plaste te
Factored
.0
Wall
Roof
4.2 kN/m2 kN/m2
.4
2. x6.6 x6.6 2.0
Roof Roof span span
C2
F == == - = 250 mm
2.00m
qEt""" Fig. Fig. 2.35 2.35 Exam Exampl pl 2.5: 2.5: floo floo plan plans. s.
56
Floor Floor spa C1
100mm
Grou Ground nd floo floo
4.0m
32.02
46.08
27.22
38.70
ct
-.
81
28.86
Unfactored
sp
.r
3.66
Wall Wall B2
Factored
82
2.40
x5 ll (Bl) (Bl) tota tota
wall wall (kN/m2)
2.0
Walls
2.45 2.45 kN/m kN/m
Part Part
6.50
Floor Floor spa
250mm
First First floor floor
Factored
,""
Pile loadings 2.4x4.0 2.0 2. x4.0 2.0
First floor ,r
show in
Ground floor
Ground floor 4.80
7.32
2.0 .7
Walls
Wall (F tota
Walls
WallG
c.cd Factored
m)
(kN/m) 1.50
10
Wall
50.265
Unfactored Factored Roof nomina 0. Walls
widt
0.
2.
al (D tota ored Factored (kN/m)
First floor
3.66
First floor
46.08
25.375
35.625
WallE
3.66
28.86
2. x2.0 2.0 2. x4.0 2.0
Ground floo
(kN/m)
(kN/m)
4=
1. =21.01
Th calculated wall line load ar summarized in Fig. 2.36 he il yout hown Fi .3 roun ams: 60 00 id Self-weigh 5.76 kN/m Ti beams: 30 ro 30 wide Self-weight 2.1 kN/
4.80
7.32
2.0
Ground floor
2.0
il Unfactored
4.80
7.32
34.975 2.87 2.0 27.2 4.17 2.0 5.76
(4.175 2.0
= 1
38.70
Factored (kN/m) 9.90
.6
PILE LOADINGS
Wall: 100 mm blockwor
('~d
.7
=14.95
Wa/lD
34.125 75
bloc work
38.70
7.32 7.32
.6
50.27 56.82 2.8751
Factored 50.625 2.87 2.0 38.7 4.17 2.0
20.30
72.25 80.78
x 3
Total
il
WallF Unfactored Factored 2. x4.0
First t\jpr
4.80
7.32
(kN) 2.875
34.975
l~
_.
(kN) 50.265
6 22 7. 2
2.87
72.25
_.
( 38 .7 0
:c _.
I.
(J1
c.
8 .9 5 ( 2 . 33 ) _. _.
0>
(J1
.5
( 6. 37 )
I~
I\ (J1
i:.>
0-
(J1
I~
(J1
~.
I\
(J1
Oi !>
C!
,EJ
<0
(J1
\)
6 .8 2 ( 53 .4 0
Fig. 2.36 Exampl 2.5: wall line load (kN/ ). Factored lineloads sho~
C!l
2 7. 2
( 38 .7 0
Co)
in brackets
57
Foundation 34.975
design
3.475 2.0
4.55
0 .7 6 6.37
2.0
5.76
(2.875
3.475
4.175)
30.3
14.15
.0 .0
8.0
2.875 2.0
20.34
0.70 2.875
9.54
Total
66 97
30.20
2.0 2.875
14.04 =239.07
214.95
PileS Pile
Unfactored (kN) 4.55
4.175 -2.0
27.22
2.0
3.475 2.0 5.76
5.76
2.0
Total
=139.58
2.0 3.475 2.0
198.71
27.22
5.76
4.175 2.0
56.82
3.175 2.0
50.83
x(3·175
5.76
le 39 22 Unfactored (kN) 2.0
3.475)
20.34
21.01
24.58
21.01
18.280
2.175 2.875
29.67
Total
114.39
7 .6 7
4.175 2.0
16.70
--
2.875 2.0
30.20
3.475 2.0
36.50
3.175
25.40
2.175 2.875
43.62 165.71
Pile 73.15
2.0
Unfactored
Factored (kN)
21.16 2.0
2.875
8.28
2.0
..,.
36 82
2.0
2.0
2.0 58 45
53.4 x3.1p7 2.0
3.475
127.39 (181.23)
139.58 (198.71)
0.70
-1 07)
Ti
beam
-1 -~ ~ CD
..; (128.56)
(183.16)'
(192.96
175
13.29
x--
(kN)
4.175) 2.0
2.875
Factored (kN)
x(2.875 2.0
2.0
12.020
2.0 2.875
5.76 pi
9.50
4.175
5=
2.0
on
4.175 -2.0
Factored (kN)
Fig. 2.37 brackets.
xample 2.5: pile la out.
ltimat load (k
show in
=84.77
Ground beam anal si 15
I.
.0
3.475 2.0
24
Pile 11
2.0
Factored (kN)
(leN)
otal
=239.07
=171.02
=245.33
(2.175 +4.175) 2.0
25.375
3.0
18.95 Factored
Pile
5.76
(leN)
·.175 ,.1/5 2.0 '5 .475
.175
13.29 16.70 30.20
32.02
3.175 2.0
32.02
.l:2_ 2.0 (3+3.175) 2.0
5.76
50.83
(leN)
28.425 28.3
2.0 (2.175+4.175+3.0) 2.0
26.92
3.17
113.10
3.0 2.0
42.50
8.0
37.36
69.12
2.0 3.0875=
17.78
192.96
73.15
2.0 3.0
Pile 12
24.70
(kN) 25.375 36.82
(kN)
4.175
4.175
3.0
3.0
74.36 80.10
PileS Factored (kN)
Unfactored (leN)
18.95 18.95
Factored
46.08
Total
43.62 165.71
35.625
= 1
36.50 25.40
80.56
5.76 2.16
3.175 2.0 3.0 2.0 6.175 2.0 4.175 2.0
2.0
3.175 2.0 28.42
28.33
4.50
__lQ__
2.0 6.175 2.0 4.175 2.0
44.97 42.50 24.70 6.26 118.43
p7 =84.77 .0
Pile
tjIJ
5.76 2.16
6.175 2.0 6.175 2.0 4.175 2.0
113.68
53,40
17.78
6.175 2.0 6.175 2.0 4.175 2.0
164.87 24.70 6.26
Total
Pile 10 Unfactored (kN) 2.02
3.0
5.375
2.175 2.0
5.76
Factored (kN)
2.0 27.59
2.175) 2.0 Total
35.625
3.0 2.0
69.12
2.175 2.0
38.74
3.58
28.70
Th calculated pile loadings ar summarized in Tabl 2.4. im or il lo ve to nt he additional load du to elasti shears If thes ar to be considered then it is approp iate to multiply th orking load by 1.25 Maxi um
orking load base on pile
171.02
1.25
se 165mm diameter stee tube pile driven to predetermine se gi ki of 25 N. es be ub ct t ri k ne nd le ll load-teste usin kentledge. Th test load applie to 1.50 225 337.50kN
GROUND BEAM ANALYSIS
designed to cate or bendin moment to an bottom of w f 2 / 1 0 . om engineer us simple supporte design philosophy it th us of anti crac reinforcemen over th pile uppo ts This is ve ns ti th tt p ro b ic abilit cracking over th supports ma result whic coul affect th durability of th concrete beams. it er la ve nl ke g ro u beam ca be poured in shutte moulds (B 8110 Clause 3.3.1.4) ll design in accordance with BS 8110 Part (1985). feu
30 N/mm
High-yield bar fy
46
/mm2
b=400mm, h=600m Figure 2.38 show
typica beam section.
From BS 8110 Tabl 6.1, Minimu
2.58 90.52
20.66
2.0
Factored (kN)
Unfactored (kN) 36.82
5.76
128.56
ce en conten to be 37 k g / m ?
protection (concrete exposed to sulphat attack)
59
Foundation
design
As fe iv
Substituting
8 - 1{!12
forzand
0.S7fA
540mm
fork:
bd-feu
-M
is D es ig n
l ti ma t
0.87fyA
0.87fAd)2
ed to As
m om en t
Therefore
0.87 xfy
380.20 As
0.9bd feu
IQ
kNm
87fAd
0.9bd feu
Therefore
0.9bfeu Whenfy
is l e
an
460,[eu
4 00 , t he n
5d
0.87
As
0.87x460x
460
,s)2
'':i
-14.83A,l
s:
Th ere, or
kN
10
0.95d.
Therefore
Maxi um span D ef le ct i
c ri te ri a a r a s f ol lo ws .
Cl Span Effectiv dept
20 simply supporte
z2
df"-d=Table
0.9
2.4.
/8
Pile
e rv ic e l oa d
number
10 12
120(0.9+Mlbd
U lt im at e l oa d
(kN)
(kN)
127.39
181.23
150.84
214.95
139.58
198.71
166.97
230.07
114.39
165.71
171.02
245.33
116.64
166.97
80.78
118.43
135.96
195.83
90.52
128.56
135.90
192.96
128.86
183.16
Therefore Ma im
pa
(0.55
1.57
0.9+MI400d
)20d
Shear reinforcement tr
Ibvdt\400ld)1/4
0.79-'--.::.'---'--'---....::.....-
'Y where 'Y v =
1.25.
0.25A )1/3(400)1
N/mm2
Ta le
.0.4b,.s,. sv
0.87!.",
()
N/mm2, Asv
CD
s;
100.50 0.4
0.S7 400
V/byd. Therefore
400mm
.4)400d
10
60
100.5 mm-. Therefore
Loadings (50.625
8.0)
I [ 2.875
3.475 Bea
-3 (46.08
8.0) (38.70
8.0)
I I I I I I
1111111111111111111
4.175
Beam 1-4-7-10
(53.40
8.0) (38.70
Bea
(35.625
3-6-9-12
8.0)
[I III
ension stee is
8.0)
II
Beam 10-11-1 (28.33
Bea
8.0)
-8-{4,5) 8.0)
II
1 1 1 I I I I I
Beam 4-5-6
Fig.2.39 Exampl 2.5: beam-loading diagrams
Shea stee sv
Beam design
link v = A sv x O. 87 fy v +v c
bvsv(v-vJ 0. 87 fy
bv
Maximum ultimate momen
Therefore ; ; ' + -..£.._L_ Sy
Therefore
refore
Beam 1-3 (Fig 2.39(a))
10
10
5S.265x 30475 10
70.358 kNm
kN
ea
1-4-7-
(Fig 2.39 b)
s, 100 125 150 175 200 225
DA DA +OA OAved Ad 0.23d OAved 0.20d OAved O.ISd+OAved
aximurn
nmat moment
10
SIAO
Beam 3-6-9-12 (Fig 2.39(c)) Maximu
timate moment
46.7 4.17 10
81040 kN
Foundatio
design
Ventilate
'.r=-----.,..., 2T16
'_":":"
centres
voi
-_ :.----~-----;
50mmconcrete oversite on 1200 gaug polythen dpm
cove to link
..
',~.
<0
pile ~.
0m
75mm projection
.1:.
2T16
c ov e
to link
Concrete or stee tube pile filled with concrete
400
Fig. 2.40 E x m pl e
Be
.5
r o n d beam detail.
10-11-12 (Fig 2.39(d)) u t
N m
10
M a x i m u m shea stress /m
Vc
36 33
li
N/mm
th
119 mrn?
Beam 11--8-(4 5) (Fig 2.39(e)) aximum
0.46
400x540
sv
3. 75 10
2 k
Exampl
2.
Beam 4-5-6 (Fig. 2.39(f)) R.
29.0 p pr ox im at el y
5 0 kN
be be
_Q2_
57.67
2.875
be 2.25 Th
R.
55.74k
Rb
41.70+(57.67
2.875
in
192
4-
ie
S+C/2.0 Where
kN
1012.50kN;
kNmm; ig
lOmm);
__!!__
81.40
bd fcu
T he re f r e
l ev e
A.=~= 0.87 fy
62
10 x30
r m f ac to r 81.40xl0
0.023
se pe bl w. Therefore:
0.95
S=---=-----=3.39 =397mm
Ru
mm/blow
Pile loadings 2.5.
Suspended in-situ concrete ground floo
hammer (Banut type) Transfer
energy
200mmslab
4.70
Stu
0.50
partitions
Hammer weight
Total
(tonnes)
Ha
1.50
5.20
e r d ro p (mm)
300 1.50
0.25
3.0
0.55
External wall
400
n fa ct or e de (kN/m2) 102.
4.0 5.0
mm brickwor
2.25
10 mm blockwor
1.25
Plaster
0.25 Total
LOADINGS Part
Roof
3.75
wall
21
30 pitc
l oa d
br ck or
P la s e r
4.50
s id e
0.50
Unfactored (kN/m2) Concrete tile Ba en
an
impose load (kN/m2)
0.55 el
0.05
Trusses
0.23
Insulation
0.02
0.75
Ceiling: plasterboard
0.15
0.25
1.00
1.00
Total
Firs floo
ea
l oa d
R oo f a n
c e l in g
G ro un d 1.5
l oa d
(kN/m) 4.25
2.0
Firs floo nomina
d p
I mp os e
(kN/m)
2.0
0.75
l oo r
1.50
Wall 10.00 Total
iire several
5.0m
oo
2.25 Th
an
c e l in g
0.63
Firs floo
type)
'0 a: ( 2. 25 ) Ground floo
8.25
WallB
ecas concrete
et
42.33
r ou n
2.0 oo
5.20x2:Q
2.0
Wall
1. xO.6pO
1.50
2.0
13 00
2.0
2 2. 5
Firs floo span Total
47.97
8.10
blow (assum
Party wail Firs floo
0.75x
x2 2n.0
2.0
Foundation
design 0x
Groun floo
16.20
1.60
4.25 10
46.818
Total
Wall
Underbuil
an ground bea
10.00
226.23
Beam shears
Total
Beam
andD 42 33
Ultimate shear
PILE LOADINGS
lA
(kN) 148.155
x~
33.00
Pile (42.33+ 8.25)
5. +(47 97+8 25
4.25
Total
=245 60 kN
Pile
181.15
BeamB 47.97
Ultimate shear
Pile (47.97
8.10
4.25
lA
8.
238.30kN
(kN) 142.71
4.25 4.25
27.54
Total
Pile 70 95
16 20
4.25
170.25
370.38kN
BeamC
Pile As Pile
245.60kN
Ultimate shea
(70.95
lA
16.2
1.60)x 4.25
266.15 kN
Pile As
il
438.00kN
lt
BEAMS
18
k=.....!!._=
jearn moments
bd fe
42.33
lAO
10 5.0 10
Total
(kNm) 148.15 33.00
A.
Nm
factor 10
0.87x460x390xO.83 iv
20
im
he
18
kN
181.15xl0 0.119 400 390 25
Therefor leve ar
BeamsAandD Ultimate moment
te
ba
0.83 1398 mm
1571 mm-)
181.15
BeamB Ultimate moment
47.9
lAO
4.25 10
8.10
1.60
4.25 10
(kNm) 121.30
23041
L)
C\I
BeamC Ultimate moment
64
70.95
lAO
4.25 10
(kNm) 179041
Fig. 2.42 Exampl 2.6: pile layout
46.818 226.23
Beams
'tW~·'~1
looA, b,d
90
(kN) 148.155 33.00 181.15
Z.
v,
Because (v sing T8 link
P4
00 1571
Therefor
;r-'
18U5x10
Shear stress
39 1.0
0.64 A) is less than Tabl 2.6)
provid
nominallinks
to beam
:.
-+-(".,.,~-
1--
40 rovide T8 link at 25 mm cent es fo ul length of beam
Fig. 2.43 Exampl 2.6: line load (kN/m)
(kN) 142.71
2T10 5T20
27.54
TS-200
.1
170.25
TB~ 00
TS-200
TS-250
1.0m
2T10
'I
5T2D
ST20
)6.1 kN 5.00m
P'
I_
5.DOm
15kN 2Tl0
1.2Sm
1.2Sm
2Tl0
4T2O
., T8-200
T8-2S0
T8-2S0
T8- 200
14T20
tT20
~::;
4.2Sm
4.2Sm
BeamB
2Tl0
C\J
-.i
BeamC
Fig. 2.44 Exampl 2.6: reinforcemen details.
65
Foundation
design able 2.6. Sh ar st es
usin T8 link (kN)
Tension steel
As
Spacings (mm
Vc
175 130 135
100 185
220
200
230 236
3T20 0.57 1470
3T25
153 251 182
BearnB
Using T8 links
ltimat mo en bd
144.71 kNm
ltimat sh ar
k=0.86
uppo beam.
Therefore 144.7Ixl0
170.25 10 400x390 40
Therefore As
0.60 us nomina link throughout beam's tr
li
om nt
226.23 kNm
ltimat shea
266.15 kN
226.23xl0 bd
feu
400x390
x25
0.76 10 0.87x460xO.76x390 se four 25
bvd
40
266.15
ba
1907
to an bottom (196 mm
x19 39 10
400x390 therefor design link required
66
or emaining length of
Berezantsev, V.G. (1961) L o a d bearin capacity an deformation of Proc Fift internationa Conference on Soil Mechanics, Paris, Vol. 2, pp 11-12. 1) 6 3 Concrete in sulphate-bearing soil and groundwater Building Research Establishment.
1.09 N/mm
(Ve
ltimat
5mm nd then tw le T8 at250
BIBLIOGRAPHY
39
Ve
ac
(1.25-0.68)
1078mm
Us four TI to an bottom
looA bvd
400
144.71x10 =0.095 390 25
feu
0.87
loo.50xO.87x460
170.25 kN
Ve
0.68 N/mm
capacity of piles summary. Sol (Soils), (18/19),21-31. le ld BS 1964 BS648 Britis Standards Institution. Structural us of ason y. inforced masonry. BS (1984) BS 6399 Design loadin for buildings
ia
Institution. BS (1985) BS 5628 Structural us of masonry. Part 2: Structural us of einforce an prestresse ason Britis tandards Institution. SI 1985 BS 8110 Structural us of concrete practice fo design nd construction Part 2: esig charts or singly reinforce beams. NHBC (1977) NHBC Foundatio Manual: Preventin Foundation Failures in Ne Buildings National ouse-Buildin Council, ondo no ew itte as NHBC Standard Chapte 4.1) Tomlinson M.J. (1980) Foundatio Design an Construction, 4th edn,Pitman. Vesic, A. (1966) Test on instrumented piles. Ogecne Rive Site Journa of Soil Mechanic an Foundation Division American Societ of Civi Engineers, 96 SM2.
3. ' OO m
fr
length of
sformation of
bearing soils
bearing
er
id io ad eq co li ti take plac an it ma take severa year before it finishes tt in ti le at ly id ed ay il cl soft alluvium an clayey peats.
INTR DUCTIO
oundations transmit th tota load from building on to th ground by direct contac pressure he foundation us disth bearin stratu is no overstre se an that tota ettlement ar within acceptable limits Th foundation designer therefor need to have so knowledg of th type of strata presen belo the foundations it ig io ea ll in ac ty im le is is ca ar at
arke volu etri change as thei oi ture conten is changed. Clay whic fall into this category ar referred
they ca occu in othe area in localize pockets. different properties. Cohesive soil ar subjecte
to plasti deformatio
when
can affec cohesiv soils with medium-to-hig
tg materials,
1: Unre li
1:Co of tandards
Structural sn Standards
charts fo Foundation
Council,
surface subsidence. ap
ac
ty
th
e,
swelling take place. detail in Chapte 6. er lo er
capacity. lo il ca ai ta ea th it buildin ca accommodate safely.
plasticity
tree an vegetation ar remove
ed
cc tl
hi subjec is deal la
co
it in
in
or te
af th ti
actual pres ur belo th foundation an th pressure from em ip ed when designing buoyan foundations ..
struction, 4th
ll co tr io ti case of excessive settlemen aris because of unforeseen soil conditions whic suddenly arise. examin th type of ground ovemen echanism whic ar potentia causes of settlement in cohesive soils. (a Consolidatio settlements. In cohesive oils whic ar saturated, th effect of loadin th soil is to queeze ou
in
istu
ll
cl
to
in
consolidatio stresses occurrin becaus of th increase in effectiv stresses. ch ca au ev heav in sustaine low-te perature conditions Mo ilts fine ands an chalks ar frost-su ceptible Grea care must be take when designin foundation fo cold storag buildings.
4.1).
~ive Site. American
al ed
(f)
existing foundations. In effect th clay ar subjecte to shear-slip type of failur simila to that experience on slopin sites. (g inin subsidence Settle en ca occu at th surfac
cr wn hole olla se in pill an stal wo ki s. This subj ct is co er in more detail in ha te ferentia settlement must be kept within reasonable limits 3.
ONSOLIDA IO
Fo foundation on clay soil either of th abov criteria ma govern th foundation design
SETT EMEN
Ther ar tw type of settlement mmediate settlements. Thes
cc
within se en ay as In cohesive soil th ultimate bearin capacity is calculated by usin tota stress parameters As settlement in such soil take longer to develop, this give th fina construction case whic is th most onerous. an allows th foundation design st easily obtained at no grea expense. wher th
ecause they cc apidly an ar elativel small, they seldom pose problem. Consolidatio settlements. Thes ar time-dependent an an ta ro severa nt to se er year to evel (usually 1-5 years). Consolidatio
settlement analysis is applie to al saturate
strength ar derive from Coulomb' equations:
sa ficien of compressibility m; from consolidatio test results. Th values of m; vary as th pressure ranges vary From th pplied ertica st esses, th verburde ressettle en ca
'predi te
c'
1:
crtan125'
where 't shear strength. c' cohesion (kPa). normal effectiv stress componen (kPa), an ~'= angl of internal friction.
sing th m; values Despit
bearing capacity.
sc and-fast rules for settlemen computation. he desi ni undation on co esiv soil ther ar
Allowablebearingcapacityq. Usin th it =0
separately:
100
10
40
tl 'iii 0>
~~
30
Nc/
25
::
(I
200
.,
35
·c
erza hi bearin ca acit eq ations fo
-:
Nc
-e-
sa et
andnet ult
quIt
45
q~ t:
actor
20
»:
'0
L/
. .. .
~y
15
10
Nq/
-0.
.2
.3 .4 .5
Fig.3.1 Bearingcapacityfactors Forsands,c 0, thereforecNe Forclays, 125=O.givingN O.N
Ny and
and Ny (afterTerzaghi). and Ny basedonSPT valuesfor 125. 1t =5.14. 1.0,Ne=
10
00
200
soil
Consolidatio
nabl limits.
Deep foundation
wher undraine cohesion, bearin capacity factor tota overburden pressure at foundation level. he 0, 5.14. 1t
(0)58)
q« which
teria ma
foundation base this wa applicable to shallo foundations, i.e. where zl is le than 1.0. Fo stri footin Terzaghi's equatio is calculated s u c h soils .; tion case atio design
-ValuesofN
;E
N;
'Y
0.50 'Y
(I
r/.
10
al es increase to 5.70 fo
to
OJ
.E
"/ 'it.
10
to
~,
ff 'Y
The coefficient
,le
normal internal
Surface foundation
VI
-0 .l!!
Therefore 5.70
Shallow foundation
(0=8)
0.
he al es and Nl ar obtained from Fig. 3.1. Th valu of
quit
Ii
10
li
Nl
I)
"0
to
qu
settlement
al ow
th
char
ects ar in
(a
10
foundation, B. 0, 0, N; 5.70 an 1.0. Skempton showed that N; increase with foundation dept increase fo from Tabl 3.1. Tabl 3.1. Nc values fo dept factor in soil with Skempton)
60
0>58)
(after
V, Z/B
8040
pf
50
Deep foundations
Surface oundation
10
type
5.9
30
10
Angl of shearing resistance 4l
9.0 7.50
'I
.9 '0
Usin thes coefficients th ultimate ne bearin capacity tr in en qn
0.
Fo qn
'Y
Nl
/1 1/ 'm
square or circular foundation 1.2 N;
Po (N
1)
00
'Y
1.
0.8 0.6
Ny
where th bulk densit of th soil belo th foundation th undraine shea strength of th soil th effectiv overburden pressure at foundation level, and the foundation width (o diameter) he ultimate bearin capacity Puis give by P u = P nu
II
OJ
+p
where th tota overburden pressure at th foundation level. then th valu fo th densit us be th submerge density. When calculating o, th wate tabl is at or abov th foundation level. Meyerhof (1952) modified th Terzaghi equation to make allowanc fo th foundation shape, dept an roughnes of th base alue and .m
0.3 0.
(b
{I Angl of shearing resistance
4l
ndN fo stri footings (b values of Nl fo stri footings (after Meyerhof 1952).
Terzaghi formula, th
ub erge densit must be used if th
cohesive soils i.e, ~= 0, of N; an ta en g. capacity qa is iv
O.Therefore values
si
stri ooti gs ca be obtained strength
Shap factor
~~
~~-+--t---l
3. .2
2~~--+-~~~~~~--~
3 ~ - - + - - + - t I - l- t tl + - l - H - I \ . . .. . .- t- - -
si
th
nd aine shea
Ve tica stress distributi
When foundation load is applie to soil ress re ul is generated. Th stress on th ground decrease with dept an
4~+-~~-;;-~H-\~
5~~--+--H~-'~~~--
obtained from Tabl 3.2. Table 3.2 Vertical pressure factor
s:
7 ~ ~ - - +- - H- + -H - r~ - i +- ~
BIZ
Factor fo rs
Factor for vertical
0.032
0.065
9~~--+--H~-H-+~~~~ uried footings
0.1
.p
° 20 1
.p
° 1
strip
.p .p
( ci r l e 30°
1.0 1.50
0.25 0.30
0.55 0.71 0.82
3.0
0.29
4.50
0.23
7.0
0.17
0.92 0.94 0.96 0.97 0.978 0.985 0.988 0.99 0.991 0.994 0.996 0.997 .0
Length/widt ratio of rectangular foundations
Fig. 3.3 Values of shap factor Meyerhof, 1952). Bearin
fo stri footings (after
capacit
factor Nc
10
_~
1\
0.30 0.358
contractpressure; foundationwidth;Z depthof soilelement belowfoundationbase. Shearstress shearfactor Verticalpressure verticalpressurefactor
"0
Theoretical
Experimental 4.0
Fig. 3. N, values fo stri footings on soil with 1952).
(Meyerhof,
where Nc bearin capacity factor averag undrained shea strength soil belo th fo ndation, Po vertical su soil l, fa to of safety (usually minimu of 3.0) Therefor qnet=N
Fo st ip footin therefore
6.50 fo zlB
0.75/0.60
1.25;
clay sites
Some clay soil ar very variable They ofte contai watersi glaciation he thes ar encountere in an excavati n, many building inspectors as th roun wo ks fo eman to excavate eepe in th op of fi di clay at lowe level. Quit ofte excavating eepe ca lead to costly ound ti la distance an th sand ar water-bearing, or contai perche water, th si es of th trench will collapse an larg soft
6.50C qUlt=~=.
excavation an fill it with mass concrete to within 90 mm of th ground level.
Sinc th bearin capacity factor N; th {) then reasonable ne allowabl bearin pressure fo shallo
foundation or wide reinforced stif ground beam
Consolidation settlement Tabl 3.3. Correction factor
ed shear
(kN/m2)
1.2
,/-;
150"'\.r '110'
tiepth an
Very stif Stiff Firm to stif Firm Soft to firm Soft Very soft
'V,vertical
Tabl 3.4. Proposed allowabl bearin values fo clay (after Terzaghi an Peck (1968»
.'e
;~
100-150 75-100 50-75 40-50 20-40 <20
Description of cla
oi
ur
Very soft Soft
Very stif th
he
ng
di on
un tabl
lope coul
qrn
15-30
24-48 48-96 96-190 190-385 >385
64-128
107-215 >215
260-515 15
f'Av--t(:<
l~
(IV' Vt,-y
clay soil id isplaced at dept belo ng ow th of
ground leve la ha ng
it of ls ou ti he th dt used is acceptable to carr line load of 60 kN/m alon it length Usin Meyerhof values fo c, for I'l 0:
ent
5.14,
1.20
1.0, Ny
Therefor ne ultimate bearin 308kN/m
are suspected.
in water-
v"wation,
Actual pressure deductin nc
Chec at 2.
th amount obtained thes
in-situ
oerched calculated stre se at foundation leve an in th stre se ow th
ou
ti
hi
ur
bu
levels
bl
1c 1.90SIl, neglecting
overburden
pressures.
5.14 Cll
le 3. equals 0.55. Actual pressure
~~~
103 kN/m2
60 kN/m depth:
Allowable bearin pressure
large, soft
capacity
factor of safety of 3.0:
Allowable bearin pressure
.ilt of pa
'mmof
32--M
27-54
esult.
stri ooting 1.00m of ne ir ow
w,;;rlevel.
Strip,
13 50
<2
Exampl 3.
I,
Square
numberof blowsperfootin standard penetration. cohesion(kN/m2); qm p r o p o s e d normalallowable bearing value (leN/m2); factorof safety withrespectto b a s e failure
operations are
especially if majo cut-and- il
1.0 0.90 0.75 0.65 0.60 0.55 0.50
ti
1~~ or 33 kN/m2,
zlB
1.0/1.0
1.0
51.50.
Cll NJ3.0 Th safe bearin capacity overburden pressures yz Therefor at 2. m, safe bearin capacity 51.50 8x 87.50 kN/m Should ground ater levels rise thes pressure should be halved. Th widt of the foundation is therefor satisfactory
.3.5
Sett
ts in
il
di on settle ents square pa
bl
houl
al ay
be conservative
Basi settlement calculations
comp essibl oed
my
where
Poed
stratu
of thicknes
oedomete
settlement
m;
1.0
coefficien
of compressibility.
Th
Dense gravel dens sand an gravel Mediu dens gravel or mediu dens sand an gravel Loos gravel or loos sand an gravel Compac sand Mediu dens sands Loos sands
(600
Very stif boulder clay an hard clays Stiff clays Soft clay an silts Very soft clay an silts
300-600
relationship
Co ment
m; and E, t h
where Though
m;
relationship
betwee
m; and
de
less than belo th base of the foundatio
>300 100-300
'k'
'i,j,
lu
''''''J'', ~._Poed =H,
le
lc
"z
te
V" H'
ll th la +H2 v2
+H3m
"z
150-300 75-150
,co settlement
Not suitable
ection factor
.>
r rr r , ., . .II"I ,
'~'
: : . . ,. :~ :: ; z " : : ' . .. . . - :: : . : : ; . <>
."
)1
rrrrr1 -'-1 r - T ' 1 " " " " I _
'·t::·..:.....
••
:
•
J
__
..........
72
Tota settlement
od us
(1+v)(I-2v)
my
<200
g'
(I-v)E
Widt of th foundation no less than 1.0 Groundwater leve assume to
2 0 0 -6 0 0
betwee
Foundation loa
Fig. 3.
imposed
Schmertmann.
Allowable bearin valu (kN/m2)
fs
(rnm): 0",
0",
Tabl 3.5. Allowabl bearin pressure
Cohesive soils
io
foundations.
(a
Noncohesive soils
ti
..
'.
Consolidatio ~OkN/m
p:=
Pood
Flexiblesquare foundation
total that settle
settlement
clay.
of uc guide.
ii kn
strata.
'" impose ssibility,
ic
pp xi
t ho d
va la le
or
c u t in g
th
ot
analysis lard tables
's modulus
:ed soil) lisplaceelastic, th ,.~ relevan
58'~---+----4-----L---~--~
Fig. 3. Vertical pressure unde foundation.
1.58
uniforml loaded square
1.678
(b
Influenc
in /a tors
etho
over it factors. As m; e c a se )
consoli-
I)".
cor-
Fig. 3. Stri footin on unifor distribution.
soils: vertical pressure
he
equals
belo
O'z.
th
ooting
ts
be
ZI
and
Z2
(variabl
depths
Fig. 3.8: Pood
whic
le
O'
where II and
[ I )
and
Z2
respectively.
1.50B
16
Bm O'
0.50
Poed
1.67
belo
th footings
0.835
mm
2B
h ou s un at on 60 po h re e t o ab l . h e p pl i ne lo qu ls k N/ m n . ne lt take at variou depths in th soil directly belo th footin indi cate that ther is stif desiccated clay crus fo 1.0m belo ground leve unde lain by of silt clay alluvium Th values of th vane 0m ow de th l o g ro un d l e l . t e n e t h t ot a settlements under the gable foundation
Foundations in cohesive soils
Influence factor 120
040
020
-;
1.0
1 \ ' \ .~
140
~t,.,;
,,~)
-,
Ql
r1\
3.0
t I
'iii'
-,
....
'&
4.0
Fig. 3.
Influenc line factor
at th centre of
foundation
Stress applie at footin level: Ci
600 Consider th loadin to be on an infinit footin length Th vertica stre istributio gr ph is show in Fig. 3.10 Th values pv are obtained as follows: !... 0.25
Ci
=-2-
3900
Ci
4+3 =--2-
3900
Ci
=-2-
3900
Ci
=-2-
3900
pv
!O
=8.65mm =5.57mm
0.41
Total settlemen
Therefore Pv
--2-
mm
This is le th mm an is considered ac eptabl orre tion factor could be applie where 0.55-{). whic woul result in settlement of abou 14mm. Usin th quic approximat method
=0.75 8=
0.75p
22.4
=0.835xO.60xIXI08X10 !... !... !...
0.75 =1.2
r, =0.50p=0.50x108=54kN/m
1.25
P:
0.60
2.08
1.75 =2.9
!... 2.25 =3.7 0.60
0.30p
Pv =0.20p=0.20x108=21
kN/m2
Pv =0.14p=0.14xl08=15
kN/m2
.4
Ev
compressibility, Ev
0C
lI
v)
is give by /m
Th soft clay ha an undraine shea strength of 30 kN/m Ev
Therefore
kN/m
Th tota settlement is equa to th re of th ressur diagra in Fig. 3.10 Fo an approximatio take triangular distribution Then
74
=138 .7mm
MOISTU
MO EMENTS
weathe or from moisture abstractio by root of larg trees. sl ic st evap rate ro la soil an be redict assuming th lowe li it th soil moistu conten to be the shrinkage limit. Desiccatio beyond this valu will no brin abou an furthe reductio in volume sp th England, possess larg potentia fo slo volumetric change Howeve th mild am climat whic enerally re ails eans that an significan deficits in soil moisture conten
Moistur
movement
qlQ
Or-~--~--~~--'---r-~--~~~~~--.-~~~--'---r--T--.-~---r--.
0.51--t_-+_-t-_t--f'+_t-;.
e~~/
1.01---+-+---i-['_~++--+-..y___'-+V~""-+-+-I--+-+--+-+--l---1
ij~--h./~~-f--+--+--+--+--t--t--t----i,.---J
~~---+-~~~~+-~~~~--~~--+-~---t---+---t--t---t--~--+---t--;
0°fL
2.01--+---+---I+/I-I---+-/+,-lI-+--I--I--t--+----l-+---+---+--I---I--t---t----t
zlB
4.01--4-+~-~-4-~--1--~--+_-;--~-+_-;~-+-+--4~~-+__t-_r__i
correction Idresul in
i,ffim
Fig. 3.
Distribution of vertical stress beneat
long stri footing.
0.75
trem larg
ry
trees.
0040
moisture
Soft silt
2.0m
~.
te shrinkag
day alluvium
it become
significant.
:::!'!..
southe st of etric change. prevails 'e conten
Fig. 3.10 Exampl 3.2: vertical stress distribution
75
Foundation in cohesive soil
compressible.
Activity
onsh
Plasticity inde Cla
percentage
twee
he lastic ty inde
nd la pe ce ta
100 ~80
Plasticity inde
0:
Liquid limi
Plasti limi
PI=LL-PL
60
:5'40
~,:~~~;;~~:::=======~~~i~n~:e::~~~ 20
100
a y f ra ct io n
Fig.3.11
(.1111
Clay 'activity' grap (after Skempton).
(a
Conepen trom er
26
25 24 23
s-
22
_, 20
Ii 19
c.
G)
18
16
..---
~~
15
14
50
51
Moisture content{%)
55
56
Fig. 3.12 Liquid limi grap usin cone penetrometer test Th liquid limi is the'wate conten correspondin 55%.
76
57
58
to 20 mm penetration. i.e.
Moisture movement
-me less
th liquid ;hearing no plastic ~.~failure :limit. nten withicle in th
th surface. Th cone penetrometer is placed at th centroid le t. is dept over hi test firs depres again. th
period of is easured. is repeated liftin th cone clea fillin in th io with or past an allo in th cone to fall difference betwee th tw measurements is less
averag penetratio is note an th oi ture conten of th sample is determined in th normal way. Th pr cedure is repeated at leas four ti es it increassa ples should be us ufficien to pr duce depths of penetration within th rang of 15to 25mm li li ti at enet io th ti ca ai istu al th zo ta le straight line should be draw throug th points on th graph.
liquid .st should
correspond to
cone penetratio
:::-70
.............
c:
Uqui
60
limi
r-.........
~LL iii 50
~l
40
10
Number of blow (log scale) li
io
apparatus.
.4.2
asti
of 20 mm (Fig 3.12).
imit test
ay am th
Casagrande appa at
This method wa superseded by th cone penetrometer bu it io ugh-
___ ough
groove is cu in th to of th sa pl usin tu
is
2mm specia rofile
at
lo ap er 3mm conten is determined in th usua wa (Fig 3.13).
ev/s
t--...
\t
it ee as la
le (b
le paste. and elled .off at
........
ie ci
to
ed tw en lm th he sa pl is said to be at it plasti li it when itju
e. begins
te th is te es ea several times. Once th soil plasticity characteristic have been found. th clay ca be classified by usin th Casagrande plasticity char (B 59 0: 981) hich will enable co parisons to be made.
tu (a
Ca agra de plas it
ha
plasticity inde an th correspondin te then as
liquid limits ar plot ts it
Rubber bas (a
13 mm
~C
(b
(b)
a pp ar at us ;
zero an th liquid li it is 20%. he ai oi type ar give pecifi designatio io al le erin to gradin an plasticity (Table 3.6)
( b g r o vi n
to l.
contents ar plotte on th vertical scal agains th nu be blow on th horizontal cale sing lo scale. he oi
letter
Th triaxial test (undrained compressiv test
hi test to determin th values of th tota shea strength ar er is ar ie in tr es atus bu th sample is prevente from draining during shearin an is therefor sheare immediately after th applicatio expresse in term of tota stress tw components cohesion an frictional resistance. Samples
i.e.
limit, expresse as whol number (Fig 3.14).
Uppe plasticity rang Low
70
50
High
Intermediate
tt symbol of an ateria containin significant p r p or t o n o r a ni c a tt er : .g MH
CH
40
'"
(cL)
30
r-A line
-:
.\:
iii
Extremely hig
Ver hig
PI
0 . 7 3 (LL-20)
10
-
40
10
50 Uqui li it (%
80
100
90
110
20
(C)
line.
compressiv
Table
tests, usin thre specimen 38 mm in diameter
3.6. Casagrande
Coarse components
classificatio
in
latera pressure of 70 140.an 21 k N / m 2 at constant rate of strain of 2%/min he th re ults of thes test ar available, oh circle of tres ca be draw hich will enable values of be determined
Ex
Sand
Tr
ra Uniform
Pu
Ga
Pg
graded
A dd it i n a
a xi a s tr es s r e u ir e
f o f ai l r e" ,
Mohr circle
c,
ic
Fine components
rt resistance,
is !p
(Fig 3.17). r e t ri ct e
l as ti c r an g
C~ plastic)
(II
(kN/m2)
al-a3
stress, at
130
340
70 f u incorporatin
140 groups
210
I,H,VandE 70
53
123
140
72
212
210
86
296
Bibliography
03=70
heA
01 =340
..s.anr rate
and
~I
j!j
circles dc
Shea
stress
st gave .sures of lohr circle on th
_____. __~~e
fictional
line drawn
Normal stress
rincipal
BIBLIOGRAPHY
Geotechnica
Engineering Handbook Pentech
Press. London
it B ri ti s
t a d ar d
I ns ti t t e
of te purpose, Britis
Standard
Institute.
ti
Casagrande,
A.
Proc American Societ of Civi Engineers. Approved Documents HMSO
London
79
Meye hof, G.G. (1952) Th ultimate bearin tions. Geotechnique, (4), 301-332
capacity of ounda-
Peck R.B. Hanson W.E. an Thombum, T.H. (1974) Foundation Engineering, John Wiley, Ne York ouse Builder' Refe ence Book ll 97 Newnes-Butterworth, London.
80
Building to 51 it la Research Conference, Institution of Civil Engineers Div. 180. Terzaghi K. an Peck R.B. (1968) Soi Mechanic in Engineering Practice, 2n edn, John iley ew ork. Tomlinson, M.J. (1980) Foundation Design and Construction, 4th edn, Pitman
';'6
Chapter
ineering 'ion, 4th
particle tend to be abou th same size th curv on th char hows larg percentage of larger an smalle particle with only smal fraction of theinter mediat size then th sample is deemed to be gap-graded
Sand an gravel ar classified in th laboratory by carrying ve est. th es th es ar d, il
ig ll siev analysis: ticu ar ar icle ze he pe ce ta of ar icle larger or smalle than an particular particle size be
el
ad
if
I. 2.
ze
ga un
ra ed rmly
ra es th
rv
ee
es
el ed an
ur ravels laid down in th form of alluvial depo it ar usuall ixed with sand in variou proportions. Tabl 4. list th
ciencies of an particular size of particle
composition.
Britis
E(')
..:;co
10
('\10100
E~
E"":N
-e--
Standard Siev
c?
Size
,. . ,. .
(\I
N~
(')1
COr-
1/ (3)/
(1
2)
".
"../ f.I.ITI) Clay:
Fig. 4.
20
20
600
60
200(m m)
Fine Silt
Sand
Particle size distribution chart. Sample 1:gap-graded sand gravel Sample 2: uniforml graded sand Sample 3: fine silt sand
ra Tabl
4.1. Required descriptions fo composit sand an gravel
in-situ
Slightly sand gravel (grave with little sand Sandy gravel (grave with some sand Very sand gravel Sand/gravel Very gravelly sand Gravelly sand Slightly gravelly sand
Fi
5-20
sand
20 sand 50 sand 50 20% gravel 5-20 grave 5% gravel
sand an silt ca
xhibit dilata cy an in soil with
site in ecidin whethe
si pl th
articularl
soil is
when
enet om te shea va test so fiel Ther ar simila ty es of quic fiel test fo sa ds an gravel bu th relative densitie ca be assessed by (a visual examinatio of th tria pi or excavation (b an di gi with spade, ic ar sh th se st pits); Cd)standar penetration tests.
4.2. Ve
Fiel
reasonable
ensity assessme
lo se Side
trench collapse whilst exca atin
in
examination.
il approximatel iu
Tabl 4.2. Fi ld ex mination of ands an
inspecto s,
Thes fiel test method ar crud bu they give guid as to th soil's variability.
su ls conventional well-pointin systems. th fiel soil ca checke or il tanc by sm le su sample. Difficulty ca aris
gravel
st so engi eers an buildi wate is present. cohesive soil si pl
500-60
0mm
mm into th stratum. ss le
iv 15 mm into th ground
ilts
Fine sand visible
visible
th grou d. rock.
he mate ials av th consiste cy of
soft
Not dilatant Easily crumbles an 'sh whe dried s g
ep
dt crumble
s g
s s
Non-plastic
Plasticity evident
.1
50 mm squa flat-bottome wooden pe is rive hand into th ormation or ap ro imatel 50 mm an an ssessbe th if ty experience in th driving.
.2.2
Visual bservation
Th visual observations made during th tria pi excavation se la iv granular soil Th followin factor should be applie in th assessment.
coral-lik stratum. in-situ qualities, bu nc disturbe an ex osed to flowin wate se deteriorated it is highly unstable an of this calcareo
s.
so ss compoten strata belo
se ld such sands.
la
collapse during th digging, this indicate that th soil si settleme ts co ld result especially in we ground Such ro nd im rove ent. If th lo se conditions ar ot to eep, th soil ca excavate an re lace in discrete layers usin suitable vibratin trench roller
~~OILS
and
2.
ls i..]
when
us
in
th
ti
be
ng ca
ty
3.
me test Hole fo to my ba
fo sand dby: subsidence.
etrometer in tria
avoi
excessiv
settlements.
.onable
rvating. -ended
.2.3
ro
te
ve
~H---
SOmm
Open cutting shoe
50mm
I l pick '"vr
than should be halved
8004:1986 give
Table
th
densit
classification
hand assessclifficulty
.2.4
Th
ta
rd
tr ti
apparatus, showing drillin rod, split barrel sample cone shoe.
Tabl 4.3. Relative densitie of ands an gravel ba ed on results
values.
86
Fig. 4. and
60 cone shoe adde fo taking SPT readings
Relative density
te
Very loose Loose Mediu dense Dense Ver dense
N, blow count/30
mm
<4 4-10 10-30 30-50
lI....avation
;I
IS te value.
IS
it ides 1e soil allowable p"cessive
di regarded
Fig. 4.2) values.
Such high bt ne
Iiscrete
gr el
us ba
th on
ts
io
values will result
the
Foundation in sand an gravel Correctio
factor
corrected measured
14
value value
......
13
10
12
20
r-,
11
40
""0
II
a.
50
60
Very dense
70
Relative density
l'
'iij 40
Dense
50
'\.
'J
>.
a.
Medium dense
30
;:(10
~100~------~Yr----------t----------1
Very loose Loose
'E
ID
:>
30 20
150~--~L---1-----------~--------
10
~.
.:./ Angl
of shearing resistance Ijl
ig 4. Correlatio of values of e, Peck, Hanson an Thornburn).
and
with SP test (after
250L---------~--------~L---------~
Fig. 4.
Depth-correction values fo SP
vaiue (Gibbs an
Holtz, 1957)
al estimated, an correction factor were derive by Gibb an accoun of th overburden pressures. lt at il al estimation of th relative densit an modified ca be obtained from th formul
value,
=15+.!_(N-15)
where N> 15. 4.2.
te pr tati
15the no correction is required SPT results
Terzaghi an Peck (1968) produced correlations fo bearin obtained from standard penetratio results. Figure 4. illustrates th factor and N.., derive by erzaghi, Peck an Hanson usin th angl of shearing resistance In addition, .a
ti
es
0m ic
However, w h e r e th bein used in sand th allo able bearin ca acit us be checked, as research ha show that thes reduce rapidl an bearin capacity failur become th criterio with suitable.r factor of safety applied et at ig an as on differen ratios of dept to foundation widt an ba ed on 84
.0
Footin
widt
(m
Fig. 4. llowable bearin pressu es on sand base on SP value (2 mm settlement criterion)
straight-lin relation hi fo si plicity. hese values ar ls an ed ater levels rise to ithi distance equa to th oundatio width, then thes values should be halved 4.2.
Ulti at
earing capacities
pressure is usuall fairly rapid, th effectiv shea strength
Relative densitie of granular soil ~rv
loose
650~,--------.--------,--------.--------,
:;se
~",Jium dense
N=50
5401~-------+--~----~------~--------~
N=40
)r nse
~4301~-------+~------A--------,--------~ Itive
lsity
e. 'iii
N=30
0-
~3251~------~~----f-----+-~------~--------~ C)
N=20
215,~--~L---*---~-----h~-------+--------~
'a (after
zl \.'£, 'foundatio
'"
widfR,
(mm)
1200
900
1-
I.
.l,.,(,('
o un da t o n safety
se le en
n o e xc ee d n g
1.0. Fo
25
2.0.
65,lli--------r-------.------~------~ N=50
6501,----.----.------.------,--N=50 N=40
'"4301r---------~--~----~------~--------~ N=30
:t:
~3251r_------~~------_r~------~L-----~
N=20
£2151r_-----+~--~~--_hL-----~~------~
:".T
108J--I--J.~L~~4:~::=::==I=====t ihould th
N=5
oundation
90
600
Foundatio
width
(mm)
zl
rengths
108
foundation
settlement
no exceedin
25
N=5
1200
Foundatio
width
0.50.or 2.0.
foundation
settlement
no exceedin
(mm)
1200
0.25.or zl 25 m . F ac to r a t s a e t
2.0.
85
an 45 /~
40
-Go
ii c:
til
35 30
25 ....
20
.
v/
-~--
.......
'0 Q)
"Ol15
.&
10
v-
.,., i--" q/
.4
Fig. 4.
Tabl
Bearin capacity factor Ny a n
1.0
100
fo sand an gravel strata Ny and
values base on SP
200
values and j1j relationship.
4.4.
SOILS
Value (degrees)
Loose Dense
27.50
33
27-30
34
45
30-35
Granular depo it ak good founding strata if they ar in medium or dens stat of co paction. In fact such ands an gravel perfor better than firm clay in that th foundation settlement occur immediately they ar loaded granular deposits have water-bearin levels either in th form
ar used when considerin th allowabl bearin capacities Becaus of th difficulty in obtainin undisturbe sample in th el or or te in ou ng ar
belo th wate tabl will caus instabilit in th ides of th excavation In addition th base of th excavation ca 'boil' nd er lo an ar to
various correlations.
ma be possible to contro by pumpin from lowe ump. er ti gi to ec of em ra ly
capacity of
shallo
foundation is give by
Strip footings nu-eN
+r;
locality an result in subsidence of existing buildings.
-1
Pad foundations nu
1.
where
N;
may
gravels. P« (N
1)
0.
trengt of th soil of th oil; the foundation width Po the effective overburde pressure; c, and ar Terzagh bearing capacity factors he th soil ar granular an zero, eN an le te and base on l/ values.
throug
water-bearin
granular soils,
el pointing ca be
th shea
"(= th bulk densit
86
particle as occurs
he pu ping from open su ps Wher
lt ll in in itab et te lowering an it ma be nece sary to us electro-os osis Of ground-freezing methods
ou Tabl 4.5. Factor
variou circumstance it will be necessar to consider usin ,dr formation. piling is used it is pr er le an re ec no ic to us precas concrete driven le teel le ha or pile th te asin lter ti el n-
nu
(from Terzaghi
nd Peck)
SPTblow count.N
Angle of internal friction, l:'l (degrees)
lO
30
30
36
18 26 37 55
ar eviden at depth.
72 ~
~
e4 allo le ar ca acit of an la il is ally limite by settlement considerations Th allowabl bearin settlement of with ,nofactoI:s gf safety included for. .They re al base onthea sumpti6n'tha th wafe tabl is ata ep ea el nd ti as
For foun(iations l:ss than' ~.O.~~~.peatj~g capaCity should be""checkeci wffi ~eirigappUe4agamst'1)eaniig"Capacity"'Iarrure~~'"
LAR
acco panied by high settlement
an rotational
most structural failures an to a~~~'ii~Cturr~';lcesiiie (f es ed to ee ot ettlemen within acceptable li its. In ua io er ds re 'Yaterlo~
foun:dati;;~o(
Id and nmdation
when ~le for
obtain jl
le
and an ab
er ed
za hi
xcavation
for
fact'\?ry,..i ~ 5 0 ' 5~kN Per"
'),
wide Th maximu re run. Fiel st ha
with averag .20m de th Dete in he lowa le ring ress re nd chec th foundation widt if the,depth of th foundation is 1.20 belo ground Bulk densit of soil,i 18.0 kNho FrolI\ Fig. 4.4, '';' 30 an N y '; ' 3 0 . Therefore (netult)=
'Uearrng"capacity generall
strip footin
'1
Nq O)
where and are bearin capacity factors; dept of foundation belo ground level; foundatio width; 'Y bulk densit of soil belo foundations. Therefore' q(
ult.)=
30 (30-1.
0·60'18XO.
=(15+23.20)x13.50=51 515/3.0 170kN/rIi Actua bearin pressure
55:010.75
kN/m
13 kNho
ofthe ,1 'boil' heavy it sump. uporarily .wering
may injection s.
D,
installed Water table
g. This
ne Where urndwater iosis or
0.4
.3L---------~--__--~~---0.5
__----__~~~_,--------------1.0
Dl+B
Fig. 4.10 Correction factor to SP blow coun fo dept of wate tabl (after Peck Hanson an Thornbum).
Tabl
is he un le ul ul in he ow le ng it ng al th is ui bl iz foundation whic will keep settlement within acceptable limits
;''f
settlement where
," ,"
ve bu de
(degrees)
pressure
18
SP blo
1.20
From Fig. 4.3, correction factor
10 15 20 25 30 35 40 45 50
count.
21.6 kN/m 3; therefor modified blow coun
N' isgiven by
N'=3
um un up nd io correction factor of 0.50 from Fig. 4.10 Then
5.13 6.50 8.34 10.98 14.83 20.72 30.14 46.12 75.31 133.87 266.88
\''''Y
J.,\
applied bearing pressure
4.6. Typica bearin capacity factor
le
ap ly
;'\ll-" ( ( \ \ A f r rt(\!-
bearin stratu it sand alte nating with ne id bo to la of B283 as required in BS 8004
firm
in
\";H't'f
em nt
0.10 1.22 2.65 5.39 10.88 22.40 48.03 109.41 271.76 762.89
1.57
2.47 3.94 6.40 10.66 18.40 33.30 64.20 134.87 319.06
(~
.:
p=
1.0
Exampl
~~
4.
0m 0m 18.50 kN/
foundation sand if th 12at 0m Conside continuous 18.40:
category Th valu of shearing resistance
level. etermine th ultimate bearin capacity of th soil strength parameters ar base on SP result of th an 15at 0m th that jl I> footin with jl Ny
be in 0x
Safe bearing capacit qunet=rZ Nq
-1 Sq
q=
+r
3.0
+0.5rBN
pe
dept factor
32
(B/L) tan
1+
I>
(fro
529 kN/m2
acto of safety of 3.0: 529 =+r 3.0
De Beer);
sin < 1 > ) 2 (z/B) for z/
I>
Sy shape factor
Appl in
Dy
20
1.0;
176+ 18.5
B/L;
Dy dept acto 1. Usin Tabl 4. or I>
or zl
1.0. q = 33 .3 0
48.03:
pruden to halv this valu an us
1. figu
194.50 kN/m of93 kN/m
Sq =1+~tan35=I+lxO.70=1.7 3.0 4x
3.0
=0.
=1+2xO 70(1 0,573) 1+ (0.427)2 x.!. quit
1.086
19 1.0(33.30-1)1.70 +0.
nu at de hs blow counts ecorde we 18 roundwater dept of 1.30 belo ground level. Th saturate densit of 19 kN/m3. t ri p o t n g ed at de of 1. be 1.20 wide Determin th allowabl bearin Corrected value:
x~
1.08
19x3.0x48.03xO.6xl.O
1133 821.31
1954.3 kN/m
y=-
i s r eq u pressure
n; =15+t(N-15)=15+t(18-15) 16.5
3.0 51 19
nd nd he as measured at sand ha bulk
70 kN
hi ue ul ve of th foundation base i.e. 33 kN/m2.
bl
Depth correction factor: hi 3.
ve bu de
ur
19=
kN
From Fig. 4. th dept correction factor
2.50 Therefor
to
Stee beam grillage
0.10 1.22 2.65 5.39 10.88 22.40 48.03 09.41 71.76 762.89
Thic stee plate bedde
Dia gauges supported l ea r o f t h t es t a r
Fig. 4.11 Plat bearin test apparatus.
water
N'
16.50
For N' +nsity of
2.50
41 an
41
Allowable bearin pressure
49
ettlemen
test plate.
kN/m
within '1 iults of N=
.<-••
S2 th
1.20 usin Fig. 4.4:
kN/m
to
formula fo granular soils:
allow fo th groundwater levels rising.
.F .:.:nd
dete mine by carrying ou plat bearin test (Fig 4.11 However, such test must be carrie ou with full knowledg of th underlying strata as th plat il only tres li ited importan that th groundwate leve is known. Th main drawback in attemptin to determine settlements
where Q2 and QI foundation an plate, respectively an and ar thei respectiv widths Settle en prediction fr plat bearin test ar ofte cu at ck an an evelope analysis base on fiel expe ienc of al diameter plate an actua foundation an their conclusion were that, fo foundations on granular strata 0.47N
.r soil an th rd
bulk
require to re
possible an neve le than 30 he test plat houl be rigi enough to avoi bendin an ca be betwee 00 an 80 mm quar or circular he
where applie bearin pressure in kN/m count; tt es es ts it ti to an fo groundwate levels from Fig. 4.10
bearin pres ure. he loadin is then increase up to tw or thre ti es th proposed loading, an settlement readings should be recorded or each stage. here ther is no defini tive ailure poin th ulti at bearin capacity is ta en to be th tl eq al to th plat idth he result of settle en agains load inte sity houl be plotte on lo cale to determin th fail re point. Terzaghi establishe that th settlement of 30 square
in-situ ca an avel ta plac driven type precas or stee driven or continuous flight
foundation by usin th formul 2B I+B
where SI
th settle en of
foundati
idth B, where
SP blo
granular strata. In addition th risk of having poorly formed pile is rule ou when teel ection or precas conc et pile cast in factor ar used FA wher ther ar existing buil in an vibratio need to be water-bearin or very soft strata ar encountere an type of pile is needed
bore
Foundation in sand an gravel 4.7. Bearing capacity factors (after Meyerhof
Tabl
.6.1
ca en al th le tr rig. Fo large-diameter pile specia ri design is generall ci ll th le ar am to enlarg th pile base
No
Ny
(degrees)
te in at th li tr to to temporar or permanen casings. If th casing is temporar in-situ concrete system in whic th casing
5.14
1.0
10
8.34
2.50
20 25
14.83 20.71
6.40 10.70
35.47
23.20 29.40
0.0 0.1 0.40 1.10 2.90 6.80 8.0 11.20 15.70 22.0 31.10 44.40 64.0 93.60 262.30 871.70
28
in in in ev during withdrawal of th casing ar er
ck
il
it
il
ei em co te hav high workability. In extrem situations wher groundwate inflow ar high it esir th il em ip er io te ac tr ie at ld an should have
high ce en conten of at leas 40 kg/m",
bentonit slurry Th us of
tremie pipe in thes situations
tr ie to er es it whic ha to be displace by th outflowing concrete .6.2
ti
li
an
36 38 134.70
where I s
ed
to
en il af ce embedded pile length of th pile shaft. Th averag valu of Is is give by Is
In 1976
re
il
eyerho determined bearin
capacity factor fo
zantse in 1961 an by ar li te in able 4.7.
an en an Vesic, an thes factor
Ultimate load capacit Qu
Qb
where Q b lt en in co ultimat skin friction component. No qbAb
t,
a'; NqAb
where a'; th effectiv overburden pressure at th pile toe; : : th bearin capacity factor (Table 4.7) Ab area of pile at ba e. No Qs=/sA,
'v tan Ii
where K ; ; :he coefficien of lateral earth pressure; angle of friction betwee th pile haft an th surroundin oils Value fo K; and ar listed in able 4. (derived by Brom in 1966). bl
pi
ue
(Broms 1966)
s, Pil material
Steel Concrete Timber \!t'
De ig
K,
Relative densit of soil
al
been formed in uitabl bearin strata then it is nece sary to replac th auge an reform deeper pile
.6.3
; :a verag valu of skin friction develope over th
il
Thes pile ar very useful in soil such as of alluvium et an an ea ey ld en site investigatio is available. Th auge on th piling ri ha cr
32
20° 0.75 p'
0.50 1.0 1.50
Angl of shearing resistance in respec of effectiv
1.0 2.0 4.0 stress values
Th values ofIs ar limite fo pile length betwee 10and 20 time th pile diameter or pile width. Fo practica usag maximu is take as 10 kN/m2. Meyerhof determined that qb is approximatel equa to 14 where N::;: SP blow count; pile diameter or pile width; embedded length of pile in th en bearin strata Is is approximatel equa to the average uncorrecte valu over th 0.67 kN/m shaft length considered ti es av th la at il in al
ti
and im te
in
an
Therefore Ny
ca
0.0 0.1 0.40 1.10 2.90 6.80 8.0 1.1.20 [5.70 !2.0 31.10 14.40 >4.0
)3.60 262.30 °71.70
be quit
consolidatio
settlement and, belo
th
op of
it
:= angle Broms
I'
medium dens sand
1. 23.4 kN/m
Ifwe assume pile will be approximatel
ding soils.
ill,
1300kg/m an al th borehole revealed dr conditions down to 15 depth. Th densit of th sand is 1850kg/m>. it pile at 4. centres, an usin continuously designed in am xi o rk i oa on le qu 20 60 288 kN Ultimate skin friction on pile shaft, K; 'Y tano. K, and 33 an 33 24 5. he or ,= 1.0, in ic io
ic on
le oe
1.
ic on
ng th
23
1.
2.0
tan
a-
tan
cp'.
as um
be
approximatel equal. Therefor tota negative skin friction on th op 4. of th pi ha eq al 1£
0X 0= 9.
fs
kN
0.
36 kN
ed um de
29
=288+59
This is slightly less than th recommende valu of 3. bu is accept able becaus of th lo values adopte or th densit of th sands. ll
for DIB 1£X0.40
Dense
el
Therefore
4.
3 .6 4
u ri n t h b o n g h e
oi
1028 50 kN
where el effectiv vertical stress an constant fo th pile's length
+ 23 .4 9 2.0
Berezantsev chart (Fig. 4.12)
1.0 2.0 4.0
Negative skin friction
10m long
Assuming 40 mm diameter concrete piles: ki
36
pile workin load um eg iv in ct on ts ve op of he pi pe ue ga iv ki t io n i l n o ny ac over th hole length of th pile shaf embedded in th il an it i l h e e fo r b e n e to on he magnitud of th drag-dow orce to be used in th design
73.64 kN/m
ot
662.5
Adopting combined factor of sa et of 3.0, th maximu allowable workin load 1028.50/3. 34 kN us th il ti t t i n u nd e h e o w i gh t
becaus of th closenes of an ol existing building Th aximum un actore line load fo th thre storey dwelling is 60 kN pe et un o i o n i ti o lo he te on of pp xi ly
ni
.d
Ultimate resistanc
significant.
Usin 27 mm 27 mm precas concrete pile driven th ough th fill into th medium dens sand (N 25 blows) to calculated set, factor of sa et of 2.50 ca be adopted. Maximu
pile
orking load
28 2.50
6 62 .5 0 k N
300r-----~-----r-----r----~----~ 250 20
-alues
Berezantse
char (Fig 4.l2
fo a.1O
pile length
!::_ Therefore =60
10 an
Qs=lsxAs
usagefs ""';ned tha
Is
blow
where K;
I~.;d length ov
Qs
th
0= 0.75
2.0x(4.
36
27 Therefor
+6.0rz )tan27x4xo.275 2.0
2.0
~ravel th :-l'th co
and
cautious
.oose soil
tan
2~~LL~_LLi_LLl~LL~~~~LL~ Angle of shearing resistance Fig.4.12 Values of
fo pile formul (after Berezantsev, 1961).
Qb=Pb(N wher
Ab is th effectiv overburden pressure at th base of th pile
Therefore from the Berezantsev char
91
qb
V, =60 163(60 -l)X
.0
0.275
2 7k N
5x 40x35 Therefore 0.275
le
i n l oo s
Is 4. .4
s an d
05
N.
s, where
i s d is co un te d
35 kN/m2. Therefor
et calculations
Usin th modified Hile formul fo precas piles, ultimate load 867.50 kN Transfer energy at pile to 0.70 104, te po ar co pression of pile an grou er bl w, sa 12mm; se blow count. Therefore
2.50
In granular strata th en bearin componen is much greate ct en th occu at th pile toe. In dens granular trat this
s=---=---rum/blow
bearing. Applying thes factor to Exampl 4. th allowabl workin load woul be
practice.j, is take as 10 kN/m maximum.
es in
ovemen
ap
te
105
1058
70
352
capacities. qb
where SP blow count, embedded length of pile in bearin strata an diameter or idth of th pile Consider exampl 4.5:
dicted from th dynamics of th drivin operatio itself Th kineti energy imparted th pili ha er is equate to
Qb
Therefore
qb XA
25
0.275
and kN/m the averag uncorrecte valu over th embedded length of th pile in th bearin stratum. Therefor Qs
25
25
Fo qb
and
0.275
ored pile in granular soil
N e k i e ti c e n r g
to ne fallin dr heig of an causin penetratio or se of rn th pile resi tanc load R, ca be obtained from th formul R,
Wh
energy losses
14ND
Is
=0.67N kN/m2
equipment. Drivin pile into sand an gravel strata will increase th relative densit of th sand an gravel an this ha igni fican effect on th predictions of load-carrying capacity.
.6 piles
applie bu th utch formul is also ofte used he iley la ly li in thei suppor in sand an gravels, stiff-to-har clay or rock It is no applicable to frictional pile whic obtain thei suppor in soft clay by adhesion alon thei length ci li il lt
te
For
b,
400NkN/m2.
Qu
am qb
Therefor
40ND/B
or
es
er
effectiv as sophisticate
co hammer at less cost Some piling
se sands
where WH Workin pile load
actor
kineti
energy Therefor
l' RW+p
;, where
Workin load on pile 29 kN with pile length safety 2.50 Therefor 2.
95
vement
pil length;
Velocity of hammer at impact K"
menc energy
owable .6.6
or
2.62 ml
.0
mv
Reduce this valu by 30 Therefore
tv
10 x2.622
fo losses
10500. Nm
0.70
(7351)
_ W . , . ,( _ W _ H ' - ,- )
10 x37.50(30+0.648x9) er fo
ac or of
737.50 kN
Mass of hammer 3.06 kN weight of hammer, 30 kN weight of pile 0.648 kN wher effectiv hammer drop, 0.35 m.
near ay borehole locations.
9.
us thre bl ws of 50
fo
10500.
7351 Nm
8.34 mm/blow se
25
be adopted. itself Th ~-'l te
to
be used to carr
safe workin load of 350-50 kN Th pile is reinforced with eigh 12 high ns le rs in ir un le r. on rete Fy 59 N/mm2; Feu 50; A's 452;
ground. 4.6.
I~
ase-driven stee tu
Ultimate axial compression load:
s+ 12.70
where Ru
ulti
0.40 e u A e riving resist nc
nnes
weight
form
is
plic bl
or
Ru
m.
4.6.
Top-driven stee
ck.
is
su port in
iles
make
r;
452 590 191 kN
10.
ff
iv
ha
drop
tres
2.25
in newtons;
lows
fo
0% loss
ff ie y:
2.25
787.50 kN
of pile an ground
ha it
8500 0x2
newtons; Allowi
350
with factor of safety
0.85 10m
104k m; temporar Se pe lo inmm S,
5.8 mm/blow
where
'.yle drop
piling
00 20
metre penetratio per blo
RW+p
length :0
s+c/2
compressio is give by
he Hile ti thei
1512 50
0.75 As
Fo workin load of 35 kN usin modified Hile formul
crease th ;1< signi.ity.
=452.
290W(1.0+h)
~h of resistance
compre-
pi es
00
er iv se ther fore us .0 banut rop. or workin lo of 350- 00 N:
.!.Q.
2.6 mm/blow
refore blow ha .0 banu ha er wi 00
give 26 ro se
et he fo bl .9
se
Foundation in sand an gravel le 4. type)
(Rig: hydraulic Banut
Hammer weigh (tonnes)
Hammer drop (mm)
capacity of piles:
OA
1.05
D UT C
AO
F OR M UL A
This ormula provides an alternativ se usin dynami formula. s=
Berezantsev,V.O. (1961) Loa bearing capacit and deformatio of pile foundations Proc Fift nternational Conference on Soil Mechanics, Paris, ol 2, pp 11-12.
Transfe energ (tonn metres
1.50 3.00 4.00 5.0
method of determinin
W2KH Ru(W+
where se in mm/blow weigh of hammer 35 kN hammer efficiency 0.70; hamme drop 450 mm; Ru
weight of pile Therefore
3500(35+18)
18 kN
2.27 rnm/blo
Fo te blow this equals 22.7 mm set.
BIBLIOGRAPHY
pile
summary. Sols (Soils) 5(18/19) 21-31.
foundations, British Standards Institution Carter M. 1983 Geotechnical Engineering Handbook Pentech Press, London. Beer E . E . 1965 Bearin capacity an settlement of shallo foundation on sand Proc Symposiu on Bearin Capacity an Settlement of Foundations, Duke University pp. 15-33. i bb s ol 9 57 ) R e ch te in ng he Proc Fourth ICSMFE Conference, London Vol. pp. 35-39. Meyerhof, 0.0. foundations. Geotechnique, ( 4) , 301-332. Pa ry R. .O (1971) direct method of estimating settlement in sand from SP values Midlands SMFE Society. Powell M.J.V. (1979) House-Builder's Referenc Book, NewnesButterworth, London. Terzaghi, K. an Peck R.B. (1968) Soi Mechanic in Engineering Practice, 2n edn, John Wiley, ew York Vesic, A.S. (1966) Test on instrumented piles. Ogeechee Rive site. American Society of Civil Engineers,
Chapter
111dtion of
Bui localities
:' on Soil iearing -;:d.
ictice fo
mi ng
)f shallow
;'ityand
c.
Fourth of
lements
in
igineering River
Th followin guidance is give fo builders an engineer in lv it an ng an co ru ti ou te pr io er in er extr tion te ut ex ra ti co er in al ll take plac afte th developmen ha been completed.
Division,
shafts adit etc. an variou foundation design option ar availabl to cate fo an ground ovements likely to arise. de ce th th er ls ch ecla sandston (EIlan flags) chalk, ironstone, salt an gypsum ic an bili pr em el e. he ef ct bsid nc od lo al ex ra ti th accurately wherea
ovements resultin
from ol shallo
soun judgements by engineer an geologists experience
Coal, lead, tin, ironstone, fireclay sandstone, gypsum salt, tr cted io ho er he ar th industries relate to th minerals have gone into decline. At gypsum anhydrit an salt an yd te in ar ex en el ed in Cumbria, orkshire Nottingham hire an Sussex bu th nature of th workings result in very larg pillar bein left pr de up er in tr ta ea ex 0m thic beds of material 30 Chal wa mined in similar fashion using pillar-and-stal ch ea th ve ly tr ta collapse into wallow hole in th chal an this material is usuall mass of loos voided aterial. In area of wallow acti it li ta en elow th ha is generally ir d, if le ar la an de ea th
data collected. often unpredictable subsidence shallo
coal workings or othe minera workings ca result
difficul to quantify prio to consolidatio bein carrie ou becaus of th lack of informatio on th volume of material
over th no-build zone
If hallow
render
effect in pu hing mine ga es such as site undevelopable.
pumpin an th de ig of foundation in such area requir special considerations.
orking ar discovered
properties availabl to spread th costs. In know mining area it is pruden to consul Britis Coal th bo es th in ar er va ue an Britis Geological urvey, before purchasing an land fo development In some localities planning authorities ma la down conditions in regard to ol or future minera extrac
diaphrag
the site infrastructure
ethane an
Originally used as mean of obtainin fireclay or ironstone, bell pits (Fig 5.1) were in us from th thirteenth centur up he ea ly os er al nd in ar as th thicknes of drif (superficial deposits wa relatively thin thes pits rarely exceeded 12m
ld en ou er
he consiste of
vertical
nd ir on an hi as te eti ts ca ated in ai an interconnected at th bottom To facilitate ventilatio fire
