IR(:
37-1984
GUIDELINES FOR THE DESIGN OF
FLEXIBLE PAVEMENTS (Pirsi Rcvlsion)
THE TH E INDIAN ROADS CONGRESS 1995
lkC: 37-19fl4
GUIDELINES FO THE E DESIGN FOR R TH OF FLEXIBLE PAVEMENTS (First Revision)
Published by
THE IN THE INDI DIAN AN RO ROAD ADS S CONGRESS ~Jamnag ~Jam nagar arHous House, e, Sh Shahja ahjahan han Road, N e w Delhi — 110011 1995
<<
Price Rs, 100/ / Plus Packing & Posta~e)
First published Reprinted First Revision Reprinted Reprinted Reprinted
September. 1970
December. 1 9 7 6 Decembet 1984 October 9 9 0 (Incorporates A m e n d m e n t N o 1 . Se ptem be r 1 9 8 8 ) :April, 1995 October, 2000
( R (g( g h & c of Publication a n d of Thansiwion a r e R es en ia(1
Printed a t D e e K a y Printers, New Delhi (1000 copies) <<
CONTENTS
Introduction 2.Scope 3 . Recommended M e t h o d o f Design 4 . Thickness a n d Composition S . Drainage M ea su res 6 . D es ign in Frost~AffectedAreas 7 . Worked Examples Illustrating the Design M e t h o d Appendices .lppcndix 1: Preparation of Laboratoiy T e s t Sp ecim en s Ippendix 2: Special Points Relating t o D es ign o f Pavements on Expansive Soils 1.
2 3 15
22 25 25 29
•
<<
31
IRC: 37-1984
GUIDELINES FO R THE DESIGN OF FLEXIBLE PAVEMENTS 1. INTRODUCTION
Thee design of a flexible pavement involves th e interplay of several 1.1. Th con nvariables such a s t h e wheel loads, traffic, climate, terrain and subgrade co ditions. In t h e existing state of knowledge, the individual effect of many of these factors is difficult t o evaluate mathematically with any precision. Hence, a fully acc acceptabl eptable, e, theoretical method of design has not emerged as yet, and the methods i n vogue have of necessity to be empirical, based on successful past practices and experiences, and some quantitative evaluation of th e subgrade soils, t o yield designs capable of withstanding given conditions of traffic and climate. diversee practices practices hav havee been prevalent i n regard to the 1.2. In India quite divers provision of pavement thicknt~ssesso far. Considering the need ~o have a unified and reasonably acceptable approach for working out the c~i~n for for conditions obtaining in th thee cou country ntry,, th thee Indian Roads Congress, through ititss Flexible Pavement Design Subcommittee (personnel given below), set up under the Specifications and Standards Committee examined the various possible methods and formulated guidelines for general adoption: SN. Sirtha
Convenor
R.P. Sikka B.R. Chopra
Member-Secretary Member
Dr. C.E.O. Justo
D.R. Kohli Mahalir Prasad J.S. Marya
N.Sen Dr. Bh. Subbaraju
Prof. C.G. Swaminathan D r. H.L. Uppal
1.3. These guidelines were approved by t he Specifications and Stan-
dards Committee i n their meeting held on t he 26th and 27th February, 1970 and by the Executive Committee in their meeting held on t he 5t 5thh March, 1970 and later b y the Council in their meeting held a t Darjeeing on t he 5t 5th h and 6t 6thh April, 1970.
A subgrouppersonnel given below wa wass constituted in 1984 to review <<
I
JRC :37.1984
t h e guidelines in light of need t o meet the heavier axle loads and keeping i n view the suggestion made i n the Panel Discussion during t h e Annual Session of t h e Indian Roads Congress held at Nagpur i n January 1984. K.K.Sarin
Convenor
N. Sivaguru
Member-Secretary
Dr . M.P. Dhir
Member
SB. Kulkami Dr.C.E.G.Justo
N.Sen P.K, Lauria S.A.LaLheef
S.C. Shaima
Th e guidelines as revised by the subgroup were approved by the The Executive Committee and later by t h e Council i n their 111th meeting held at Tnvandrum on the 15th September 1984. 1.4. It i s emphasised that the guidelines are t o be regarded as tentative ~.syet, to th thee ext extent ent th that at th they ey would require revision from time t o time i n th e light of future experience a n d developments i n this field. Towards this end, usee t h e guidelines for it i s suggested t o a ll the organisations intending t o us strengthening of existing pavements or the design of pavements of new roads t o keep a detailed tabulated record of the total thickness, type of construction, construction, period betw between een renew renewal al coa coats ts and the year t o year performance of the individual sections of pavements. 2. SCOPE
2.1. For the purpose of this guide, flexible pavements are considered t o include the usual granular type constructions such as water bound macadam and other flexible bases andsub-bases conforming t o IRC Standards or t o Sections 40 4000 and 50 5000 of the Ministry of Surface Transport Specifications for Road and Bridge Works (Second Revision), 1988. 2.2. The recommendations primariiy apply to new constructions. However, for the time being these guidelines will also apply t o design of strengthening measures for existing pavements until a more scientific approach t o overlay design i s developed for Indian conditions. Special points relevant to strengthening of existing roads are highlighted where necessary. <<
IRC :37-1984
alternative approach to overlay design is de desc scri ribe bed d in IRC: 81-1981 ntativc Guidelines for Strengthening of Flexible Road Pavements using enl~elmanBeam Deflection Technique”.
n
3. RECOMMENDED METhOD OF DKSICN
3.1. General
Thee method of design recommended i s a modification of the I. Th Thhfornia Bearing Ratio (CBR) Method indicated i n the previous edition. In i s method traffic i s defined in terms of the cumulative number of standard xles (816() kg) to be carried during t h e design life of the~road. it i s well ecognised that t h e structuraldamage caused by a vehicledepends on th thee ax axle le oad it imposes on the~road, and th e equivalent axle load concept is t h e best ethod available, for design purposes, to handle the large spectnim of axle oads actually applied t o a pavement. Th Thee design curves relating pavement hickness t o th e cumulative number of sta stand ndard ard axles t o be carried for Thee subgrade strength iifcrcnt iifcrc nt sub-gr sub-grade ade strength values are given in Fig. 1. Th s assessed in ter ms of the CBR value of th e subgrade soil as per procedure escribed in paragraph 3.3. Th Thee thicknesses deduced from Fig. I are total hicknesses and consists of various combinationsof bitum bituminous inous surfacing and ranular base and sub-base thicknesses. The recommended minimum thick esses and compositions of com compon ponent ent lay layers ers for new con constr struct uction ionss are given n Thickness Thickness Combination Combination Block Block,, Fig.2 Fig.2.. These may,however, be modified if nviron nvi ronmen mental tal con condit dition ionss and experience so justify. In cases of traffic stimates exceeding 30 million standardaxle (msa) the curves may be suita suita-ly extrapolated liar determining the design thickness. 3.1 .
recommende mended d metho method, d, where 3.1.2. Notwithstanding the aforesaid recom ata is riot available to adopt the equivalent axle load concept, the CBR wthod which considers traffic in terms of commercial vehicles per day may e used provided the design traffic isnot more than 1500 commercial vehicles er day. The CBR curves updated for 10.2 tonnes single axle legal limit resently in force arc recommended for design, Fig. 3. Estimation of the esign traffic is described in paragraphs 3.2.1., 3.2.2. and 3.2.4., and th e rocedure br determining the CBR value of the subgradc soil is described in aragraph 3.3. The thickness of di diff ffer eren entt la laye yers rs of su subb-ba base se,, ba base se and urfacing can be determined by repeated use of these curves and duly taking to account the minimum thickness and compositional requirements speciied in pa para ragr grap aph h 4. As the requirements with regard to the minimum <<
IRC
:37-1984
‘Is I-
‘Is
I -J ~1 I 45~
m
z
r
U
I-
I-.
z ‘I S
I 115
>
-i
50 5-
0
Os
02
44 06085 CUUULATIVt
2 STANDARD
4
4
8 10
3015 1506 06 5 5 20 30
AXt.tS
Fig. 1 . Pavement thickjiess design chart N o s e : 1 . R e a d total p a v e m e n t thickness from cOnhilMIouS c u r v e s forr proportioning s u b - b a s e thickness 2 . U s e dotted curves fo
<<
4
IRC: 37-1984 THS HSCSCNES ESS
COM8~NATION
~
BINOU OUS SI’-
—j4
SURPACING 3RANULAR
TOTAL Th$CXNESS
‘V FROM THICKNtSS CIIAR’T
‘~
BASE
et~OCK
-it~~~ -
GRANULAR SUB Bs*5t
m~.t. ~ m~
Fig. 2 STRUCTURAL SECTION
Minintwn thickness of compo~tent layers compo~tent
Cumuld ted standard
shickjiess (mm) compacted shickjiess compacted
axles ,ndleopi (Id)
Base (Y)
Surfacing (X)
L).5 M
20mm PCj2-Coat SD
150
Subbase (Z)
(T--150) Minimum thickness 100mm o n subgrades of CBR less than 2 0% (T-.225)
052M
2OmmPC/MS
225
I
Minimumthickness 150mmo~s sobgrades of CBR lesa than 20% ~T--3OW325) Minim~thickness 150 mm on subgrsdes of CRR less than 30~
2-SM
20mm1~1MS/SDC + 50 mm TlS m m BM
250
5-10 N i
25mm SDC/AC #bOtoSOmmDBM
250
10-IS Ni
40mm S DC/AC 4 65 to 80 m m DBM
250
(1~--355 to to 370) --do--
15-21) Ni
4OmrnAC
250
(T--370 to 390)
+
20-30 Ni
SD PC MS
SD C AC H 51 DIIM ~oie : <<
1
S0t~100mm
+
--do--
DBM
40mm AC itS S rum DOM 0010 it
(T-335 so 355)
--do.-
250
(‘7-390 to 405) -
-
do..
-Surface dressing to the MOST Specification IRC/Standards Premix Carpet -doMix Seat Surfacing to thc MOST Specification Se m i-i -d e n s e Ca r p e t -doAsphalsic Concrete -doBituminous Macadam Binder Course to the MOST Specification Dense Bituminous Macadam Binder c:ow-se (i) If the C BR of the suhgrade is more than the minimum requirement for the subbase, rio subbase is required. (ii) Binder course of thickncss more than 80 mm should b e laid in tw twoo ayers.
IRC :371984
CALIFORNIA
3
SEAR~SO
RATIOS
PERCCNT
4
E
2
z x
U S fr 2
0 U
2 0
lL~ lL ~ 0
2
a
w
0
Fig. 3~CBR. cunes for flexible pavement design
<<
IRC :37-1984
ickness and composition of various layers specified in paragraph 4 are in rms of cumulative number of standard axles,, the following approximate affic conversions may be used to decide the minimum thickness and co com mosition of various Layers:
Traffic range
( i1 (ii)
D e s ig ign irsific uplo 1 50 cs/day (CBR curve ABC) Design traffic iSO 450 cv/d~ iCli K curve 0) FOsig,n traffic 4511-1500 cs/day CO R curve El
Adopt minimum layer thicknes thicknes s a n d composition applicable to Upto 0.5 nssltion standard axles (tnsa) 1)-S to 2 m s a ‘2 to 4 m s a
Traffic 12.1. General
1,2.1] - Feim the. pu purp rpos osee of st stru ruct ctur ural al de desi sign gn only the number of anti th their eir axleommerc omm ercial ial veh vehicl icles es of lad laden en weight of 13 tonnes a’ more anti oading will be considered. 1.2. To obtain a realistic. estimate of desi,grt traffic due considera— on should he given to theexisting traffic or that anticipated in thecase of new .tynstru~c:lions,[X)ssiHechanges in road network and land use. of the area erve.d the probable growth of traffic, anti design life.
Estimate of the inItial daily average traffic flow for any road s:hould ormally he based on 7-day 2,4-hour classified traffic counts. However, in .xcepliooal cases where this information is not available 3-day count could e used. In cases of new roads traffic estimates can be made on the basis of
otential land use and traffic on existing rotites in t h e area. An estimate of li like kely ly gro growt wth h ra rate teca can n be obtained by studying the past rends in traffic growth. If adequate data is not available, it is recommended If adequate hatt an average value of 7.5 per cent may be adopted for ruial routes. ha <<
ERC :37-1984
3.2.2. Design life
3.2.2.1. Itis considered appropriate that roads in rural areas should b e designed for a life of 10-15 years but provision must be made i n th thee des desig igii fo forr progressive strengthening of the road. Arteria Arteriall roa roads ds should normally be designed for 15 years life and others fo forr 10 years life. Urban roads may, however, be designed fo forr a longer life based on judgememu arid depending on t h e iate of growth of the traffic expected. 3.2.7.2. Very olten it may n ot be possible t o provide the full thickness of pavement needed ultimately right a t t he time of initial construction. Stage construction techniques should be resorted to in such cases and those forms of construction chosen that could readily be ~t.rengthenedas traffic increased. The initial stage period should n o t b e less than 5 years. forr use of pavement thickness 3.2,3. Computation of traffic fo design chart given in Fig. 1 . 3.2.3.1. The design traffi trafficc is considered considered in terms of the cumulative number of standard axles (in t he lane carrying maximum traffic) to be carried during t he design life of the road. Its computation in invo volves lves esti estimat mates es of the initial volume of commercial vehicles per day, lateral distribution of traffic, the growt dam mag agee facto factorr (number growth h rate, the design life i n years an and d th thee vehicle da of standard axle pe perr commercial vehicle) t o convert commercial vehicles t o
standard axles. may y be used to make t he required calculation: Thee following equation ma Th N~=
where
<<
F
r N~=The cumulative number of standard axles to b e catered forr in the design fo A= Initial traffic, in th thee year of completion of construction, in terms of the number of commercial vehicles per day duty modified to account for lane distribution as explained in paragraph 3.2.3.2. r= Ann nnu ua l growth rate of commercial traffic x= Design life i n years F= Vehicle damage factor (number of standard axles per commercial vehicle) refer to paragraph 3.2.3.3.
IRC
:
37-1984
3.2.3.2.. Distribution of commercial traffic over the carriageway: A and d by of commercial commercial traffi alistic assess alistic assessment ment of distribution of trafficc by directi direction on an ne is nec necess essary ary as it dir direct ectly ly aff affect ectss t he total equiva equivalent lent standard axle load pplications used in the design. In the absence of adequate and conclusive forr t he time being t he fol ata for Indian condit conditions, ions, it is is recom recommende mended d that fo fol-wing distribution may be assumed for design until more reliable data on lacement of commercial vehicles on t h e carriageway lanes are available: (i) 5ingle~laneroads (3.75 its width): Traffic tends to be more channelited o n single lane roads than o n two lane roads an and d to design gn shou should ld b e based on the allow for this concentration of wheel load repetitions the desi total number of commercial vehicles per day in bosh directions multiplied by two, (ii) Intermediate width roads (5.5 m width): commercia erciall vehic vehicles les per day in both ‘i’hc dcsign should he based on the total number of f comm direction dire ctionss multi multiplied plied by 1.5 (iii) Two~lanesingle cas-rtageway roads:
mc design should bebased on 75 per cent of the total numb number er of commerci commercial al vehic vehicles les in f the both directions, (iv) Four~lanesIngle carr carriageway iageway roa roads: ds:
The des design ign should be ba base sed d on 40 per cent of she number of comm commercia erciall vehicles vehicles in she soul number both directions. (v) t)ual carriageway roads:
The des design ign of dual two-lane carriageway roads should be basedon 75 per cent of the f dual f the number of commercial commercial vehicles in each direction. The distri distributi bution onfactor shall be reduced by 20 per cent for each additional lane, Er
For dual three.lane carriageway distribution factor-60 per cent.
The tra traffi fficc in each dir direct ection ion may may be assum assumed ed to be hatf hatf the sum in both directions when the laster only is known. Where significant difference between the two streams trafficked icked lane should be considered for can occur, the condition in the more beavily traff design.
However, if i n a particular situation a better estimate of the dis distrib tribut ution ion traffic between the carriageway lanes is available from traffic surveys, the me should be adopted a n d the design i s based on the traffic i n the most avily trafficked lane. The design will normally be applied over the whole rriageway width, <<
9
IRC :37.1984
3.2.3.3. Vehicle damage factor: The vehicle damage factor is a multiplier fo thee number of commercial vehicles of different axle loads forr converting th dam m age factor is to Ihe number of standard axle-load repetitions. The vehicle da arrived at from axle-load surveys on typical ro road ad sec secti tion onss so as t o cOver various influencing factors such a s : traffic mix, type oftransportalion,type of commodities carried, time of the year, terrain, road condition and degree of may y be us enforcement. Th Thee AASFIO axle-load equi equival valence ence factors ma used ed t o convert t h e axle lo:J spectrum toan equivalent number of standard axles. For designing a new rojiL~pavement or strengthening an existing road pavement, t h e vehicle damage factor ~hutsklbe arrived at carefully by using c’ relevant available data. Some surveys ha\ been carried out i n the country on National cann be taken advantage of, t o the extent that Highway sections, Th Thee results ca they may be relevant i n a particular case. TABLE TAB LE I. iNDICATIVE VDF VALUF.S
Initial traffic intensisS’ in tenns of situnber
Terrain
of eontine rcial vehicles/day
1500 Less than 15
VDFvaluea (standard axles of 8.16) tonnrs per commercial vehicle)
f
Hilly RoIling Plain
Unsurfaced
Thin bituminous surfacing
Thick bituminous surfacing
0.75 1.75
0.5 1.5 2.0
2.25
5000 150.1 50
Hilly RoIling Plain
1.0 2.0 2.5
1.25 2.25 2.75
More than t5(X)
Hilly RoIling Plain
1.25 2.25
1.5 2.5 3.0
2.75
Where sufficient inform Where informati ation on is n ot available, the tentative indicative values of vehicle damage factor a s given in Table 1 ma may y be used. These may be judiciously modifie.d for any special conditions with regard to tra ff ffic ic mix, type of transportation, etc. The validity of t h e value chosen ma may y be checked after the pavement has been put to use, so that the warranted corrective steps can be und undett ettake aken. n. <<
10
tRC : 37-1954
traf affi ficc fo forr use of CRR design curves :3,2,4 . Computation of tr given in Fig. 3 3.2.4.1. The CBR curves (Fig. 3) give t h e total thickness of t h e
paveme pave ment nt in te term rmss of th e volume of com commerci mercial al traffic. The traf trafffic i s considered i n units of commercial vehicles perday i n both directions divided usee categ~arie~s a s indicated in Table~2. tnto t us
TI0 N OF TR A FF tC TAstui 2 , O .A 5SI F 1FA TI0
CBR design curve applicable
Trslfic cOlTllsscrcIsl
FOR D E S IG N
vehicles Ix:r dat)
0.15 15-45 45-150
A
150450
1) 0
B C
450-15(X)
The. design curves are t o be used with respect t o th e number of corn corn-Thee formula for predicting mcrcial vehicles exp expect ected ed at th e end of design life. Th future fu ture tra traff ffic ic is given by: A Where perr day fo forr design A = Number of commercial vehicles pe P Number of commercial vehicles pe perr day at lass count f commercial Annual gro growth wth rat ratee of com commer mercia ciall tratlic n r. Nusnber of ycass bet betwee ween n the last count and the year of completion of consitu ction =
=
a
Design Des ign lif lifee is s years
o-lane ne roads t h e design will be based on the number of 3.2.4 .2.. For U h v o-la commercial vehicles per !~avi n both direct directions ions where whereas as single lane roads should be designed
for
twtce the traffic in both directions.
3.2.5. Where traffic is increasing rapidly, it is probable that a singlelane~road may require upgrading t o two-lane standards within a short period even oth otherwis erwisee and thi thiss aspect aspect should be borne i n mind when deciding t h e pavement thickness.
3.3. Subgrade 3.3.1. The subgrade whether i n cut or fill should be well compacted t o overalll Ihi Ihickn ckness ess of utilise ititss full strength and t o economise thereby on the overal pavemenl required. Most specifications prescribe us usee of selected material and <<
11
IR C
:37.1954
stiffer standards of colnpaction in lh lhee to top p 50 cm portion of the roadway (usually 9 5-1(X ) per cent of lhe Stand Standard ard Proct Proctor or density; somet sometimes imes even even
higher) and these clauses should h e strictly enforced. IRC.’36-1970 “Recommended Practice for t h e Construction of Earth EmhankmenLs for Road Works’’ should be followed for guidance.
3.3.2. For design, th thee sub subgra grade de strength i s assessed in terms of t h e CB CBR R of the suhgrade soil at the most crittcal moisture condition!’s likely to occur insitu.
3.3.3 . Since 3.3.3. Since th thee OR test is an a d hoc penetration test, it i s necessary procedure re should be strictly adhered t o .... This is dethat the standard test procedu scribed i n 15:2720 (Part XVI) “Methods of Test for Soils : Laboratory Determination of CBR”. The test must alway alwayss be performed on remoulded samples of soils in t h e laboratory. Wherever possible, t h e test specimens should h e prepared by static compaction but if n ot so possi possible ble dy dyna nami micc may y be used a s an al rne:hod ma altern ternat ative ive.. Bo Both th proc procedu edures res are described i n brief in Appendix 1 . In-situ tests are not recommended for design pu purp rpos oses es as it i s n ot possible t o satisfactorily simulate t h e critical conditions of dr dryy density and moisture content i n the field,
.3.4.. Selection of d r y density and moisture content fo forr test spedmen: For a given soil, th e CB CBR R va value, lue, and consequently the design, will depend largely on the density and moisture content of t h e test sample. Therefore, the test conditions should reproduce as closely as possible the 3
weakest conditions likely to occur under the road after construction.
3.3.4.1. For new roads, the samples of soil should be compacted t o a dryy density corresponding t o t h e minimum state of compaction likely to b e . dr achieved in pract practice ice havin having g regard to the compaction compaction equipm equipment ent used and the
compaction limits specified. By and large Proctor density (conforming t o IS:2720 (Part VIl)) could be made use of. In th e case of existing roads, however, t h e moulding density should correspond t o t h e actual density of the suhgradc soil as determined in-situ with the help of a sand-jar apparatus ‘ n accordance with procedure laid down in IS : 2720 (Part X.XVIIi). 3.3.4.2. The choice of moistu moisture re con conten tentt of the tes testt spec specime imen n isn o t quite Thee moisture condition of the suhgrade which the test sample is so simple. Th
expected t o simulate i s governed by local environmental factors such as the water table, precipitation, soil permeability, drainage conditions and water<<
12
IRC: 37.1984
roofness of the pavement The surfacings provided in India are relatively in and permeable which do n ot always seal the pavenient effectively against gress of water. Further, t h e berms and verges are tsually unsurfaced, and ot kept in well-maintai well-maintained ned state state to the requis requisite, ite,crosscross-fail, fail, which which enabl enables es the rface wa water ter to rea readil dily y percolate into the subgrade from near the edges edges of the
avement, leading t o weak subgrade conditions. I-fence, it is recommended that as a general practice the design for new
nstructio nstru ctions ns sho should uld be based on t h e strength of t h e samples prepared at ptimum moi moistu sture re con conten tentt and dry density corresponding toProctor compacforr a period of four days prior to testing. If the o n and soaked in water fo ubgrade soil is identified as expansive soil t h e moulding density and moisre content should be as discussed i n Appendix 2 . casse of existing roads requiring stren I n th shou ould ld be thee ca strength gthening ening th thee soil sh oulded at the field moisture content and field density and soaked for four forr moulding should b e ays prior to testing. The field moistu oisture re co nten t used fo etermined preferably immediately after the rainy season. However, i n case is not found practicable to determine the field moisture content i n t h e right eason, or there i s difficulty in moulding the samples at this moisture content, pecimens for test ma may y be prepared simply at optimum moisture content; e s e must of course b e . soaked prior t o testing.
I t is recommended that measurements of field density a n d moisture strengthening ening of existing roads should be ontent, in t h e case of designs for strength be,, farr a s possible, carried out at a distance of 0.6 t o 1 m from the pavement s fa dgee be dg belo low w th thee pavement.
soak aking ing for four days may 3,3,4,3, However, it should be realised that so e an unrealistically severe moisture condition in certain cases. Cases falling this category would be be:: (i) Subgrades (excluding espansive soils) of roads where a comparatively thick bitumiimpernseable** nature is provided on top, such as a well laid and nous turfacing of f impernseable** sealed seale d dense carpe carpet, t, and where simultaneously (a) water table table is too deep to affect the subgrade adve adversely rsely (i.e. greaterthaa t m in sandt and 3m in sandy clayt), and (b) well<< shaped verges exitt facilitatingquick drainage of the surface water to the the sid sidee dra drains ins and(or pavement base layer is continued across pan/full width of the verge with the same objective.
their thickness, bitsiminout constructions su **trrespective of their such ch as open graded premix, ituminous mac perr rent, are no nott macada adam, m, or gro groute uted d mac macada adam, m, hav having ing voids content of more than 5 pe f more b. deemed as impermeable.
13
mc
:37~19S4 (ii) Subgrade in areas (esclssdirsg expanssve soil areas) wher wheree the clima climate te s arid through year, i.e i.e., ., the annual tsissfaii is of th thee or orde derr ofSO ofSO cm csr less and the water water table out the year, rs too deep to affect the subgradc adversely.
In th e above. .situations it is anticipated that the. most severe moisture c,:onditon in the field will he far behind that of the sample at the end of four d.ays soaking, resulting, in unduly c.onservative designs if soaking procedure was adopteti Hence the procedure of s.oaking for four days could be discarded in such cases an and d th thee sp spec ecim imen enss tested immediately after compa compaction ction a t moisture contents indicated i n the next paragraph. 13.4.4. It is recommended that fbr the determination of CBR the soil specimens of category (i) road should he compacted at optimum moisture Proctor or cotnpa cotnpaction ction test. Investigati.oi.s have revealed that content in the Proct under t h e circumstances . of thes.e roads the most adverse moisture condition of t.he subgra.de soon after withdrawal of the monsoon is in genemi drier than the optimum moisture content. In a.rid regions the normal road camber and any y exc excess essive ive surface. wate.r drait age measures will usually sufflce t o prevent an accumulation of water beneath the pavement. Therefore, it is recommended be.. prepared a t natural that soil specimens for category (ii) roads should be moisture content of the soil immediately after recession of the monsoon at suhgrade depth for finding t h e CBR value,
3.3.5. l.Jse of test results for design and the minimum number of tests required 33.5.1. Th Thee design should h e . base.d on the CBR value of th e weakest be.. encounlere.d extensively a t subgrade level over a soil type expected to be given section of t h e road, a s revealed by the soil surveys. Pavement thickness may ma y be modified a t intervals on new roads a s dictated by the soil changes but generally it will be found inexpedient to doso more frequently than once or twice per kilometre. Frequent changes in crust thickness are, a.t any rate, an undesirable feature on resurfacing prqjeccs because of their possible adverse
effect on th e longitudinal profile of the road. Hence, these should be resorted t o only when very necessary in the interest of structural design.
con n3.3.5.2. it i s possible that in certain soil types or under abnormal co ditions the measured CBR. values may appear doubtf doubtful ul and n ot truly representative of t h e stre.ngth of soil. A more complete study of the soil may be warranted i n such cases t o arrive at a more reliable design. <<
tRC 37-1984
3.3.53. On new works thc. design evolved shotilil be revised at site if fotind necessary during t h e construction phase on account cd’ th thee fiel ieldd compaction beinglower than that anticipated. Normally this could h e got over by increasing t h e thickness of the. sub-base. in addition, there should also be provision for t h e removal of local areas of soft soil.
Thee reproducibility of t h e CBR results is dependent on a 3.3.5.4. Th number of factors a n d wide variations in values can be expected. Therefore, i n order t o avoid errors, at least three samples should be lesied on each type of soil at t h e same density and moisture content. This will enable a reliable average value t o be obtained i n most cases. To weed out erratic results, iermissihle maximum variation within the ClIP values from three specimens i s indicated below: cent) Cfl (per (per cent)
~
Upto 10 Above 10 to 30 Above 30 to 60 Above 60
3 5 10 Not significant
Where variation is more than the above, t h e design CBR should be the average, of test results fro m at least s ix samples a n d n ot three. 4. TFt1CKNESS AND COMPOSITtON
or Fig. 3 i s t h e total physical thickness t o be provided and consists of granular sub-base, granular base and cann lx~dctived from bituminous surfacing. A practical design of this thickness ca t h e thickness Combination Block given in Fig. 2 which specifies t h e minimum thickness of individual pavement layers in terms of t h e cumulative stand ndard ard axles to be carried. Examples illustrating th e design number of sta The thickness deduced from Fig.
1
method a r e given in paragraph 7. In stage constr construction uction,, the thickness of sub-base should be provided to ultimate pavement section for th e full design life and t h e thickness of road Thee sub-base and base base should be based on t h e initial stage period chosen. Th bitum uminou inouss surfaci surfacing ng (20 mm premix.. a r e placed and covered with a thin bit carpet) without a n y underlying layer of bituminou.s hinder course. Extra pavement thickness is added when th e first stage design traffic h a s been c.arried. Example 2 given i n paragraph 7 illustrates t h e design procedure for <<
stage construction.
:37.1984
4.!. Sub-base Sub-base -base ma materials terials comprise natural sand, moorum, gravel, 4.1.1. Sub erite, kankar, brick metal, crushed stone, crushed slag o r combinations reof or a n y other material like stabilised soil whichremains stable under urated conditions. Ministry of Surface Transport Specifications fo forr 401)) rec recom omm mend th three ree gradings and nular sub-base materials (Clause 401 cify that the materials passin g 425 425 micron siev sievee wh when en tested i n accordance should uld ha have ve liquid limit and plasticity index of n ot more th 15:2720 (Pail V) sho n 25 and 6 respectively. These requirements should be enforced. sub-base se ma material terial should have minimum CBR of 20 per cent for Thee sub-ba Th forr ulative traffic upto 2 million standard axles (msa) and 30 per cent fo ficc exceeding 2 msa, However, where t h e sub-base required is 300 mm fi may y be substituted i n the lower portion by mateck or more apart of this ma l with a minimum CB perr cent subject to a minimum layer thickness CBR R of 10 pe 150 mm of either material,
For very l ow trafficked rural roads th thee CB CBR R requirement may be axed t o 15 per cent.
Thee material should be tested at the dry density and moisture content Th ected i n th thee fiel field. d. Where soaking co cond ndit itio ions ns appl apply y for design, the sub-bas -basee ma material terial should be determ nimum strength of the sub determined ined after king the test specimen i n water for four days. Where t h e proposed sub-base terial contains an appreciable amount of particles coarser than 20 mm, ititss cann be es ti.m ti.mate ate d from past experience or by conducting t h e CB tability ca CBR R t on th e fraction of mat ateria eriall passing 20mm sieve i n accordance with Clause 1.2.2. of the MOST Specification. ofaa sub-base is found necessary, the thickness provisi ision on of 4.1.2. Where prov forr cumulative traffic upto 0.5 ms uld n o t b e less than 100 mm fo msaa a n d 1 5 0 forr traffic exceeding 0.5 m sa fo
perr cent a capping 4.1.3. Where t h e CB CBR R of t h e subgrade i s less than 2 pe e r of 1 5 0 mm thickness of material with a minimum CBR of 10 p e r cent o be provided i n addition t o t h e sub sub-bas -basee requi required red for CB CBR R of 2 per cent. 4.1.4. If the CBR of the subgrade i s more than th thee minimum require-
n t for the sub-base., n o sub-base i s required. <<
tRC: 37-1984
4,1,5, In areas affected by frost, care should be taken to avoid using frost susceptible materials i n the sub-base,
4.2.. Base
4.2.1. Thicknesses deduced from the design cha charts rts are are appropria appropriate te t o avenlents with unbound granular bases which comprise conventional water .eund macadam, wet mix macadam and a n y other equivalent granular :onstruction. 4.2.2. Base materials must b e of good quality so as to withstand high stress concentrations which develop immediately under th thee wearing surface. For this reason it i s recommended that normally no material with CI3R value less than 100 pe perr cent should be used i n base construction. Since b a ses wi will ll b e affected by water their strength should be determined on soaked specimens. of particles particles Where a substantial part of t h e proposed base material consists of larger than 20 mm size, the CBR test will n o t be applicable and their strength wifl have to be estimated from experience. Standard conventional constructions of adequate thickness over a properly designed sub-base will be assumed to satisfy the CBR requirements of 100 p e r cent.
Thee recommended minimum thickness of granular road-base in 4.2.3. Th terms of cumula cumulative tive numbers of standard axle to b e carried is given in Fig. 2. A minimum of 15 cm thick mad-base i s considered necessary even for lightly trafficked roads. 4.2,4. When a bitumen bound structural layer is provided in addition t o the minimum bituminous surfacings specified i n Fig. 2, a reduction in t he pavement thickness from that deduced from Fig. 1 or Fig. 3 may be penn issible. It i s recommended that pending further experience an equivalency factor of 1.5 for bituminous macadam a n d 2 fo forr dense bituminous macadam might be utiuised i n design to equate the thickness of t he bitumen bound-layer (provided. i n addition t o the minimum bituminous surfacing shown in Fig. 2) to that of conventional water bound macadam construction. Built-up spray grout to the MOST Specification, will however, b e regarded as equivalent t o conventional granular construction. <<
It is emphasised that t he above equivalency factors are only asuggestion which ha s to b e corroborated and modified i n the light of further study a n d future field performance.
IRC IR C 371984
42.5. When semi-rigid materials such a s lean cement concrete, lean cement-flyash concrete are used in flexible constnic lions, this method of design is not strictly applicable. However, in the absence of an established procedure for the design of composite structures, the thickness of lean cement ith this methed concrete-base/sub-base may be designed for the present s~ using an equivalency factor of 15. The thickness of the serni’rigid layer so obtaIn obt aIned ed sha shall ll be che checke cked d for adequacy adequacy by cal calcul culati ating ng us ult ultima imate te load equations a s per the procedure described in carrying capacity using Meyerhof equations FRC:74- 1979 ‘Tentative Guidelines for IRan Cement Concrete and Lea.n Cemcnt~FlyashConcrete a s a Pavement Base or Sub-base.
42& For roads carrying light t o medium traffic soil-cement bases
2 at 7 days age) ma) he used (having an average, crushing strength of 20 kg/cm when suitable granular material is not available or wher wheree th thee us usee of soilcement is more economical and convenient,
4.3. Bituminous Surfacings Thee surfacing consists of a wearing course or a binder coursc 4,3,1. Th plus a wearing course depending up.n the traffic t o be carried, The most common ty used wearing courses comprise surface dressing, op.. n-graded premix carpet, mix seal surfacing, semi-dense carpet a n d a.sphaltic concrete. For binder courses t h e MOST Specification prescribes bituminous macadam macad am constr construction uctionss of 50 mm and 75 mm thickness, The mix has low binder content and high voids an and d is thus not impervious to water, Furthe.r th e of high high voids is reduced stiffness and increased stress concentrations. effect of From fatigue considerations t h e detrimental effect of voids is more. apparent at low temperatures. On the other hand during prolonged h ot spells t h e average pavement temperatures a r e very high and consequently such a mix will thee use of bituminous operate over a very l ow stiffness range. Hence, th macadam binder courses t o th e MO MOST ST Specific Specificatio ation n may desirably be restricted t o roads designed to carry upto 5 msa. Dense bituminous macadam binder courses are recommended forroads designedto carrymore than S msa. A properly designed dense bituminous macadam mix or a ‘recipe mix’ may h e adopted. 4.12. Recommended surfacing materials a n d thickness in terms of t h e cumulative standard axles to b e carried during th e design life are given i n <<
18
[FtC: 37~1984
functiona ionall and Fig. 2. The suggested surfacings are a desirable minimum from funct structural requirements a n d should n o t b e assigned higher equivalency in relation to other component layers in proportioning the overall structural thickness of t he pavement. 4.3.3. Choice of appropriate type of bituminous wearing course for flexible pavements becomes necessary in several cases such as new pave ments, ren ew ewaa l an and d pav pavem ement ent rehabilitation. Th Thee type of wearing course will depend on several factors like design traffic over the service life, the type of c ourse provided, t he fact whether the pavement is to be built up bas~’bindercourse i n sta stages ges,, rai rainfal nfalll and other related factors. The recommended type and thickness of wearing course under different situations are indicated in Table 3 . Structural section under Fig. 2 ma mayy b e read i n conjunction with this table. These have been developed from present knowledge and ma mayy b e modified if the environmental conditions and experience so justify.
4.3A. For heavy snow precipitation areas whe here re sn snow ow clearance bus-stops s-stops and operations may be mechanised, as well at locations like bu roundabouts consideration ought to b e given to t he provision of dense asphaltic concrete in single or multiple courses, so as t o render the surface more stable a n d waterproof.
4,3.5. As a rule the laying of a permanent wearing surface should n ot be delayed if close control over materials and methods of construction has been exercised. But when a pavement i s being built i n stages, or when close control during construction i s n o t possible, a temporary surfacing such as single coat surface dressing might be provided at the outset so as t o allow further consolidation of t he underlying structure to take place under traffic a n d defective areas to show up which could b e rectified a t th thee time of final surfacing, which should follow a s soon as possible. In no.case traffic shall be allowed on t h e bituminous macadam binder course directly.
43.6. When the wearing surface consists of thin surface dressing or open-graded premix carpet of upto 2.5 cm thickness, th thee th thickness ickness of surfacing should not be counted towards the total thickness of the pavement as t he surfacing will then be purely for wearing and will not be adding t o structural capacity of the pavement. <<
37-1984
3-SH SHOWING OWING TH THEE RECOM RECOMMENDE MENDE D TYPE AND flBCKNF.SS OF BITUMINOUS WEARING LE 3COURSES FOR FLEXIBLE PAVEMENTS UNDER DIFFERENT SITUATIONS Type of base/binder Type of Bituminous course (top layer wearing course with adequate pavement thickness for the cumulative standard axles (CSA) shown in Cot. 5.)
2 ranular base cluding water und macadam/wet sts macadam
ihup spray grout USG) Base
Annual rainfall Low (L) less than 1500 mm; Medium (M) 15(10-3000 mm and High (H) more than mm.. 31100 mm
3
4
1~sign traffic for traffic for
Correspo-
nding** in service life traffic terms of of the the pavement commercial ((5A in vehicles! day millions)
5
6
(i) Two coat surface dressing (ii) 20mm premix carpet (P.C.) plus liquid sealcoat (iii) 20mm PC. plus sand seal coat (iv) Mix seal surf surfacing acing (20 mm) Type ‘A’ or ‘B’.
LandM
0.50
540
L,MandH
510.0
5800
LandM
l0.0
800
L,M and H
510.0
800 80 0
(i)) 20mm (i 20mm P.C. plus liquid seal coat (ii) 20mm P.C. plus sand seal coat (iii) Mix seal surfacing
MandH
l0.0
800 80 0
LandM
10,0
5800
L,MandH
510.0
800
L,MandH
15.0
1200
(200mm)Type’A’ o r ‘B’ tumen Penetration acadam Base shed Cement ncrete Base tuminous Macadam se/binder course
<<
Same a s a t SI. No.2 above, Same a s a t S I. No. 2 above. (i) Semi dense bituminous concrete (Seani dense carpet) (a) 25 (a) 25 mm (1,) 40mm (ii) 20mm Premix carpet with liquid seal coat (iii) Mix seal surfacing (20mm) Type ‘A’ or ‘B’
‘~1
[RC: 37-1984
6. Dense B itum inous Macadam (DBM)
B itum inous concrete (Asphalt Concrete)
(i) 25mm
)L,MandH
~15.0
51200
(ii)4Omm
Notes: ~‘~‘
From the design traffic in CSA in Cot, 5, the present traffic in terms of commercial vehicles/day in Col,6 has been calculated for the case of 2-Lane road, design Life 1 0 years, construction period 2 years, VDF = 2.5, growth rate = 7$ per cent, and lane distribution=75 per cent
In applying applying the reco recommenda mmendations tions contained in the Tab Table, le, ‘the following points should be specially kept In view:
(I)
The pavement should be structurally adequate an and d stable for the design traffic.
(ii) (i i) As a ge gene nera rall nale, the pav paveme ement nt should should be designed for a service life ofat least 10 years. in cases where a pavement Is decided to b e developed in stagea, the iiurfaclng forr the design stage. should correspond to that fo (ill) As far as possible, wearing course amenable to laying with paver-finisher should be adopted over paver-finished bas base/binder e/binder co course. urse. nott b e provided dIrectly over (iv) Expensive surfacings like bituminous concr concrete ete should no granular bases or buil built-u t-up p spr spray ay grout/penetration macadam.
(v)
Built-up spray grou grout, t, w1~e w1~ere reprov provided, ided, should not b e in more than one 1ayer~
(vi) The renewal wearing course should b e related to the design traffic and should be of the type not inferior to that of of the the existing one.
(vii) The design traffic should b e in tarsus of of cumulativestandard cumulativestandard axles (CSA) over the service servi ce life calculated in accordance with the metho method d given given Ira [FtC : 37-1984.
<<
C :37-1984
S. URAINACE MEASURES
cann be serio 5.1. The performance of a pavement ca serious usly ly affected if dequate drainage measures t o prevent accumulation of moisture i n the avere n t structure are n ot take takenn . Some Some of the the measures to guard against peer rainage conditio conditions ns are: maintenance of transverse section i n good shaje to easonable crosslail so a s t o facilitate quick run-off of surface water~anti rovision of appro appropria priate te su surface rface and sub- surface drains where necessary. rainage measures are especially important when the road i s i n cutting or low w permeability soils or situated i n a h eavy rainfall/snow precipi iautht on lo i on area. farr 5.2. On new roads t h e a i m should b e . t o construct the pavement as fa bove, the water table. as economically practicable. The difference be vee.n he fOrmation level and t h e level of water table/high flood level should, owever., not be less than 0.6.1 m. I n water logged areas9where t h e suhgrade i s saturation, tion, consideration should be given to th e i thin th e zone of capillary satura nstaliatton of suitable capillary cutoffs** a t appropriate level underneath t he... avement.
5.1 When the traditional granular construction is provided on a. elatively l ow pc.rmeability subgrade, the granular sub-base should ix. cxnde.d over the entire formation width (Fig. 4) i n order t o drain t h e pavement tructural section. Ca Care re should should be exercised t o ensure that ililss exposed end.s do ot get covered Thee trench type section should n ot covered by by the em emba bank nk~ ~ . ment soil. Th .ment e adopted i n any case as it would lead t o t h e entrapment of water i n th e avement structure~.
Drainage of t h e pavement structural section c a n b e greatly improved graded ed ma material terial)) which rmeabilii biliiy y draina drainage ge layer (open grad y providing a high p. rmea . an be substituted on a centimetre for centimetre basis for t h e granular subase, Aggregates meeting th e following criteria a r e regarded a s very good << rainage materials:
D 55<4 55<4 D 15 15 D2)2,5 mm
IRC IR C :37-1984
means t h e size of the sieve that allows 85 per cent by weight of t h e material t o pass through i t . Similar i s t h e meaning OfDai and D
2
Thee drainage layer when placed on soft erodibie so Th soil ilss sh shou ould ld be underlain by a layer of filter material t o prevent th e intrusion of soil fines into t h e drainage layer (Fig. 4). 5.4. \Vhere large inflows are t o be taken care of, an adequately designed sub-surface drainage syste.m consisting of a n open graded drainage layer with collector and outlet pipes should be provided. Th Thee system should be des desig igned ned on .a. rational basis usin using g seepag seep agee principles t o estimate th e inflow quantities and the..: outflow conductivity of the drainage system. It should be ensure.d that the outflow capabilities aithe system are at least equal t o t h e total inflow so that n o free. water ac.cumulate.s i n t h e pavement structural section. S ub-surface drains should conform t o th e requirements prescribed i n Clause 309.1 of t h e MOST Specification for Road and B ridge Works. 5. Drainage of existing pavement of ‘Trench type’ stxtion on l ow cann b e . improved by providing a contin permeability sub-grades ca continuous uous draina drainage ge layer of 10-15 cm thick ness under the shoulders a t the suhgrade level or b y providing a combination of longitudinal and lateral drains, th e latter spaced at.5 t o 6 t m intervals. Th Thee drains a r e cut thro throuugh the shoulders upto the with h coa coarse rse drainage material. subgrade level and hackfilled wit .5
5.6. Very ofte often, n, water water ent enters ers th thee ba base, se, sub-base o r th thee sub-grade a t t h e junct junction ion of t h e verges a n d the bitu bitumino minous us surfacing.. To counteract t h e harm ful effects of this water, it i s recommended that the shoulders should be well-shaped well -shaped an and, d, if possible, construc constructed ted of impermeable material.. With the. same intent it is suggested that as far as practicable, and i n any case. on major througgh road throu roads, s, the base should be constructed 30-45 cm wider than t h e reiuired bituminous surfacing so that. the run-off water disperses harmlessly well clear off th e main carriageway. .5.7. Shoulders sh shou ould ld be accorded special attention during subsequent ma.tenance operations too. They should be dressed periodically so that they always conform to th e requisite crossfal.i and are n ot higher than t h e level .of << t h e carriageway at any time.
IRC IR C :37-1984
~ITUI~INOUS
GRANULAR
SURFACING
8AS~
SUB-8ASE
(a) ROAD ON FILL (NO SUB- St~FAc~ D RAIN~
r $fl’U~9~NOUSSUP F A C 1 MG lr~,u~uLAR eA.s~
t.AYtR ~
~J~SASE
I WNt~~,OUI~O
I
(bI ROAD IN CUT
IKO SUB-
OUTLET PIPE
C%U-ICTOR PIPI
SURFa~DRA~N5I
T EX’rENOUNOCP ...~
SHOULDERS ~ REQUIRED
ll,op~~
$JB- BASE LA’ItR OPMATERIAL t’FILTER IWN IW NIRE
PIOUrR PIOU rRID ID I
(cI DRAIN~6GESYSTEM WITH SUB-SURFACE DRAINS Fig 4. Dratnage of of pavements pavements on impermeable subgrades ~Not to scale)
<<
tRC : 37-1984
6. DESIGN IN FRO FROSTST-AFF AFFECT ECTED ED ARE AREAS AS
6.1. In areas susceptible to frost action, the design will have t o be related to actu actual al depth of penetration a n d severity of the frost. At the suhgrade level, fine grained clayey and silty scils are more susceptibl susceptiblee to ice formation, h ut freezing conditions could alsodevelop within the pavement structure if water had a chance of ingress from above. One remedy ag 6.2. One agai ainst nst frost attack i s t o increase t h e depth of may y n ot penetrat ation ion,, bu butt th this is ma construction t o correspond t o the depth of frost penetr always be economically practicable. As a general rule, it would be inadvisable t o povide total thickness less than 45 cm even when t h e CBR value of t h e subgrade warranted a smaller thickness. In addition the materials used for resistant. nt. building up the crust should b e frost resista
6.3. Another precaution against frost attack i s that water should n ot be allowed t o collect at t h e subgrade level which may happen on account of infiltration through the pavement surface or verges or due t o capillary rise cann be prevented by subsoil from a high water table, Whereas capillary rise ca cann be ch drainage measure.s and cutoffs, infiltering water ca check ecked ed on only ly by providing a suitable wearing surface. METHOD D 7. WORKED EXAMPLES ILLUSTRATING THE DESIGN METHO Example
I..
Design or pavement for the ttslI design life that Is without consldertng stage
construction DATA:
(i)
Two lane single carriageway
(ii) Initial traffic in the year of
=
completion of construction
1000 CV/day Sum of both directions
(iii) Growth rate per annum
= 7.5 per cent
(iv) Design life
=
(v) Vehicle damage factor
= 2.5 (standard axles
t5yeara per commercial vehicle)
(vi)) Des (vi Design ign CBR of subgrade soil
= 4percern
Dt.sIcN C&.cutsnoNs
(i) <<
tnitial traffic in design lane
Initial traffic a Distribution
=
factor as per pera 3.2.3.2.
= 750 CV/day
1000 a 0.75
i7~1984 (b~ calcolse cumulative number
cateredd of standard axl axles es to be catere
=
1 8 msa
for in the design
(Equation given in para 3
3.1.)
(iii) Total pavement thickness for
CBRr=4percent,
= 680mm
Traffic = 1 8 maa (Fig.l)
(iv) Pavement Composition:
From Fig.. 2, Thickness Combination Block (a) Bituminous surfacing
:
130mm consisting of 40mm AC wearing course +
90mm DBM binder course (b) Road base
:
250mm WBM
(c) Su&base
:
300mm granular material of CBR not lest than 30 per cent in the top 150mm portion and of CBR not less than 1 0 per cent in the lower portion (pars.
4.1.1.)
ample: 2:
:
Design of pavement pavement providing for stage construction
TA:
(i)
Data a s for Example
I
(ñ) I> initia tiall sta stage ge per period iod of 5 years and rpecify the strengthening I>.. sign the pavement for a n ini
layer to b e added after the initial stage traffic has been carried. S tON CALCtJt.A11ONS
(i)
initial uaffic
itt
design
=
750 CV/day
=
1 8 msa
lane (Example 1)
(ii) Cumulative number of axles les to b e carried standard ax over the design life of 1 5 years (Example 1)
(iii) Calculate cumulative number
of standard asks to b e carried over the initial stage period of 5
years (Equation givr’n in pans 3.2.2.)
<<
= 4 msa
ERC :37-1984
(iv) Total thickness for 15 years
=
680mm
life (Exa (Example mple 1) (v) Sub-base thickness for the
fulllifeofl5yeaes(As = 300mm
worked out in Example 1)
(vi) Design thickness for S years life, CBR= 4 per cent, = 550mm
Traific = 4 msa (Fig, I)
(vii) Pavement composition for the initial stage period of
5 years: (a) Bituminous surfacing
=
20 mm PC wea wearin ring g c.ossrse
(b) Road base (ror 4 rosa from Fig. 2)
=
2SOmmWBM
(c) Sub-base (Provide thickness
= 300mm granular material of CBR
required for the full design
not tess than 30 per cent in the top
life of IS years,
150mm portion and of CBR CBR not
pars 4)
less than 10% us the lower portion
5500 mm 55
Total:
Check with resp Check with respect ect to the the
=
O.K.
total thickne~sa s per step (vi) (viii) Extra thickness to b e added
= 4OmmAC
after the ini initia tiall sta stage ge tra traffi fficc
90mm DBM
has been carried. Ultimate
130mm
thickness required-thickness provided initiatly=680.550= l3thnm.
‘l’he existing surface should be rectified to permissible
tolerance toler ance prior prior to laying of the stren strengtheni gthening ng course
E.xansple3: Design
or strengthening measures
DArk the assess assessmento mentof f the On thebasis of the the existing condition of a certain NH section, a decisionhas suitable itable overlay to carty 1 0 msa in the neat five years after been taken to strengthen itit.. Design a su construction. The existing pavement is of 380 mm granular thickness with thi thin n bituminous surfacing. Su Subgrade bgrade CBR is 5 per cent <<
R C :37.1984
DmstoN CALQtI .AT1ONS: (i)
Ded De duce li liffe of existing structure
=
0.Smaa
=
lOmsa
=
10.5 rosa
=
560mm
=
180mm
new w as asem emen entt a s a ne thickness ness design curve for CR From thick S
per cent in Fig.
1
read life (rosa)
corresponding to 380 mm thickness (ii) Future traffic to b e carried (iii) Design traffic fur determining
overall thickness (i) + (ii)
(iv) 1~os.alpavement thickness for C13R = 5 percent
Traffic = IC. 5 rosa (Fig. 1) (v) Overlay thickness required (Total design thickness-
liaitting-thiekness)
Providing surfacing
25mmAC +80mm DBM
correspon corr esponding ding to 10 rosa, Fig. 2
+
(vi) Overlay composition
=
Total:
<<
75 mmWBM
180mm
IRC :37-1984
Appendir I
PREPARATiON O F LABORATORY TEST SPECIMENS GENERAL
1. Wherever possible, the test specimens should be prepared by static compaction, but if n ot possible, dynamic method ma may y be used a s a n alternative, STATIC COMPACTION
2 . Th Thee weight of wet soil at th e required moisture content 10 give t h e intended density when occupying t h e standard test mould i s calculated a s follows Volume of mould Weight of dry soil Weight of we wett soil
Where
d m
=
= =
=
=
2209 cc 2209 d gm 100+ m ~ 2209 d gm required dr dryy density in gm/ce required moisture content (per cent)
3 . Th Thee soil is broken into lttmps, any stones larger than 20 mm being discarded. S ufficient quantity of t h e soil i s mixed with water t o give t h e required requ ired mo moistu isture re content. Th Thee correct weight of wet soil i s placed in t h e niould. Alier initial tamping with a steel rod, a filter paper is placed on t op of t h e soil, followed by (h (hee 5 cm displacer disc, a n d t h e specimen corn pn:~ssed i n t h e compression machine unlil the 101) of t h e displacer is flush with th e t op of the. collar, Th then en relea released sed.. In some Thee load is’ held forabout 30 seconds a n d th soil types where a certain amount of reb re~ ~ rebou ound nd occurs occurs it ma may y h e necessary to re apply load t o force th e displacer di.se slightly below t h e t op of th e moLl,ld so that on rebound t h e rtght volume is obtained. t)YNAMIC i’OMPACTION
e d with water to give the reqtiired tnoisturc content, ‘The soil ismi~ a n d then compacted into t h e mould i n 3 layers us.. .ing a standard soil rammer. << ~ t o m on onpp tc lion t h i sotl i s trimmed Ilttsh wtttt th e t op ol t h c rnoaltl with th i 4.
IRC :37’t984
help of a metal straight edge. Th Thee mould is weighed full a n d empty to enable determination of wetbulk density, a n d from it, knowing th e moi moisture sture cont content, ent, thee dry density to be calculated. th
5. Farther specimens, a t the same moisture content, a r e then prepared t o different dr dryy densities by varying t h e number of blows blows applied t o each layer ‘ o f soil so that t h e amount of compaction that will [‘illt h e mould uniformly wett soil (vide para 2 above) i s known. with calculated weight of we
<<
Appendix 2
SPECIAL POINTS RELATING TO DESIGN O F PAVEMENTS O N EXPANSIVE SOILS
Potentially expansive so soils ils su succh as black cotton soils are mont,ntorillonite clays and a r e characterised by their extrem extremee ha hardn rdness ess and deep cracks when dr dryy and with tendency for hea heavin ving g during t h e process of wetting. Roadbcds made up of such soils when subjected t o changes i n moisture co con ntents due t o seasonal wetting and drying o r d ue to a n y other reason undergo volumet volu metric ric cha chang nges es leading to pavement distortion, cracking and general unevenness. In semi-arid climatic conditions with pronounced short wet and long dr dryy periods, significant fluctuations i n t h e subgrade moi moisture sture cond conditio itions ns occur which aggravate th thee prob problem lem of sw swelli elling ng and shrinkage. Du Duee recognition of these problems at the design stage itself is required so that counter measures could be devised and incorporated i n the pavement structure. A proper design incorporating t h e following measures ma may y con considera siderably bly minimise t h e problems associated with expansive soils: SUBGRA GRADE DE MOI MOISTU STURE, RE, DEN DENSITY SITY AND DESI DESIGN GN CBR 1. SUB
The amount of volu volume me c ha nge that occurs when an expansive soil road bed is exposed t o additonal moisture depends on t h e following: (a)) the dry density of the compacted soil (a (Li) the moisture content (c) structure of soil and method of compaction Expansive soils swell very little when compacted a t low d en sities and high mo moisture isture but swell greatly when compacted at high densities and l ow moisture. Hence, wh where ere th thee probability of moisture variation i n the subgrade is high, it i s expedient t o compact the soil slightly wet of the field optimum moisture content determined on the basis of a field trial, Experierce shows expansive ive soil soilss a t O MC that generally it is not practicable to compact expans is,, therefore, necessary t o study ititss determined by LaboratoryProctor Test It is field moisttire-density relationship through compacting the soil at different moisture contents and under the same number of roller passes. A minimum density corresponding to 9 5 pe perr cent of the standard proctor density should attain ained ed in the field, be att 31
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DESIGNCBR
Thee pavement thickness should b e based on a 4-dat soaked CER Th luee of t h e soil remoulded at placement density and moisture content lu certained from the field compaction curve. 2. BUFFER LAYER
There is a definite gain in placing the pavement on a non-expansive
hesive soil cushion of 0.6-1,0 m thickness~,I t prevents ingress of water i n eounteractss swelling and secondly even e underlying expansive soil layer, eounteract t he underlying expansive soil heaves, the movemen t will will b e more uniform d consequently more tolerable, However, where provision of non-expanve buffer layer is n o t economically feasible, a blanket course of suitable aterial a n d thickness as discussed in para 3 below must be provided. BLAN ANKE KET T COUR COURSE SE 3. BL
A blanket course of atleast 225 mm thickness andcomposed of eoarse/ edium sand or non-plastic moorum having P1 less than 5 should be provided the expansive soil subgrade as a sub-base t o serve as an effective intrusion rrier. The blanket course should extend over the entire formation width, Alternatively, lime-stabilised black cotton sub-base extending over provided ded together with measures fbr e en enti tire re fo formati rmation on wi widt dth h may be provi ficient drainage of t he pavement section. 4. DRAINAGE
Improvement of drainage c a n significantly reduce ‘the magnitude of asonal heaves, Special attention should, therefore, b e given to provision of od drainage measures a s also discussed under Section 5 (Drainage Meases). The desirable requirements are: (a) Provision must be made for the lateral drainage of t he pavement structuntl section, The granular subbase/base should accordingly be extended across th e shoulders, refer t o pam 5.3 of Section 5
(Drainage Measures).
(b)Normal camber of 1:40 for t h e black t op surface and a cross slope
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of 1:20 for the berms should be provided to shed off surface run-off
quickly. (c) No standing water should be allowed on either side of t h e road e mb a n kment, (d) A minimum height of I
m
between th e subgrade level a n d the
highest water level should be ensured. 5. BITUMtN BITUMtNOUS OUS SURFAC SURFACING ING
Desirably 40 mm thick bituminous surfacing should be provided t o prevent ingress of water through surface. 6,SHOULDERS
Shoulders should b e made up of impervious material so as n o t to allow water topermeate into the body of the pavemenL Lime stabilised black cotton soil shoulder of 15-20 cm thickness ma may y serve the purpose economically.
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