Site Investigation for Civil Engineering Projects By Ir. Neoh Cheng Aik E-Geo Consultant Sdn Bhd
SCOPE OF DISCUSSION 1.
INTRODUCTION • • •
2. 3.
4.
5.
General What is SI Role of SI in Geotechnical Design
WORK PROCEDURE FOR SI PLANNING SCOPE OF SI • What needs to be known • SI Methods • Criteria to determine depth core length • Examples INTERPRETATION • Field & reported borelogs • Property correlations • Groundwater • Miscellaneous CONCLUSIONS
GENERAL 1. Geotechnical Engineering (3 major areas) • •
Geotechnical Engineering is a science, but its practice is an art SI & soil properties (Significance?) • • • •
• •
Basic, index & chemical properties Engineering properties Typical properties of typical formations Planning of SI & methods
Soil Mechanics Principles Applications – Design & Construction
2. Difference between geotechnical & structural design 3. Learning curve (easy to learn & slow to master) 4. Inadequate SI & poor interpretation – main causes for failure? Examples? Liabilities?
WHAT IS SI? • Scientific exploration with predetermined objectives • Know something first through desk studies & site visit about the site & project before we can determine the purpose of SI & identify the possible geotechnical problems • Subsequently, we plan scope of SI to obtain the necessary parameters to verify, assess & quantify the geotechnical problems identified • Prerequisites to qualify to plan SI?
WHAT NEEDS TO BE KNOWN? •
What is known; what is not known; & what needs to be known? Circle of
?
?
“KNOW ALL”
? ? What needs to be known
? What is not known about the site
? ? *
? Circle of what is known
Those who know NUT and know not that they know NUT will not know what Needs to be known.
EXTENT & SCOPE OF SI REQUIRED FOR A PROJECT DEPEND ON: • Experience & knowledge of designer about the anticipated geotechnical problems, the project brief & available SI facilities & methods • Local geology & typical problems • Historical use of the site: Why significant? • Treacherous Grounds: uncontrolled fill, limestone formation, boulders & corestone abutment ground, etc. (significance?) • Relevant information about the project, etc.
EXAMPLE 1: A 4-Storey JKR Standard RC School Block in Klang District
• Do you know the column loads & characters of RC framed structures? • Do you know the site & layout conditions/constraints? • Do you know the site geology & typical geotechnical problems? • Do you know what parameters are required? • Do you know what SI methods & tests to procure the required parameters
EXAMPLE 2: A hill is to be cut to a depth of about 24m SCOPE OF SI? • Answer 3 questions: what known; what unknown & what needs to be known? • Influencing factors affecting FOS? • Geological information of the hill? • Weathering profile (discontinuities, relict joint, suitable minerals, shear strength & deformation, permeability) • Groundwater conditions? • Other critical information?
PLANNING SCOPE OF SI • • • • • • •
How many BH or other SI methods; locations? Criteria of terminating BH? Field test: type, criteria & frequency? Sampling: type, criteria & frequency? Reference notes: for building & road projects Documentation: Drawings, BQ, Spec, etc. Examples
BASIC SCOPE OF SI WORKS
SI
DESK STUDIES & SITE VISIT
BORING
SAMPLING
FIELD TESTING
LAB. TESTING
PURPOSE & IMPORTANCE OF EACH ACTIVITY?
BORING
TYPES OF BORING:
SPECIFICATIONS & STANDARDS
Auger boring Percussion Wash boring Rotary boring Foam drilling Tools & equipments; flushing medium?
PURPOSE, APPLICATIONS & LIMITATIONS?
SAMPLING
DISTURBED SAMPLES • • •
WASH SPT BULK
UNDISTURBED SAMPLES
•
• • • • •
•
THIN-WALL PISTON MAZIER BLOCK FROZEN
•
CONTINUOUS SAMPLES WATER SAMPLES ROCK SAMPLES
• PURPOSE, APPLICATIONS & LIMITATIONS?
COMMON SAMPLERS TYPE OF SAMPLERS (Purposes?) 1.
Open drive samplers – Split-spoon for SPT – Thin-wall sampler – Thick wall sampler (50mm, 75mm, 100mm, 150mm)
2.
Thin-wall sampler with stationary piston (50mm, 75mm, 100mm, 150mm)
3.
Denison Sampler (double tube with thin-wall tube)
4.
Mazier Sampler (74mm)
5.
FOIL CONTINUOUS SAMPLERS
6.
BLOCK SAMPLING
7.
ROTARY ROCK CORE SAMPLERS
FIELD TESTING
• • • • •
SPT VANE SHEAR PACKER PERMEABILITY PRESSUREMETER
• • • •
DUTCH CONE PIEZOCONE MACKINTOSH PROBE JKR PROBE
• • • • • •
• •
SPEC. & STANDARD PURPOSE, APPLICATION & LIMITATION?
TEST PIT CBR PLATE BEARING FIELD DENSITY GEO PHYSICAL SURVEYS SPECIAL TESTS
APPLICABILITY OF COMMON FIELD OR INSITU TESTS FIELD TESTS
1.
Soil
Soil
Rock
SOIL TYPE
SOIL PARAMETERS
type
Profile
H.Rock
S.Rock
Gr
Sand
Silt
Clay
Peat
Ø
Cu
Mv
Cv
K
X A B A B C
C B A A A C
X X X X X X
X B X X X X
C B B A C C
B A A A A A
B A A A A A
B A A A A A
B A A A A A
X B C B B B
B B B B B C
X X C A C X
X X C A C X
X X X B X X
Penetrometer 1.1 1.2 1.3 1.4 1.5 1.6
JKR Probe SPT DS (CPT) Piezocone (CPTU) Flat Dilatometer Resistivity Probe
2
Vane Shear
B
C
X
X
X
X
B
A
B
X
A
X
X
X
3
PB Pressuremeter
B
B
C
A
B
B
B
A
B
X
B
B
C
X
4
SB Pressuremeter
B
B
C
B
B
B
B
A
B
B
B
B
B
B
5.
Continuous Soil Sampling
A
A
X
B
B
A
A
A
A
C
B
B
B
C
Legends:A B C X
= = = =
suitable/useful moderate doubtful not suitable
φ Cu Mv Cv
= = = =
effective frictional angle undrained strength coef. of volume compressibility coef. of consolidation
K
=
coef. Of permeability
LABPRATORY TESTING
CHEMICAL PROPERTIES
BASIC INDEX PROPERTIES
• Organic, SO3-
• Colour, S.G., density, LL, PL, PI, SL, PSD, etc.
& Cl-
• PH value, etc.
SHEAR STRENGTH • • • • •
UU, CIU, CD Shear box Compressibility Compaction CBR
OTHER TESTS • • • • • •
1-D Oedometer Rowe cell Compaction Permeability Dispersibility Hydraulic cell
• PURPOSE, APPLICATIONS & LIMITATIONS?
ROLE OF SI IN GEOTECHNICAL ENGINEERING DESIGN
INTERPRETATION JUDGEMENT
SI
SOIL PROPERTIES
GROUND BEHAVIOUR DEFORMATION DISPLACEMENT STABILITY
CODES OF PRACTICE • FOUNDATIONS, BS 8004 • ANCHORS, BS 8081 • EARTHWORKS, BS6031 • REINFORCED FILLS, BS 8006 • GEOGUIDES OF GEO HONG KONG • GROUND IMPROVEMENT
MODELLING PREDICTION
GROUND CHARACTERISATION
ENGINEERING PERFORMANCE
• • •
ENGINEERING PROPERTIES CHEMICAL PROPERTIES BASIC & INDEX PROPERTIES
• •
MASS PROPERTIES TYPICAL & GENERALISED SUBSOIL PROFILE & PROPERTIES OF TYPICAL GEOLOGICAL FORMATIONS; MANMADE FILL, etc. ENGINEERING GEOLOGY
•
SOIL & ROCK MECHANICS • EFFECTIVE STRESS THEORY • SEEPAGE THEORY • STRESS DISTRIBUTION • LATERAL PRESSURE • BEARING CAPACITY • COMPRESSIBILITY • COMPACTION, etc.
INSTRUMENTATION FOR • PORE WATER PRESSURE • EARTH PRESSURE • DISPLACEMENT (SURFACE & SUBSURFACE) • INTERNAL STRESSES • VIBRATION
GROUNDWATER MEASUREMENT 1.
TYPES OF GROUNDWATER • • •
Static WT/phreatic level/main WT Perched WT Artesian water
2.
SIGNIFICANCE FOR
3.
• Pile installation • Deep excavation • Slope stability • Tunnelling, etc. METHODS • • • • •
4.
Observation well Simple Standpipe Casagrande standpipe Pneumatic piezometer Hydraulic piezometer, etc.
CASE HISTORIES
LEGEND: MEASURED WT
RAIN RUN OFF
PERCED WT
STREAM
AQUICLUDE ARTESIAN WATER
INFILTRATION
PERCOLATION
UNCONFINED AQUIFIER (FREE WATER)
ACQUICLUDE
AQUIFIER
ACQUICLUDE
FREE WATER SURFACE
13 10
15
1
8 9 3
6 2 15
4
6 5
Instrumentation
Application
1
Inclinometer casings
Monitoring of earth lateral movements in sliding areas
2 3 4
Stress gauges Electrical piezometers Casagrande piezometers In-place inclinometers Load cells
Monitor ing strain and stress development in the stressed member of piles Monitoring of soil pore pressure and control of over pressure Measurement of water table level Monitoring of landslide areas and stability of natural slopes Measurement of anchor tensioning or loading at the head of tie-back
Flow meters Surface clinometers Borehole ex tensometers
Drainage flow control Monitoring of rock mass inclination movements and block tilting Monitoring of retaining wall stability
Wire crackmeters Rain gauges Total pressure cells
Monitoring cracks and movements in rock masses Monitoring of rain falls Measurements of soil stress and pressure on ground or retaining w alls or piles
5 6 7 8 9 10 13 15
15
APPLICATION OF GEOTECHNICAL INSTRUMENTATION
SPT 1.
SPEC. & STD. (BS, ASTM) • • • •
2.
APPLICATIONS & LIMITATIONS • • •
3.
Soil types Correlations Shortfalls
SPACING/INTERVALS OF TESTING • •
4.
Equipment set Hammer, drop, rod Split spoon sampler Records & procedure
Type of investigation & purposes Criteria & procedure
CASE HISTORIES
COMMON MALPRACTICE IN SPT/SI
* SPT taken without adequate & proper cleaning by clean water
* SPT taken constantly at 1.5m intervals; not at change of soil strata * SPT hammer weight not within 63.5+_ 0.5 kg; hammer not fully made of steel; drop height less than 76+_ 2 cm after repair/retread. * Drilling in sandy soils without quality bentonite * Use casing and not proper drilling rods to advance boreholes * Samples from SPT split sampler not sealed in container with proper labels & storage * Use blunt SPT drive shoe * Mark SPT penetration on rod without ruler or chalk * Soil description & record of SPT blow counts on palm/shirt/casing & not proper paper *Drive rod for SPT not straight or inadequate stiffness; for depth>20m, BWNW rods shall be used * Untrained supervisor or foreigner supervisor who cannot communicate well
ROCK CORING 1.
PURPOSE & APPLICATIONS: •
Identification, description & correlations
2.
CORE BARREL: single, double & triple
3.
CORE BITS: tungsten, surface/impregnated diamond
4.
CORE RECOVERY RATIO, RR = (Total core obtained)/(length of run)
5.
RQD = (summation of rock core > 100mm)/(length of run)
6.
RQD < 25%
VERY POOR
RQD = 25 – 50%
FAIR
RQD = 50 – 75%
GOOD
RQD = 75 – 100%
EXCELLENT
ROCK DESCRIPTION: STRENGTH & WEATHERING GRADE UCS < 5 N/mm2
Weak
UCS = 5 – 12.5 N/mm2
Moderately Weak
UCS = 12.5 – 50 N/mm2
Moderately Strong
UCS = 50 – 100 N/mm2
Strong
UCS = > 100 N/mm2
Very Strong
ZONES
1. Implication of Location of WT & slope stability 2. Usual location of groundwater 3. Discontinuities & relict joints 4. What relevant soil/rock properties (tests) are necessary for slope stability analysis?
A&B VI
V IV III II
I
Weathered granite showing well defined relict jointing
Weathered volcanic rock showing well defined relict jointing
Granite showing intense weathering along joints
Volcanic rock with staining along joints: Zone D
Completely decomposed seam (Grade V) in slightly decomposed volcanic rock (Grade II)
Moderately decomposed seam (Grade III) in slightly decomposed volcanic rock (Grade II)
Moderately decomposed granite rock (Grade III), 4.65 to 5.55 m Highly decomposed granite rock (Grade IV), 5.55 to 10.71 m
Moderately decomposed granite rock (Grade III), 21.48 to 22.00 m Slightly decomposed granite rock (Grade II), 22.00 to 24.48 m
SOIL IDENTIFICATION & DESCRIPTION • • • •
Purpose & significance Field & lab. techniques BS5930 description of soil Consistency or relative density, fabric if distinguishable, colour, subsidiary, grading, principal soil type & more detailed comments e.g. very stiff dark grey silty CLAY with traces of sand e.g. sandy silty CLAY e.g. silty sandy CLAY (Wrong!)
SOIL CLASSIFICATION • BSCS, USCS, AASHTO • Based on grading & index properties • Coarse grained soil = PSD; fine grained soil = plasticity; How & what properties are influenced by moisture? • Purposes & application? • Design guides based on soil classification
SI RESULTS INTERPRETATIONS •
Scope of factual report: JKR Spec.
•
Scope of interpretation report
•
Field & reported borelog
•
Check borelogs & summary of lab. Test results
•
Discrepancies/compliance with Std/Spec
•
Interpretations: Atterberg limits, compaction test, etc.
•
Typical geological formations; typical geotechnical problems to various types of foundations, etc.
CLAY (%)
4
UP 3/ D5 R=80/80cm
5
P 3/ D6 (Hammer Weight) R=37/45cm
8
(%) 100
0
50
24
26
CHS
Very Soft Grey very clayey fine S AND with some shell fragment and trace of organic matter
0
11
54
35
CI
1.557
27.39
Very Soft becoming soft Grey silty CLAY with lenses of fine sand and organic matter; with occassional shell fragment between 5.0m - 9.0m
0
6
45
49
CE
1.565 2.12
19.31
CI
1.492
31.03
CE
1.568
83.28
10
20
S PT N
30
Very Soft Grey fine sandy silty CLAY with traces of shell fragment and thin layers of organic matter
UP 2/ D3 R=66/80cm P 2/ D4 (Rods Weight) R=35/45cm
7
80 40
50
TRIAXIAL TEST C (kPa)
φ
CONS OLIDATION TEST PC
CC
eO
(°) (kPa) 15
CHEMICAL TEST
0.425 1.472
P 1/ D2 Very Soft (Rods Weight) Grey silty CLAY with trace of fine sand, R=30/45cm shell fragment and organic matter
3
6
60
SILT (%)
2
40
SAND (%)
1
20
Depth of water 16.70m a.s.l.# (19/12/92)
GRAV EL (%)
UP 1/ D1 R=80/80cm
DESCRIPTION OF MATERIAL
LL
Seabed Level (ACD) - 14.50m
W ATER LEV EL:
CHLORIDE CONTENT (%)
TESTING SAMPLING CORING
SYMBOL
DEPTH (m)
PARTICLE SIZE DIS TRIBUTION
REDUCED LEV EL:
BOREHOLE:
SULP HATE CONTENT (%)
PL
ATTERBERG LIMITS MC
P ulau Lumut, Port Klang
Rotary
ORGANIC CONTENT (%)
DATE DRILLED: 17/12/92 - 19/12/92
PE/SI/21/93
TYPE OF BORING:
PH VALUE
LOCATION:
S epakat Setia Perunding
BULK DENS ITY (Mg/m 3 )
Lembaga Pelabuhan Klang
CONS ULTANT:
SOIL CLASSIFICATION
CLIENT:
B6
JOB NO:
UNCONFINED COMPRESSION S TRENGTH (kPa)
Subsurface Investigation and Testing for Proposed West Port (Phase II) Pulau Lumut, Post Klang
SP ECIFIC GRAVITY
PROJECT:
UP 4/ D7 R=65/80cm P 4/ D8 (Hammer Weight) R=29/45cm
0
5
45
50
23
0
160 1.089 1.470
31
0
180 0.778 1.494
UP 5/ D9 R=78/80cm 9
10
P5/D10 (Hammer Weight) R=25/45cm S OILS SYMBOL C=CORING CR=CORE RECOVERY V=V ANE SHEAR TEST
P=S TANDARD PENETRATION TEST N=NO. OF BLOW PER 30cm UP=UNDISTURBED SAMP LE D=DISTURBED SAMP LE
VANE SHEAR:
UNDIS TURB ED REMOULDED
REMARKS: 1. 2.
R -- Denotes Recovery # -- above seabed level
ENGINEERING BORELOG
SIGNIFICANCE OF ATTERBERG LIMITS Plasticity
Shrinkage limit WS
Plastic limit WP
Liquid limit WL
Moisture, MC
•
WL & WP = f(amount & type of clay)
•
PI = f(clay content)
•
High PI = high clay content
•
PI < 30% = sandy/silty soils
•
Soils of high PI can’t be stabilized unless MC is dissipated, very slow due to low K
IC
WL - WN = WL - WP
1.0 I C 0.75 0.5 0.25 0
WS
WP
WN
WL
CONSISTENCY
CU (kN/m 2 ) VS
HARD
> 200
V. STIFF
100 - 200
STIFF
75 - 100
FIRM
40 - 75
SOFT
20 - 40
V. SOFT
< 20
WS
WP
VA
COMPACTION TESTS •
Purposes & applications
•
Interpretation & appreciation Air content
2.2
10% 5% 0%
Air content
2.3
2.1
10% 5% 0%
2.0
2.2
GW
2.1
4.5 kg rammer
2.0 2.5 kg rammer
1.9 1.8 1.7
Dry density (Mg/m 3 )
Dry density (Mg/m 3 )
Saturation line 1.9
SW 1.8 ML
1.7 1.6
CL
1.5
1.6
CH
1.4 0
2
4
6
8
10 12 14 16 18 20 22
Water content (%)
0
5
10
15
20
Water content (%)
25
30
Dry density
Soil A
Z .A.V.
Soil B Soil C
Soaked CBR
Moisture content
Soil A
Soil B
Soil C
Moisture content
OTHER INTERPRETATIONS •
SG = 2.6 – 2.7, usually
•
Soils with SG < 2.6, soil type?
•
Soils with SG > 2.7, soil type?
•
PI < 30%, soil type?
•
Activity, A = PI/(% of clay) Kaolinite, A = 0.3 – 0.5 Illite, A = 0.9 Montmorillonite, A > 1.5
•
Soils with high “A” can absorb more water; more swelling & shrinkage problems; applications?
TYPICAL GEOLOGICAL FORMATION & TYPICAL PROPERTIES 1. Residual soils of granite: •
% of sand/gravel is high
•
WL < 60 %, PI < 30% generally
•
Density = 18 – 20 kN/m3 , NMC = 10 – 30%
•
C’ = 0 – 20 kPa, φ’= 30° – 42°
•
Weathering profile & boulder problems
•
γdmax = 15 – 20 kN/m3, OMC = 10 – 18% (Std. Comp.).
•
Relict joints are preferred water path; have lower shear strength; Significance? How to identify?
•
Common Geo Problems to piling, deep excavation, slopes?
•
Important properties sought in SI?
2. Residual Soil of Meta Sedimentary Rocks: •
Generally WL < 80 %, PI < 40%
•
Density = 16 – 22 kN/m3
•
C’ = 0 – 25 kPa, φ’= 25° – 38°
•
γdmax = 15 – 19 kN/m3, OMC = 12 – 24% (Std. Comp.)
•
Relict discontinuities/beddings/foliations are preferred water path; have lower shear strength; significance? How to identify?
•
Common Geo Problems to piling, deep excavation, slopes?
•
Important properties sought in SI?
3. Soft Alluvial Clay: •
Generally WL = 40 – 140%
•
PI = 20 – 90%, NMC = 40 – 130%
•
Sensitivity = 2.5 – 8, OCR = 1 – 4 (<5m bgl)
•
Cu/Po’ = 0.25 – 0.45 (av 0.33), Cu = 8 – 20 kPa
•
Cc = 0.8 – 3.0 & Cr = 0.05 – 0.1, CR = 0.2 – 0.5
•
Cv = 0.2 – 20m2/yr, Ch/Cv = 1 – 5
•
Cvfield/Cvlab = 1 – 100
•
Muar Flat Trail Embankment Research Findings?
•
Significance & correlations? Common problems for building & road projects?
CONCLUSION •
SI is part of Geotechnical Design. Why?
•
Scope & definition of Proper SI: properly planned, supervised, monitored, directed & reported
•
Important to understand & to identify possible geo problems of the ground to the project before planning scope of SI
•
Important to learn typical subsoil profiles for various typical geological formations/grounds, their typical properties and their usual problems to various types of construction
•
SI → soil properties → Mass properties & ground characterization → Behaviour prediction → Performance
•
Scope of SI planned by different engineers tends to be varied. Why?
The End Thank you for your attention
