GEOTECHNICAL ENGINEERING II (ModuleI PartII – 1)

GEOTECHNICAL ENGINEERING II

MODULE I CHAPTER 2MODULE – I CHAPTER – 2

Site investigation and soil explorationSite investigation and soil exploration

Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode

SYLLABUS - Module I

2. Site investigation and soil exploration:

objectives - planning - reconnaissance - depth

and lateral extent of explorations -methods ofand lateral extent of explorations -methods of

subsurface exploration - test pits - Auger borings

- rotary drilling –Types of soil samples-split

spoon samplers- Standard penetration test-spoon samplers- Standard penetration test-

hand cut samples- boring log - soil profile-

geophysical methods (in brief).

Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode2

OBJECTIVES OF SOIL INVESTIGATION

● Determination of

– The nature of the deposits of soil

The depth and thickness of the various soil strata and– The depth and thickness of the various soil strata and

their extent in the horizontal direction

– The location of ground water and fluctuations in GWT

– Engineering properties of the soil and rock strata by

conducting laboratory tests

– In-situ properties of soil by performing field tests

● Obtaining soil and rock samples from the various strata


Geotechnical Investigation

Preliminary Investigations

Detailed Investigations

Reconnaissance


RECONNAISSANCE

● Inspection of the site and study of the topographical

f tfeatures

● Study of maps and other relevant records.y p

● Collect details about proposed constructions

C ll t l d i ti d t d th i f● Collect already existing data and then examine forsoils and geological conditions

● Collect details required for economic designs

● Helps in deciding future programme of site● Helps in deciding future programme of site

investigations, scope of work, methods of

exploration to be adopted, types of samples to be

taken and the laboratory testing and in-situ testing.


taken and the laboratory testing and in situ testing.

5

Study of Maps● Study of maps from Survey of India or

Geological survey of India to get informationGeological survey of India to get informationregarding faults, folds, cracks, fissures, etc.


Folds


Faults


Aerial photography


Satellite imagesSatellite images


PRELIMINARY INVESTIGATIONS

● To determine the depth, thickness, extent anditi f h t t t th itcomposition of each stratum at the site.

● The depth of bed rock and the ground water● The depth of bed rock and the ground watertable is also determined.

● Generally in the form of test pits and few borings

● Tests are conducted with cone penetrometers● Tests are conducted with cone penetrometersand sounding rods to obtain information aboutthe strength and compressibility of soils.

Geoph sical methods are sed for locating the● Geophysical methods are used for locating theboundaries of different strata.


Detailed Investigations

Direct Method

Indirect methods

Semi-direct methods

(Borings)Trial PitsTrenches

Geophysical methodsSeismic Method

Auger BoringShell and Auger BoringWash Boring

Electrical Resistivity Method

Soundings or penetration testsWash BoringPercussion DrillingRotary Drilling

Soundings or penetration testsStandard Penetration Test (SPT)Static Cone Penetration Test (SCPT)D i C P t ti T t (DCPT)


Dynamic Cone Penetration Test (DCPT)

12

DIRECT METHODDIRECT METHOD

TEST PITS

● Usually made for supplementing other methods or for

minor structures

● Visual inspection of soil

● Personal feeling of soils

● Collection of soil samplesCo ec o o so sa p es


SEMI DIRECT METHODSSEMI DIRECT METHODS


AUGER BORING

● For soils with sides of the hole can remain unsupported

in dry statein dry state.

● Hand operated – 3 to 5 m depths

● Power driven – up to 50 m depth


HAND OPERATED AUGERS15

MACHINE OPERATED

AUGERS


SHELL AND AUGER BORING

● Shell used for soil with sides of

the hole cannot remainthe hole cannot remain

unsupported.

B i i l t t d fi t ith● Boring is always started first with

augering and the shell is used for

advancing the bore hole.

● Shell raised above the bottom of

the hole and allow it to fall freely.

The impact of the drop cuts thep p

soil and pushes the soil in to the

tube.tube.

● After filled, shell is withdrawn

and emptied


and emptied.

17

WASH BORING

● For soils which auger

boring is not suitableboring is not suitable

● For soils not mixed with

gravel and boulders

● For collecting samples● For collecting samples,

replace drill bit with

lsamplers

● Change of rate of

progress and change of

colour of wash watercolour of wash water

indicate change in soil

t t


strata18

PERCUSSION DRILLING

● Heavy drill bit suspended

from a drill rod or a cablefrom a drill rod or a cable

and is driven by repeated

blows

● Water is added to

facilitate the breaking of

stiff sol or rockstiff sol or rock

● Not suitable for loose

sand and is slow in

plastic claysp y


PERCUSSION DRILLINGDRILLING

TOOLS


ROTARY DRILLING● Fast in rocks

● Drill bit fixed to the lower end● Drill bit fixed to the lower end

of a drill rod is rotated by

power

● Bentonite slurry is forcedy

under pressure through the

drill rod and it comes up alongdrill rod and it comes up along

the cutting soil

● Rock cores can be obtained by

using suitable diamond drillg

bits and core barrels


ROTARY DRILLING


DEPTH OF EXPLORATION

● Governed by the depth of the

influence zone which dependsinfluence zone which depends

on the type of structure,

intensity of loading shape andintensity of loading, shape and

disposition of the loaded area,

th il fil d th h i lthe soil profile and the physical

characteristics of the soil.

● The depth upto which the

stress increment due to

superimposed loads can

produce significant settlementp g

and shear stress is known as

the “Significant Depth”. PRESSURE BULB


g p PRESSURE BULB

23

GUIDELINES FOR DEPTH OF EXPLORATIONSl. No. TYPE OF FOUNDATION DEPTH OF EXPLORATION

(i) Isolated Spread Footing or Raft 1.5 B( ) g

(ii) Adjacent Footings with clear spacing < 2B 1.5 L


ADJACENT ROWS OF FOOTINGSSl.No.

TYPE OF FOUNDATION DEPTH OF EXPLORATION

(iii) Adjacent Rows of Footings with clear spacing < 2B 4 5 B(iii) Adjacent Rows of Footings with clear spacing < 2B 4.5 B

Adjacent Rows of Footings with clear spacing > 2B, but < 4B 3 B

Adjacent Rows of Footings with clear spacing P 4B 1 5 BAdjacent Rows of Footings with clear spacing P 4B 1.5 B


PILE AND WELL FOUNDATIONSSl. No. TYPE OF FOUNDATION DEPTH OF EXPLORATION

(iv) Pile and Well Foundation 1.5 x Width of Structure from the bearing ( ) glevel (Toe of pile or bottom of well)


ROAD CUTS

Sl. No. TYPE OF FOUNDATION DEPTH OF EXPLORATION

(v) Road Cuts Bottom width of the cut (B)


FILLS

Sl. No. TYPE OF FOUNDATION

DEPTH OF EXPLORATIONFOUNDATION

(vi) Fills 2 m below GL or height of fill (H) whichever is greater


SOWERS AND SOWERS (1970) FORMULA

● Empirical Relationship for Multistoreyed Buildings

( ) 7.0SCD =where

D = Depth of exploration

C = Constant

= 3 for Light steel buildings & Narrow concrete bldgs

6 for Hea Steel bldgs & Wide Concrete bldgs= 6 for Heavy Steel bldgs & Wide Concrete bldgs.

S = No. of storeys


Spacing of Borings

● The number and spacing of bore holes or trial pits willdepend upon the extent of the site and nature ofdepend upon the extent of the site and nature ofstructures coming on it.

● For a compact building site covering an area of about0.4 hectre, one bore hole or trial pit in each corner andone in the centre.

● For smaller buildings one bore hole or trial pit in the● For smaller buildings, one bore hole or trial pit in thecentre.


Sl. No. Nature of project Spacing

1. Highways 300 to 600 m

2. Earth dams 30 to 60 m

3. Borrow pits 30 to 120 m3 o o p s 30 o 0

4 Multi-storey buildings 15 to 30 m4. Multi storey buildings 15 to 30 m

5 Single storey factories 30 to 90 m5. Single storey factories 30 to 90 m.


SAMPLES● DISTURBED SAMPLES

– REPRESENTATIVE SAMPLES• GRAIN SIZE ANALYSIS• ATTERBER LIMITS• SPECIFIC GRAVITY• CHEMICAL ANALYSIS

NON REPRESENTATIVE SAMPLES– NON-REPRESENTATIVE SAMPLES• Mixture of materials from various strata or some

mineral constituents lost● UNDISTURBED SAMPLES

• SHEAR STRENGTH PARAMETERS• CONSOLIDATION PARAMETERS• IN-SITU DENSITY AND WATER CONTENT• COEFFICIENT OF PERMEABILITY

BLOCK OR CHUNK SAMPLES


● BLOCK OR CHUNK SAMPLES32

SAMPLERS

● Based on Mode of operation

–Open Drive Samplers

• Thick wall type – Split Spoon Sampler (SPT

S l )Sampler)

• Thin wall type – Shelby Tube Sampler (UDSyp y p (

Sampler)

–Stationary Piston Sampler

–Rotary Sampler


SPLIT SPOON SAMPLER


THIN WALLED SAMPLER


SEALING METHODS


PISTON SAMPLER


OSTERBERG PISTON SAMPLER


ROTARY SAMPLER


BLOCK OR CHUNK SAMPLES


SAMPLER PARAMETERS

● Inside Clearance (CI)

– Should be between 1 to 3 %

All f l ti i f– Allows for elastic expansion of

the soil as it enters the tube,

reduces frictional drag on thereduces frictional drag on the

sample from the wall of the tube.

● Outside Clearance (Co)

– The outside clearance should not

be much greater than the inside

clearance.

– This facilitates the withdrawal of


the sampler from the ground.41

SAMPLER PARAMETERS

● Area Ratio (Ar)

− Should be kept as low as possible.

− ≤ 20% for stiff formations and ≤10% for soft sensitive clays.


University Questions

● Comment on the area ratios of the following samples:

Outer Dia (mm) Inner Dia (mm)Outer Dia (mm) Inner Dia (mm)

(i) Split spoon sampler 50 25

(ii) Drive tube 100 90

(iii) Shelby tube 50 47

Solution :

Outer Dia

(mm)

Inner Dia

(mm)

Area Ratio

(mm) (mm)

(i) Split spoon sampler 50 25 300 %

(ii) Drive tube 100 90 23.46 %

(iii) Sh lb t b 50 47 13 17 %


(iii) Shelby tube 50 47 13.17 %

43

Rock Coring Parameters

LengthR nCoreTotal

recovered core theofLength Recovery Core =

LengthRun CoreTotal


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GEOTECHNICAL ENGINEERING II (ModuleI PartII – 1)