In. Situ Soil Test

U.E.Tl Pavement & Foundation

M.Safdar, 2007-civil-48 Page 1

FIELD STRENGTH TESTS

The following are the major field tests for determining the soil strength.

Vane shear test (VST)

Standard Penetration Test

(SPT)

Cone Penetration Test

(CPT)

The Borehole Shear Test (BST)

The Plate Load Test (PLT).

The Flat Dilatometer Test

(DMT)

The Pressure-meter Test

(PMT)



1. Standard Penetration test (SPT Test, ASTM D 1586)

The test was developed in 1927 and standardized by ASTM in 1958. This test has been used

extensively in USA, UK and Pakistan for estimating relative density and angle of internal friction

of coarse grained soil, granular soil especially sands, silty sands etc. This method describes the

standard penetration test using the split-barrel sampler to obtain the resistance of soil to

penetration (N-value), using a 63.5 kg hammer falling .76m and to obtain representative

samples for identification and laboratory tests.

The method is applicable to all soil types. It is most often used in granular materials but also in other materials when simple in-place bearing strengths are required. It is also used when samples cannot easily be recovered by other means . The Standard Penetration Tests aims to determine the SPT N value, which gives an indication of the soil stiffness and can be empirically related to many engineering properties.

Setup & Working Principle:

I. In this test a standard spoon sampler ( also known as split barrel) of about 500mm outer

diameter is driven into the ground by a hammer weighing about 63.4kg (140lb) and

falling a distance of 0.76m (30 inch).

II. The sample is driven 0.15m (6 inch) into the soil at testing depth (i -e bottom of hole)

and the number of blows (N) required to derive it a further 0.3m (12inch) is then

recorded. N in general is known as the SPT resistance of the soil.



The boring log shows refusal and the test id halted if

a) 50 blows are required for any 150mm increment.

b) 100 blows are obtained (to derive the required 300m).

c) 10 successive blows produce no advance.

Test Data & Soil Properties obtained from the test:

Only one parameter is obtained fro the test i-e SPT N value (no of blows for 1ft penetration)

The following soil properties can be estimated.

Unit Weight (γ)

Relative Density (Dr)

Angle of internal

friction (φ)

undrained Compressive Strength (qu)

Bearing Capacity of Foundation

Stress Strain Modulus (Es)



Advantages:

Quick & simple to Perform

Equipment & expertise are easily available

Can penetrate into dense layers, gravel and fills

Provide a representative sample

Disadvantage:

Does not provide continuous data (5ft interval)

Limited applicability to cohesive soil, gravels, boulders, cobbles

A number of correlation are applied in order to get standard value



2. Cone Penetration Test (CPT, ASTM D3441)

The mechanical cone penetrometer probe, invented in The Netherlands in 1932 by P.

Barentsen, measures the quasi-static thrust required to push a solid, conical tip having a 60

degree apex angle and a cross-sectional area of 10 cm2 into the foundation soil. The

operator advances the cone using a nested, dual rod system, the outer rods providing

strength to penetrate the cone in a collapsed configuration, and the inner rods allowing him

or her to advance only the cone tip at each test depth (generally at 20-cm intervals) while

measuring the hydraulic thrust pressure at the top of the rods. In 1953, Begemann

modified the probe to include a friction sleeve just behind the tip. For the friction cone test,

the inner rods initially advance only the tip for a short distance, and then engage both the

tip and a friction sleeve together. The center of the friction sleeve is located 20 cm above

the tip, and the value of unit soil adhesion acting on it is computed by subtracting the tip-

only thrust force (from the previous test depth) and dividing by the sleeve area of 150

cm2. The engineer then divides the unit tip bearing from the previous test depth by the unit

adhesion to determine the friction ratio (both readings then apply to the same depth), and

uses an empirical chart to identify the type of soil. Depth plots of unit bearing and friction

ratio also provide a relative profile of the site stratigraphy.


The test is performed using a cylindrical penetrometer with a conical tip (cone) penetrating the

ground at a constant rate. During the penetration, the forces on the cone and the friction sleeve are measured. The measurements are carried out using electronic transfer and data logging, with a measurement frequency that can secure detailed information about the soil conditions. Figure 3 shows an electrical friction cone with cut-away friction sleeve.



Cone Penetration Tests are conducted to obtain the cone resistance, the side friction and, if there is a piezocone, the pore pressure. The soil type can be determined by

analysing these results, the values can also be used in the design of shallow foundations through the estimation of stiffness and shear strength of cohesive soils.

A 60o cone with face area 10cm2 and 150cm2 'friction sleeve' is hydraulically pushed into the ground at a constant speed (ranging form 1.5 to 2.5 cm/s). The force required to

maintain this penetration rate, and the shear force acting on the friction sleeve are recorded. The friction ratio (cone resistance / side friction) gives an indication of the soil

type.

This test is suitable for soft clays, soft silts and fin to medium sand deposits.

Test data & soil properties obtained from the test:

Following parameters are obtained from the test

CONE RESISTANCE QC = FC / AC

SIDE FRICTION FS = FS / AS



Friction Ratio Rf = fs / qc

Where Fc = pushing force, Ac = cone plan area, Fs = shear force on friction sleeve, As = area of friction sleeve.

From these parameters following properties of soil can be determined.

Statrification Soil Type Soil densityIn situ stress

Condition

Shear Strength Parameter

(C,φ)

Over Consoildation

ratio

Bearing Capacity (to design pile)



Advantages:

The test can be performed on wide range of soil type.

It provide continuous or near continuous data Provides accurate parameters for P-y analyses for lateral loads on deep foundations

Determine accurate values for strength or compressibility of the soil strata

Disadvantage:

The test does not provide any soil sample

It can not penetrate into very dense soil containing boulder & cobbles.

3. The Flat Dilatometer Test (DMT ASTM D 6635)

In 1975, Dr. Silvano Marchetti invented the Flat Dilatometer, consisting of sharpened

blade with a circular membrane located on one side, to investigate H-pile behavior for lateral loads.


The dilatometer consists of a steel blade having a thin, expandable, circular steel membrane mounted on one face. When at rest, the membrane is flush with the surrounding flat surface of the blade. The blade is connected, by an electro-pneumatic tube running through the insertion rods, to a control unit on the surface. The control unit is equipped with pressure gauges, an audio-visual signal, a valve for regulating gas flow (provided by a tank) and vent valves. The blade is advanced into the ground using common field equipment, i.e. push rigs normally used for the cone penetration test (CPT) or drill rigs (The DMT can also be driven, e.g. using the SPT hammer and rods, but statically push is by far preferable). Pushing the blade with a 20 ton Penetrometer truck is most effective (up to 100 m of profile per day).



The test starts by inserting the dilatometer into the ground. Soon after penetration, the operator inflates the membrane and takes, in about 1 min, two readings: the A pressure, required to just begin to move the membrane ("lift-off"), and the B pressure, required to move

the center of the membrane 1.1mm against the soil. A third reading C ("closing pressure") can also optionally be taken by slowly deflating the membrane soon after B is reached. The blade is

then advanced into the ground of one depth increment (typically 20 cm). The DMT can test from extremely soft to very stiff soils (clays with cu from 2 - 4 to 1000 kPa, moduli M from 0.5

to 400 MPa).


The data is obtained in the form of a graph i-e pressure vs penetration. From this graph following pressures are determined to calculate three parameter of the test which will be used to determine the soil properties.

PB = Lift off pressure

PE = Pressure to yield the soil

P1.1 = Pressure require for 1.1mm of piston movement



Following parameters can be calculated from these pressure.

The soil properties obtained from the test are

Advantages:

Settlement prediction has been considered ore reliable than any other test

DMT can evaluate the OCR & Ko of any type of soil

Horizontal coefficient of consolidation & horizontal permeability can be determined

Can identify the active or old slip surfaces in clay slopes using kd profile of DMT

Dilatometetr Modululs (Ed)

Lateral Stress Index (Kd)

Material Index (Id)

Tangent vertical constrained modulus [M]

Undrained shear strength for clays

[cu]

Drained friction angle for sands [Φ]

Total unit weight of soil [γt]

Preconsolidation pressure [pc]

Over consolidation ratio [OCR]

Coefficient of lateral earth

pressure at rest [ko]



Determine accurate values for strength or compressibility of the soil strata Provides accurate parameters for P-y analyses for lateral loads on deep foundations Accurately measures the low strain shear wave velocity using the true interval method Accurately evaluates ground improvement by performing before and after DMT

Disadvantage:

No sample is recovered

Blade penetration effects the strength & stiffness

Result of DMT are affected if the blade drifts out vertical during penetration

Operator should have skills

Not cheap test

4. Pressure meter Test (PMT ASTM D4719 - 07)

The pressuremeter test is an in-situ testing method which is commonly used to achieve a quick

and easy measure of the in-situ stress-strain relationship of the soil which provides parameters

such as the elastic modulus.


The pressuremeter test is an in-situ testing method used to achieve a quick measure of the in-

situ stress-strain relationship of the soil. In principle, the pressuremeter test is performed by

applying pressure to the sidewalls of a borehole and observing the corresponding deformation.

The pressuremeter consists of two parts, the read-out unit which rests on the ground surface,

and the probe that is inserted into the borehole (ground). The original Ménard-type

pressuremeter was designed to be lowered into a performed hole and to apply uniform

pressure to the borehole walls by means of inflatable flexible membrane. As the pressure

increases, the borehole walls deform. The pressure is held constant for a given period and the

increase in volume required for maintaining the constant pressure is recorded. A load

deformation diagram and soil characteristics can be deduced by measurement of the applied

pressure and change in the volume of the expanding membrane.



The major difference between categories of pressuremeter lies in the method f installation of

the instrument into the ground. Three main types of pressuremeters are:

The borehole pressuremeter: The instrument is inserted into a performed hole. The self-boring pressuremeter: The instrument is self-bored into the ground with the

purpose of minimizing the sol disturbance caused by insertion. Displacement pressuremeters: The instrument is pushed into the ground from base of a

borehole. The soil displaced by the probe during insertion enters the body of instrument, reducing the disturbance to the surrounding soil (see Cone-pressuremeter).

There are different approaches the interpretation of results and the determination of material

properties from pressuremeter tests. In general, these approaches rely either on empirical

correlations to allow measured co-ordinates of pressure and displacement to be inserted

directly into design equations, or on solving the boundary problem posed by the pressuremeter

test.

http://www.geotechdata.info/geotest/insitu/pressuremeter/cone-pressuremeter




The data is obtained in the form of a graph i-e pressure vs expansion. From this graph following

pressures are determined to calculate three parameter of the test which will be used to determine the soil properties.

PB = Lift off pressure

PE = Pressure to yield the soil

Pl = Limit Pressure

The soil properties obtained from the test are

Advantages:

Allows assessment of insitu horizontal stress Well condition boundary condition Allows direct measurement of shear stiffness & undrained shear strength

Can be conveniently used with drilling equipment or pushed in with direct push equipment.

While tests can be done in soft clay or loose sands, the test is best used in dense sands, hard clays and weathered rock which cannot be tested with push equipment.

An extensive database of load test results allows the geotechnical engineer to accurately

design for shallow foundations and for lateral and vertical capacity of deep foundations.

Pressuremeter Elastic Modulus

Horizontal lateral earth pressure at

restReload Modulus

Total unit weight of soil [γt]

Preconsolidation pressure [pc]

Over consolidation ratio [OCR]

Coefficient of lateral earth

pressur at rest [ko]



Disadvantage:

No sample is recovered

Appreciable data processing is required

Operator needed to be skilled skills

Not cheap test

References:

I. FOUNDATION ANALYSIS AND DESIGN BY JOSEPH E. BOWLES

II. FUNDAMENTALS OF SOIL MECHANICS BY M. SIDDIQUE & AZIZ AKBAR

III. http://www.authorstream.com/Presentation/rizwankhurram-

508310-field-tests-soil-parameters/

IV. http://www.conepenetration.com/online-book/cf-cone/cf-cone-

cone-penetration-test/

V. http://civcal.media.hku.hk/airport/investigation/fieldwork/cpt/defau

lt.htm

VI. http://www.insitusoil.com/dilatometer.html

VII. http://www.geotechdata.info/geotest/pressuremeter-test

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In. Situ Soil Test