Insitu and lab tests

Topic Of Presentation
INSITU TESTS & LAB TESTS

Insitu Tests
Insitu tests are performed on a rock or a soil at a place where they are.
Or
Tests Performed with in a borehole.
Names Of Insitu tests are:
• Cone penetration test
• Standard Penetration Test
• Direct Shear Test
• Plate Load Test

Lab Tests
Different techniques used in a lab for investigation of a sample.
Lab Tests Are:
• Uniaxial compressional Test (UCS)
• Atterberg Limits
• Tri axial Shear Test

Introduction
This is the method of conducting the load test on soils and evaluation of
bearing capacities and settlement from this test. This method assumes
that down to the depth of influence of stresses the soil strata is
reasonably uniform. This should be verified by boring or sounding.

Apparatus
The apparatus consists of:
• Bearing Plates:
• Loading equipment
• Settlement measurements

Bearing Plates
Bearing Plates consist of a mild steel 75 cm in diameter and 1.5 to 2.5
cm thickness, and few other plates of same thickness, but smaller
diameters (usually 60, 30 and 22.5 cm dia ) used as stiffeners.

Loading Equipment
Loading equipment consist of a reaction or dead load and a hydraulic
jack. The reaction frame may suitable be loaded to give the needed
reaction load on the plate.

Settlement Measurements
Settlement measurements may be made by means of three or four dial
gauges fixed on the periphery of the bearing plate from an independent
datum frame. The datum frame should be supported far from the
loaded area.

Procedure
• The test side is prepared and lose material is removed so that 75 cm
diameter plate rest horizontally in full contact with the soil sub-grade.
• The top soil may be removed to a depth of about 20 cm before
testing.
• The plate is seated accurately and then a seating load equivalent to a
pressure of 0.07kg/cm² is applied and released.
• A load is applied of mean of jack to cause average settlement.
• Average of 3 or 4 settlement dial reading is taken to the applied load.
• The procedure is repeated till the settlement is about 1.75 mm or
more.

Calculations:
Point load strength index (Is) = (P*1000)/D2 Mpa
-Where P is breaking load in kN
-D is the distance between plates in mm
Corresponding point load strength index for the standard core size of 50
mm (Is50) diameter is given by the following equation:
Is50 = (P*1000)/(D1.5√50) MPa

Limitations
• The width of test plate should not be less then 30cm.
• The settlement influence zoon is much larger for the real foundation
size then that for test plates.
• The foundation settlements in loose sands are usually much larger
then what is predicted by plate load test.
• Plate load test is relatively short duration test and give mostly the
immediate settlements.
• In case of granular soils the immediate is close to total settlements.

Topic:
Direct Shear Test (DST)

Direct Shear Test
• A direct shear test is a laboratory or field test used by geotechnical
engineers to measure the shear strength properties of soil or rock
material, or of discontinuities in soil or rock masses.
• The U.S. and U.K. standards defining how the test should be
performed are ASTM(American Society for Testing and Materials) D
3080, AASHTO(American Association of State Highway and
Transportation Officials) T236 etc. For rock the test is generally
restricted to rock with (very) low shear strength. The test is, however,
standard practice to establish the shear strength properties of
discontinuities in rock.

Purpose:
• This test is performed to determine the consolidated-drained shear
strength of a sandy to silty soil.
• The shear strength is one of the most important engineering
properties of a soil, because it is required whenever a structure is
dependent on the soil’s shearing resistance.
• The shear strength is needed for engineering situations such as
determining the stability of slopes or cuts, finding the bearing
capacity for foundations, and calculating the pressure exerted by a
soil on a retaining wall.

Procedure:
• The test is performed on three or four specimens from a relatively undisturbed soil
sample.
• A specimen is placed in a shear box which has two stacked rings to hold the
sample; the contact between the two rings is at approximately the mid-height of
the sample.
• A confining stress is applied vertically to the specimen, and the upper ring is pulled
laterally until the sample fails, or through a specified strain.
• The load applied and the strain induced is recorded at frequent intervals to
determine a stress–strain curve for each confining stress.
• Several specimens are tested at varying confining stresses to determine the shear
strength parameters, the soil cohesion (c) and the angle of internal friction,
commonly known as friction angle.
• The results of the tests on each specimen are plotted on a graph with the peak (or
residual) stress on the y-axis and the confining stress on the x-axis. The y-intercept
of the curve which fits the test results is the cohesion, and the slope of the line or
curve is the friction angle.

Computation
The strength of a soil depends of its resistance to shearing stresses. It is made up of basically the
components;
1. Frictional – due to friction between individual particles.
2. Cohesive - due to adhesion between the soil particles.
Equation:
τf = c + σf tan ø
Where τf = shearing resistance of soil at failure
c = apparent cohesion of soil
σf = total normal stress on failure plane
ø = angle of shearing resistance of soil (angle of internal friction)
This equation can also be written in terms of effective stresses:
Where c’ = apparent cohesion of soil in terms of effective stresses
σ'f = effective normal stress on failure plane
ø’ = angle of shearing resistance of soil in terms of effective stresses
σ'f = σf - uf
uf = pore water pressure on failure plane
τf = c’ + σ’f tan ø’

Conditions:
Direct shear tests can be performed under several conditions:
• The sample is normally saturated before the test is run, but can be run at the in-
situ moisture content.
• The rate of strain can be varied to create a test of undrained or drained conditions,
depending whether the strain is applied slowly enough for water in the sample to
prevent pore-water pressure buildup.

Advantages Of DST:
• The advantages of the direct shear test over other shear tests are the
simplicity of setup and equipment used, and the ability to test under
differing saturation, drainage, and consolidation conditions.

Triaxial Shear Test
Triaxial shear test is a common method to measure the mechanical
properties of many deformable solids, especially soil (e.g., sand, clay)
and rock, and other granular materials or powders. There are several
variations on the test.

Procedure
• In a triaxial shear test, stress is applied to a sample of the material being tested in a
way which results in stresses along one axis being different from the stresses in
perpendicular directions.
• This is typically achieved by placing the sample between two parallel platens which
apply stress in one ) direction, and applying fluid pressure to the specimen to apply
stress in the perpendicular directions.
• The application of different compressive stresses in the test apparatus causes shear
stress to develop in the sample; the loads can be increased and deflections
monitored until failure of the sample.
• During the test, the surrounding fluid is pressurized, and the stress on the platens is
increased until the material in the cylinder fails and forms sliding regions within
itself, known as shear bands.
• The geometry of the shearing in a triaxial test typically causes the sample to
become shorter while bulging out along the sides. The stress on the platen is then
reduced and the water pressure pushes the sides back in, causing the sample to
grow taller again. This cycle is usually repeated several times while collecting stress
and strain data about the sample.
• During the test the pore pressures of fluids (e.g., water, oil) or gasses in the sample
may be measured using Bishop's pore pressure apparatus.

Techniques Of A Test
• For Soil Sample:
For soil samples, the specimen is contained in a cylindrical latex sleeve with a flat,
circular metal plate or platen closing off the top and bottom ends. This cylinder is
placed into a bath of a hydraulic fluid to provide pressure along the sides of the
cylinder. The top platen can then be mechanically driven up or down along the axis of
the cylinder to squeeze the material. The distance that the upper platen travels is
measured as a function of the force required to move it, as the pressure of the
surrounding water is carefully controlled. The net change in volume of the material can
also be measured by how much water moves in or out of the surrounding bath, but is
typically measured - when the sample is saturated with water - by measuring the
amount of water that flows into or out of the sample's pores.
• For Rock:
For testing of high-strength rock, the sleeve may be a thin metal sheeting rather than
latex. Triaxial testing on strong rock is fairly seldom done because the high forces and
pressures required to break a rock sample require costly and cumbersome testing
equipment.

Results
• From the triaxial test data, it is possible to extract fundamental
material parameters about the sample, including its angle of shearing
resistance, apparent cohesion, and dilatancy angle. These parameters
are then used in computer models to predict how the material will
behave in a larger-scale engineering application.
• An example would be to predict the stability of the soil on a slope,
whether the slope will collapse or whether the soil will support the
shear stresses of the slope and remain in place.
• Triaxial tests are used along with other tests to make such
engineering predictions.

What is Point Load Test?
• The compressive strength is the capacity of a material to withstand loads
tending to reduce size.
• It can be measured by plotting applied force against deformation in a
testing machine.
• Some materials fracture at their compressive strength limit; others deform
irreversibly, so a given amount of deformation may be considered as the
limit for compressive load.
• It is also called Uniaxial Compressive Strength.

Procedure:
• Specimens from drill cores are prepared by cutting them to
the specified length and are thereafter grinded and
measured. There are high requirements on the flatness of
the end surfaces in order to obtain an even load
distribution.
• Recommended ratio of height : diameter of the specimens is
2 : 3.
• The specimens are loaded axially up to failure or any other
prescribed level whereby the specimen is deformed and the
axial and the radial deformation can be measured using a
special equipment.

Topic:
Atterberg Limits of Soil

Atterberg
• Albert Atterberg was a Swedish chemist and agricultural scientist.
• Conducted studies to identify the specific minerals that give a clayey soil its plastic
nature
• Stated that depending on the water content, soil may appear in four states:
 Solid (no water)
 semi-solid (brittle, some water)
 plastic (moldable)
 liquid (fluid)
• In each state the consistency and behavior of a soil is different and thus so are its
engineering properties.
• The boundary between each state can be defined based on a change in the soil's
behavior.

Plastic limit
• The plastic limit (PL) is the water content (w%) where soil starts to
exhibit plastic behavior.

Liquid limit
• The liquid limit (LL) is the water content where a soil changes from
liquid to plastic behavior.
• Determined using a Casagrande cup (lab) or cone penetrometer
(field).

Shrinkage limit
• The shrinkage limit (SL) is the water content where further loss of
moisture will not result in any more volume reduction
• The shrinkage limit is much less commonly used than the liquid limit
and the plastic limit.

Use of Plasticity Index
• The PI is the difference between the liquid limit and the plastic limit
• (PI = LL-PL).
• The plasticity index is the size of the range of water contents where
the soil exhibits plastic properties.
Meaning:
• High PI tend to be clay
• Low PI tend to be silt
• PI of 0 tend to have little or no silt or clay.

Use of Liquid & Plastic Limits
Used internationally for soil identification and soil classification
(AASHTO).

Abdul Hafeez Khawaja
Roll # 23

Topic:
Standard Penetration Test
(SPT)

Standard Penetration Test (SPT)
• The standard penetration test (SPT) is an in-situ dynamic penetration
test designed to provide information on the geotechnical engineering
properties of soil. The test procedure is described in ISO 22476-3,
ASTM D1586 and Australian Standards AS 1289.6.3.1.

Procedure
• The test uses a thick-walled sample tube, with an outside diameter of
50.8 mm and an inside diameter of 35 mm, and a length of around
650 mm.
• This is driven into the ground at the bottom of a borehole by blows
from a slide hammer with a mass of 63.5 kg (140 lb) falling through a
distance of 760 mm (30 in).
• The sample tube is driven 150 mm into the ground and then the
number of blows needed for the tube to penetrate each 150 mm (6
in) up to a depth of 450 mm (18 in) is recorded. The sum of the
number of blows required for the second and third 6 in. of
penetration is termed the "standard penetration resistance" or the
"N-value".
• In cases where 50 blows are insufficient to advance it through a 150
mm (6 in) interval the penetration after 50 blows is recorded.
• The blow count provides an indication of the density of the ground,
and it is used in many empirical geotechnical engineering formulae.

Purpose
• The main purpose of the test is to provide an indication of the relative density of granular
deposits, such as sands and gravels from which it is virtually impossible to obtain undisturbed
samples.
• The great merit of the test, and the main reason for its widespread use is that it is simple and
inexpensive.
• The soil strength parameters which can be inferred are approximate, but may give a useful guide
in ground conditions where it may not be possible to obtain borehole samples of adequate quality
like gravels, sands, silts, clay containing sand or gravel and weak rock.
• In conditions where the quality of the undisturbed sample is suspect, e.g., very silty or very sandy
clays, or hard clays, it is often advantageous to alternate the sampling with standard penetration
tests to check the strength.
• If the samples are found to be unacceptably disturbed, it may be necessary to use a different
method for measuring strength like the plate test.
• When the test is carried out in granular soils below groundwater level, the soil may become
loosened. In certain circumstances, it can be useful to continue driving the sampler beyond the
distance specified, adding further drilling rods as necessary.
• The usefulness of SPT results depends on the soil type, with fine-grained sands giving the most
useful results, with coarser sands and silty sands giving reasonably useful results, and clays and
gravelly soils yielding results which may be very poorly representative of the true soil conditions.
Soils in arid areas, such as the Western United States, may exhibit natural cementation. This
condition will often increase the standard penetration value.

Correlation With Soil Mechanical
Properties
• Despite its many flaws, it is usual practice to correlate SPT results
with soil properties relevant for geotechnical engineering design.
• SPT results are in-situ field measurements, and not as subject to
sample disturbance, and are often the only test results available,
therefore the use of correlations has become common practice in
many countries.

Reasons:
• The results are limited to whole numbers for a specific driving
interval, but with very low blow counts, the granularity of the results,
and the possibility of a zero result, makes handling the data
cumbersome (difficult to use).
• In loose sands and very soft clays, the act of driving the sampler will
significantly disturb the soil, including by soil liquefaction of loose
sands, giving results based on the disturbed soil properties rather
than the intact soil properties.

Problems With SPT
(Limitations)
• The Standard Penetration Test recovers a highly disturbed sample,
which is generally not suitable for tests which measure properties of
the in-situ soil structure, such as density, strength, and consolidation
characteristics.
• This results in blow counts which are not easily converted to SPT N-
values - many conversions have been proposed, some of which
depend on the type of soil sampled, making reliance on blow counts
with non-standard samplers problematic.

References
Bishop, A. W. (find reference on large direct shear tests.
Converse, F. J. (1952), "The Use of the Direct Shear Testing Machine in
Foundation Engineering Practice," Symposium on Direct Shear Testing of Soils,
ASTM, Vol. 131, pp. 75-80.
Japanese Industrial Standard. 1993. JIS A1107: Method of Sampling and Testing
for Compressive Strength of Drilled Cores of Concrete.
Ruijie L.K. 1996. The Diameter-Compression Test for Small Diameter Cores.
Journal of Materials and Structures. 29(1): 56-59.
"Materials Engineering." Main_page [SubsTech]. N.p., n.d. Web. 22 Sept. 2013.
AMS Materials Data sheets, www.matweb.com
www.google.com
www.googleimages.com
www.geotech.com
www.cyut.edu.tw

Insitu and lab tests

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