Geotechnical & Foundation Engineering Lab...

Geotechnical & Foundation Engineering Lab Manual

Geotechnical & Foundation Engineering Lab Manual

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Department of Civil EngineeringThe University of LahoreTABLE OF CONTENTS

EXPERIMENT NO. 1……………………………………………………………………………………………………………………………………………03CALIBRATION OF SPEEDY MOISTURE METER………………………………………………………………………………………………………….03EXPERIMENT NO. 207PERFORMANCE OF RELATIVE DENSITY TEST ON GRANULAR SOILS07EXPERIMENT NO. 310DETERMINATION OF SHEAR STRENGTH PARAMEERS OF SOIL BY DIRECT SHEAR APPARATUS10EXPERIMENT NO. 4………………………………………………………………………………………………………………………………………………..16DETERMINATION OF UNCONFINED COMPRESSIVE STRENGTH OF COHESIVE SOILS16EXPERIMENT NO. 521DETERMINATION OF UNCONFINED COMPRESSIVE STRENGTH OF COHESIVE SOILS WITH CEMENT……………………………. STABILIZATION……........................................................................................................................................................21EXPERIMENT NO. 625DETERMINATION OF CALIFORNIA BEARING RATIO OF LABORATORY COMPACTED SOILS25EXPERIMENT NO. 730PERFORMANCE OF CONSOLIDATION TEST ON COHESIVE SOILS USING ODEOMETER30EXPERIMENT NO. 8………………………………………………………………………………………………………………………………………………..38PERFORMANCE OF STANDARD PENETRATION TEST ………………………………………………..…………………………………………….38EXPERIMENT NO. 944PERFORMANCE OF TRI-AXIAL COMPRESSION TEST ON COHESIVE SOILS UNDER UN-CONSOLIDATED………………………..UN-DRAINED CONDITION44EXPERIMENT NO. 1050PERFORMANCE OF TRI-AXIAL COMPRESSION TEST ON COHESIVE SOILS UNDER CONSOLIDATED……………………………….UN-DRAINED CONDITION……………………………………………………………………………………………………………………………………….50EXPERIMENT NO. 1154DETERMINATION OF COEFFICIENT OF PERMEABILITY BY CONSTANT HEAD APPARATUS54EXPERIMENT NO. 1259DETERMINATION OF COEFFICIENT OF PERMEABILITY BY FALLING HEAD APPARATUSError! Bookmark not defined.

APPENDIX 62(RELEVANT ASTM STANDARDS)

Experiment#1

Calibration of Speedy Moisture Meter

Speedy moisture meter:

Speedy moisture meter is a portable system for measuring the moisture content of a wide range of materials including soils, aggregates, dust and powders (and liquids). The system consists of a low pressure vessel fitted with a pressure gauge and an electronic scale and test accessories.

Mechanism:

Moisture measurements are made by mixing a weighed sample of the material with a calcium carbide reagent in the sealed pressure vessel. The reagent reacts chemically with water in the sample, producing acetylene gas that in turn increases the pressure within the vessel. The pressure increase in the vessel is proportional to the amount of water in the sample, the moisture content can be read directly from the calibrated pressure gauge.

Features and Advantages:

When compared with other moisture measurement systems, the Speedy moister is often the most practical solution, especially when working in the field.

• Simple to use

• Robust and reliable

• Portable and requires no external power source

• Versatile - many materials can be measured over a wide range

OBJECTIVE:

a) To compare the moisture contents obtained from oven drying method with the moisture contents determined by speedy moisture meter.

b) To develop a relationship between moisture contents obtained from oven drying technique and speedy moisture meter.

THEORY

Moisture Content (w)

It is defined as the ratio of the weight of water in a given volume of soil to the weight of the solid particles in that same volume.

w=

Where,

Ww = Weight of soil water in grams

Ws = Weight of soil in grams (oven dried weight of soil)

APPARATUS:

· Speedy moisture meter

· Two 1.25in steel balls

· Cleaning brush and cloth

· Scoop for measuring calcium carbide reagent

· Calcium carbide reagent

· Container

· Oven with accurate temperature

PROCEDURE

1. Prepare three samples at three different moisture levels and place some amount from these samples in oven to determine their moisture contents by oven dry method.

2. Weight 26 gm of soil from each sample and place it in the cap of the tester.

3. Place the steel balls into the body and three scopes of Calcium carbide CaC2.

4. Place the sample in the cover of the “Speedy”. Hold the “Speedy” in a horizontal position and place the cover on the end. Bring the stirrup in position and tighten. This should be completed without the sample and reagent coming in contact with each other.

5. Hold vertically so that the material in the cap falls into the “Speedy” body.Return the instrument to a horizontal position, shake to break all lumps, and mix the soil and reagent. Rotate for 10 seconds, rest for 20 seconds. The rest time allows for dissipation of the heat generated by the chemical reaction. Continue this cycle for a minimum of 3 minutes.

6. When the needle stops moving, read the dial while holding the instrument in a horizontal position at an eye level.

7. Record the dial reading.

8. Thoroughly clean the tester with the brush provided.

W= (wsp/ (1-wsp))100

9. In second step find the moisture content by an oven dry method for the same soil specimens.

10. Take container (s) which had been marked with a specific number, and place some soil in the container and weigh it.

11. Placed the container (s) in the oven for 24 hours.

12. After 24 hours, weigh the container (s) find the weight of the water and the moisture content by applying the following formula:

W=%

At the end, plot the graph between moisture content obtained by speedy moisture and oven dry method.Develop a relationship between these two moisture contents.

OBSERVATIONS& CALCULATIONS:

Calibration Graph:

Draw a calibration graph between W (oven drying) and W (speedy moisture meter)

REFERENCE

ASTM D2216-98

Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass

ASTM D4944-04

Standard Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester

COMMENTS:

Experiment#2

Performance of Relative Density Test on Granular Soils

Relative density:

Relative density or density index is the ratio of the difference between the void ratios of a cohesionless soil in its loosest state and existing natural state to the difference between its void ratio in the loosest and densest states.

OBJECTIVE:

To find relative density of the granular soils by maximum and minimum void ratios.

THEORY:

This experiment is performed to determine the relative density of cohesionless, free draining soils using a vibrating table. The relative density of the soils is the ratio expressed as a percentage of the difference between maximum index void ratio and field void ratio of cohesionless free draining soil; to the differencebetween the maximum and minimum index void ratios.

or

Relative compaction = Rc =

Void Ratio: is the ratio between volumes of voids to the volume of soil solids. It is denoted by ‘e’.

emax: is the void ratio corresponding to the loosest density (γ d min) of soil.

emin: is the void ratio corresponding to the maximum density (γ d max) soil.

ef: is the void ratio corresponding to field density (γ d f) of soil.

=

e = – 1

Apparatus:-

· Mould of different sizes.

· Funds of different tube dia.

· Wt 25kg to apply surcharge pressure.

· Vibrating table in form of machine.

· Measuring Tape.

· Dial Gauge.

· Cutting Plate.

· Spatula.

PROCEDURE:

•Take soil sample in loosest state of cohesion les soil

•Check the max size of soil and then take the mould and placement device accordingly.

•Now take mould and placed it on vibratory table and fix it.

•With the help of funnel placed the soil into mould.

•With the help of spatula make surface of soil smooth and place plate on soil sample.

•Then put 25 kg weight on plate and then compacted whole instrument.

•Note the reading with the help of dial gauge. (Height of sample in loosest state)

•Now allow the vibrating table at 0.48mm of amplitude for 10 mins at 50 Hz in lab.

•After 10 mins we measure the height of compacted soil with the help of dial gauge.

•Measure all dimension of mould with the help of measuring tape.

•Weight the soil sample.

•Apply formula to calculate the value of emax ¬ and emin.

•For these values first we have to find rdmin and rdmax as we know that

γd min =

γd max =

Calculate e max and e min.

PRECAUTIONS:

· Funnel, through which the soil is to be placed, should be 0.5” to 1” above the soil surface and there should be no contact between the lower-end of the funnel with the soil surface.

· The vibrating table should be operated at specified frequency conforming to ASTM.

· This experiment is applicable for soils containing up to 15% fine particles (Passing #200) provided that the material is cohesion less and free draining.

· Maximum particle size for this experiment is 3”.

OBSERVATIONS& CALCULATIONS

REFERENCE

ASTM D4253

Standard Test Methods forMaximum Index Density and Unit Weight of Soils Using aVibratory Table

ASTM D4254

Standard Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density

COMMENTS:

Experiment#3

Determination of Shear Strength Parameters of Soil by Direct Shear Apparatus

OBJECTIVE

To perform direct shear test on granular soil in order to evaluate the shear strength parameters (c, φ).

THEORY:

Shear Strength: of a soil is a measure of its resistance to deformation by continuous displacement of its individual soil particles.

Soil shear strength is an important consideration in foundation bearing capacity analysis, highway and airfield design and construction, slope stability of earth embankments and retaining wall construction. The shear strength of a soil is derived from three basic components:

· Resistance to displacement because of interlocking of individual soil particles.

· Resistance to particle translation because of friction between individual soil particles at their common point of contact.

· Cohesion between the surfaces of the soil particles.

Which of these components or combination of components are actually effective in resisting shear deformation depends on whether the soil is cohesive or cohesion-less and on soil drainage and consolidation conditions before and after shearing process.

Cohesion-less Soil: is the one that possesses little or no attractive force between particles. Usually soils that classify as sand or gravel are considered to be cohesion-less.

Cohesive Soil: on the other hand, is usually fine grained soil containing greater percentages of clay particles. True cohesion can be developed between fine grained soil particles that have been in stationary contact over a long period of time.

The first hypothesis on soil shear strength was presented by coulomb. He hypothesized that the shear strength of soil was dependent on the two components i.e. cohesion and friction:

Where,

S = Shear strength

C = Cohesion

ф= Angle of internal friction

= Normal stress on the critical plane

Soil shear strength can be determined in the field; however it is most often accomplished in the laboratory using one of the common lab testing methods:

· Tri-axial Shear Test

· Unconfined Compression Test

· Direct Shear Test

APPARATUS:

· Direct shear machine with proving ring and appropriate dial gage

· Direct shear box

· Shear box cart

· Weighing Balance (L.C. ±0.01 gm)

· Horizontal dial gage (L.C. ±0.001 mm)

· Spatula

PROCEDURE:

· Assemble the shear strain assembly:

· Place the upper half of the shear box on the lower half.

· Place the two clamping screws in their proper holes to hold the two box halves in place.

· Turn the separation screws counter-clockwise until they no longer extend beyond the base of the upper shear box half.

· Place the assembled shear box in shear box cart making certain that it is pointed in the correct direction.

· Place the lower gripper plate (grid plate) in the shear box with the grippers extending upward.

· Preparation of soil sample:

· Carefully measure the dimensions of the shear box in preparation for calculating the specimen volume.

· If the dry density of the sample is known, then the weight of the specimen for one test can be computed.

· Prepare three soil samples with same dry density.

· Carefully place the soil specimen in the shear box until approximately one-third of the shear box volume is filled. Use a wooden or metal rod with a flat end to compact the soil to get the desired density. Repeat this filling and compacting operation two more times.

· Carefully place the upper gripper plate and loading cap on the leveled soil specimen.

· Place the shear box cart on direct shear machine.

· Place the loading ball on the loading cap and carefully lower the loading frame on its place.

· Apply the load by manually operating the machine until dial gage on the proving ring just begin to move. Immediately stop the machine and then back off slightly.

· Advance the separation screws in the upper shear box half clockwise until they just touch the lower half. Then advance each of them an additional amount to separate the shear box halves and create a shear plane.

· Carefully remove the clamping screws from the shear box.

· Set all the gages to zero.

· Start the horizontal loading and take the reading of load dial gage and horizontal shear displacement gage. Take the reading at an interval of 5 or 10 units of the horizontal dial displacement gage.

· Continue the test until the shear stress become essentially constant which is indicated by load dial gage or until a shear deformation of 10% of original dimension has been reached.

· When the failure had occurred reverse the applied load until the load cart can be removed.

· Remove the soil from the shear box.

· Repeat the test at least two more time with same dry density and different normal loads.

If the test is to be performed under saturated conditions the following alterations are suggested:

· Place porous stone at the bottom and top of the shear box along with gripper plate as mentioned in above steps.

· After placing the shear box cart in direct shear machine fill the cart completely with water and allow the sample to saturate for sufficient time.

PRECAUTIONS:

· The gripper vanes should be perpendicular to the direction of travel during shear.

· Apply the desired normal load by placing weights in the loading frame. Remember to include the weight of the loading frame as part of the normal load.

· Use a strain rate of 0.5 mm/min to the maximum of 2 mm/min.

OBSERVATIONS & CALCULATIONS

Lower box dimensions= mm mm Area=mm2

Least Count of Deformation dial gauge =mm/div

Proving ring constant =lbs/div

Horizontal Dial Gauge Reading

Load Dial Gauge Reading

Horizontal Displacement

Corrected Area

Horizontal Shear Force

Shear Stress

Normal Stress

Lb

KN

mm

m

mm2

m2

lb

KN

KPa

KPa

Col 1

Col 2

Col3=COL1*L.C

Col4=A-(b*Col3)

Col5=PRC*Col2

Col6 = Col5/Col4

Col7 = Col1/Col4

Graphs:

1. Graph between shear displacement and normal stress

2. Graph between shear stress and normal stress

RESULTS

The shear strength parameters are calculated from the equation obtained from the graph between shear stress and normal stress as:

Ʈ = mσ + c ………………….Eq.1

Where

Ʈ = Shear stress

σ = Applied normal stress

c = Cohesion

φ = Angle of internal friction obtained from slope (m) of Eq.1, i.e. φ = Tan-1 (m)

REFERENCE

ASTM D3080

Standard Test Method forDirect Shear Test of Soils Under Consolidated DrainedConditions

COMMENTS:

Experiment # 4

Determination of Unconfined Compressive Strength of Cohesive Soils

OBJECTIVE:

To perform unconfined compression test on cohesive soils to determine their unconfined compressive strength (qu) and undrained shear strength (su).

THEORY:

Unconfined Compressive Strength of Cohesive Soil:

Unconfined compressive strength of cohesive soil, qu, is defined as the load per unit area at which an unconfined cylindrical specimen of soil will fail in a simple compression test.

It is taken as the maximum load attained per unit area or the load per unit area at 15% axial strain, whichever is secured first during the performance of a test.

The unconfined compression test is perhaps the simplest, easiest and least expensive test for investigation of the shear strength of a cohesive soil. This test procedure is usually limited to cohesive soils, since there is no lateral support and the soil sample must be able to stand alone. A non-cohesive soil (such as sand) cannot generally stand alone in this manner without lateral support. The cohesion C is taken to be one-half the unconfined compressive strength (i.e., C = qu/2).

A cohesive soil gets most of its shear strength from its cohesion. Hence, for most cohesive soils, the cohesion (and therefore the shear strength) maybe estimated from the results of unconfined compression test. However, for soft and/or sensitive clay, the cohesion is commonly obtained instead from the results of field or laboratory vane tests.

This compression is based on the fact that the minor principal stress (Ʈ3 is zero) (atmospheric), and the angle of internal friction ø of the soil is assumed zero. To give the unconfined compression test more dignity, it is often called an “un-drained” or U test. With more knowledge concerning soil behavior available, it became evident that the unconfined compression test does not generally provide a very reliable value of soil shear strength for at least three reasons.

· The effect of lateral restraint provided by the surrounding soil mass on the sample is lost when the sample is removed from the ground. There is, however, some opinion that the soil moisture provides a surface tension (or confining) effect so that the sample is somewhat “confined”. This effect should be more pronounced if the sample is saturated or nearly so. This effect will depend on the relative humidity of the testing area, making a quantitative evaluation of it rather difficult.

· The internal soil conditions like degree of saturation, the pore water pressure under stress deformation and the effects of altering the degree of saturation) cannot be controlled.

· The friction on the ends of the sample from the loading platens provides a lateral restraint on the ends which alters the internal stresses by an unknown amount.

Errors from the first two factors cited above can be eliminated or at least reduced by using the confined (or tri-axial) compression tests. The third term has undergone considerable research and the indication is that this factor is not as important as one might at first suppose.

Special end plates or platens can be fabricated to reduce the friction effects if more refined test results are desired.

The test has been found to be somewhat sensitive to the rate of strain, but a strain rate between ½ and 2 percent/min appears to yield satisfactory results. Since the unconfined compression test specimens are exposed to the usually dry laboratory air (low humidity), specimen should reach failure within about min; otherwise, the change in water content may affect the unconfined compressive strength (increase it, usually).

The length to diameter ratio of the test specimens should be large enough to avoid interference of potential 45 failure planes and short enough that we do not obtain a “Column” failure. The length/diameter ratio to satisfy this criterion is 2 < L/d < 3.

It is conventional practice in soil mechanics to correct the area on which the load ‘P’ is acting. The original area is corrected by considering that the total volume of the soil is unchanged. The initial total soil sample volume is

Vt = A0L0 …………………………………………………………… Eq-1

But after some change in specimen length of ΔL

Vt = Af (L0- ΔL) …………………………………………………… Eq-2

Equating Eq-1 and Eq-2 for corrected area A we obtain,

Af = A0/1-є

APPARATUS:

· Unconfined Compression Device (Electrically driven strain controlled)

· Re-molding Device

· Deformation Dial Gage

· Balance (L.C. = 0.01 gms)

· Spatula

· Moisture tins

PROCEDURE:

· If density and moisture content of the soil is known, calculate the weight of the dry soil needed for preparation of three soil samples of 1.5” diameter and 3” height.

· Add specified moisture to the dry soil and mix thoroughly. Put some of the soil for moisture content determination.

· Prepare three soil samples of required density by packing the soil in the specimen mold.

· If the sample specimen crumbles easily or a good bearing surface for the plate cannot be obtained. It is permissible to cap the end using Plaster of Paris.

· If evaporation from the soil is expected, the samples should be sealed by encapsulating the specimens in a thin latex membrane immediately following specimen’s preparation.

· Carefully align the specimen in the compression machine.

· Set the load dial gage to zero and set the deformation dial to zero. At this time a very small load should be on the sample (order of ideal 1 unit of a loading gage).

· Turn on machine and take load and deformation dial readings as follows 10, 25, 50, 75, 100 and 50 to 100 dial divisions thereafter, until of the following:

· Load decreases on sample significantly.

· Load holds constant for 4 readings.

· Deformation is significantly past 15% strain.

· Remove the specimen from compression machine and sketch the failed specimen. If an obvious failure plane is observed, measure the angle of the failure plane with respect to the horizontal and record this angle as ф.

· Determine the water content of the sample.

· Test at least two more samples by repeating steps 6 to 10.

· Compute the unit strain, corrected area, and the unit stress, for all readings to define the stress-strain curve adequately. Plot the results on the graph paper from the test results, show qu as the peak stress of each test and calculate the average value of qu for three tests. Be sure to plot strain as the abscissa.

· Draw a Mohr’s Circle using average qu and draw three circles for three specimens and measure cohesion factor.


Height of specimen=cm

Diameter of specimen=cm

Area of specimen==cm2

Volume of Specimen=AreaHeight=cm3

Proving Ring Constant=lbs/div

Deformation dial gage constant=mm/div

Weight of soil sample=gm

Initial Moisture Content=%

Deformation Dial Gauge Reading


Sample Deformation

Strain

% Strain

Area Correction Factor

Corrected Area

Axial Load

Axial Stress

Col-1

Col-2

Col3=Col1*L.C

Col-3

Col-4 = Col-3 *100

Col-5 = 1-col3

Col-6

Col-7 = Col-2 * PRC

Col-8 = Col-7 / Col 6

lb

Mm

mm/mm

%

-

mm2

lb

kN

kPa

Graphs:

1. Graph between Strain and shear stress

2. Graph between normal stress and shear stress

Results:

=kPa (From graph)

su = Cu = kPa

Plot the Mohr’s circle between normal stress Ϭ and shear stress Ʈ and obtain corresponding undrained shear strength su of cohesive soil.

REFERENCE

ASTM D2166

Standard Test Method forUnconfined Compressive Strength of Cohesive Soil

COMMENTS:

Experiment # 5

Determination of Unconfined Compressive Strength of Cohesive Soils Stabilized with Cement

OBJECTIVE:

To perform unconfined compression test on cement stabilized cohesive soils to determine their unconfinedcompressive strength (qu) and undrained shear strength (su).

THEORY:

The geotechnical process of improving characteristics of soil is known as ground improvement. It has two types

1- Surface Stabilization

2- Deep ground improvement

Surface Stabilization

This method for stabilization can be grouped into:

· Mechanical Stabilization

· Physical Stabilization

· Chemical stabilization

· Physio-Chemical Stabilization

Mechanical Stabilization:

In this method mechanical energy is used to improve the soil mass and the method is known as compaction. For the embankmentof roads, railways, dams, levees, etc. generally rollers, vibratory plates, and tampers are used for compaction. Choice of roller or tamper usually depends on the degree of improvement required and the type of soil being compacted.

Physical Stabilization:

In this method the physical properties of the material (soil) are improved by blending two or three soils, together so as to improve the grading of mixture to well graded material. This technique is mostly used in road construction when more than one type of soils readily available at or near the site. In physical method some additiveslike cement, lime and bitumen are added in the soil.

Chemical stabilization

Chemical stabilizer also known as soil binders provides temporary soil stabilization. Materials made of vinyl, asphalt or rubbers are sprayed onto the surface of exposed soils to hold the soil in place and protect against erosion from runoff and wind. Chemical used for stabilization are easily applied to the surface of the soil, can be effective in stabilizing area where vegetative practice cannot be established, and provide immediate protection.

Physio-Chemical Stabilization

In this method of soil stabilization a combination of both physical and chemical methods such as lime stabilization are used.

APPARATUS:

· Unconfined Compression Device (Electrically driven strain controlled)

· Re-molding Device

· Deformation Dial Gage

· Balance (L.C. = 0.01 gm)

· Spatula

· Moisture tins

PROCEDURE

· Take some soil sample and do Modified Compaction Test.

· Calculate dry density and optimum moisture content.

· If density and moisture content of the soil is known, calculate the weight of the dry soil needed for preparation of 6 soil samples of 1.5” diameter and 3” height.

· Add specified amount of water and specified amount of cement to prepare six samples at varying percentages of cement (0%, 3%, 6%, 9%, 12% and15%) and mix them thoroughly.

· Put entire soil samples one by one in mold and prepare six samples to perform unconfined compression test.

· Carefully align the specimen in the compression machine.

· Set the load dial gage to zero and set the deformation dial to zero. At this time a very small load should be on the sample (order of ideal 1 unit of a loading gage).

· Turn on machine and take load and deformation dial readings as follows 10, 25, 50, 75, 100 and 50 to 100 dial divisions thereafter, until of the following:




· Remove the specimen from compression machine and sketch the failed specimen. If an obvious failure plane is observed, measure the angle of the failure plane with respect to the horizontal and record this angle as Ø.

· Determine the water content of the each sample.

· Compute the unit strain, corrected area, and the unit stress, for enough of the reading to define the stress-strain curve adequately. Plot the results on the graph paper from the test results, show qu as the peak stress of each test. Be sure to plot strain as the abscissa.

The test is performed on cohesive soil samples stabilized with different percentages of cement of the dry weight of specimen and optimum moisture content determined form modified Proctor’s compaction test.

OBSERVATIONS AND CALCULATIONS

Height of specimen=cm

Diameter of specimen=cm

Area of specimen==cm2

Volume of Specimen=AreaHeight=cm3

Proving Ring Constant=lbs/div

Deformation dial gage constant=mm/div

Weight of soil sample=gm

Initial Moisture Content=%

Percentage of cement added = %



Sample Deformation

Strain

% Strain


Corrected Area

Axial Load

Axial Stress

Col-1

Col-2

Col3=Col1*L.C

Col-3

Col-4 = Col-3 *100

Col-5 = 1-col3

Col-6

Col-7 = Col-2 * PRC

Col-8 = Col-7 / Col 6

Lb

mm

mm/mm

%

-

mm2

lb

KN

KPa

Graphs:

1. Graph between Strain and shear stress

2. Graph between normal stress and shear stress

Results:

=KPa (From graph)

su = Cu = KPa

Plot the Mohr’s circle between normal stress Ϭ and shear stress Ʈ and obtain corresponding undrained shear strength su of cement stabilized cohesive soils.

REFERENCE

ASTM DD5102

COMMENTS:

Experiment # 6

Determination of California Bearing Ratio of Laboratory Compacted Soils

OBJECTIVE

To determine the California bearing ratio on laboratory compacted soils by conducting a load penetration test in the laboratory.

NEED AND SCOPE

The California bearing ratio test is penetration test meant for the evaluation of sub-grade strength of roads and pavements. The results obtained by these tests are used with the empirical curves to determine the thickness of pavement and its component layers. This is the most widely used method for the design of flexible pavement.

THEORY

The design of flexible pavement is divided into three parts:

1. Determination the compaction characteristics of soil( AASHTO T-180 and ASTM D1557)

2. Determination of the CBR of the soil (AASHTO T193-93 and ASTM D1883)

3. Determination of the thickness of pavement on the bases of CBR

There are two methods to design the flexible pavement:

1. On the bases of GI (Group Index)

2. On the bases of CBR value

Group Index

Group index is used in the AASHTO soil classification system. Group index of the soil is calculated as

GI=0.01(F-15)(P-10)

Where:

GI= Group Index F=Percentage passing #200 Sieve PI=Plasticity Index

Greater will be the group index lower will be the quality of sub grade material.

C.B.R

CBR is the ratio of Load (Corrected) required to cause the specific penetration of the plunger to the standard load of the same penetration of the plunger. It is expressed as Percentage (%).

California Bearing Ratio (CBR) test was developed by the California Division of Highway as a method of classifying and evaluating soil-sub grade and base course materials for flexible pavements. CBR test, an empirical test, has been used to determine the material properties for pavement design. Empirical tests measure the strength of the material and are not a true representation of the resilient modulus. It is a penetration test wherein a standard piston, is used to penetrate the soil at a standard rate.

This test method is used to evaluate the potential strength of subgrade,sub base and base course material including recycled material for use in road and air field pavement. The CBR value obtains in this test in an integral part of several flexible pavement design method.

The following table gives the standard loads adopted for different penetrations for the standard material with a C.B.R. value of 100%

Penetration of plunger (mm)

Standard load (kg)

2.5

5.0

7.5

10.0

12.5

1370

2055

2630

3180

3600

CBR = × 100

Standred load for 0.1in penitration =3000 lb

Standard load for 0.2in penitrarion =4500 lb

Method of CBR test:

There are two method of CBR test

1- Point CBR (1 sample, 56 blows & compacted in 5 layers)

3-Point CBR (3 sample @ 10,30,65 blows in 5 layers)

PROCEDURE:

· Take soil sample and add specified amount of water and thoroughly mix it

· For 3-point un soaked CBR test put the soil sample in the mold and compact the soil in 5 layers by applying 10 no of blows in each layer

· Prepare two more sample and compact in 5 layers by applying 30 and 65 blows respectively.

· Put the sample in the CBR machine and set the dial gauge and load gauge zero.

· Turn on machine and take load at penetration as follows 60,120,180,240 and so on until of the following:




· Remove the specimen from compression machine.

· Take at least 3 samples

· Draw the graph b/w penetration and load and apply correction if needed.

· Calculate the penetration at 0.1 inch and 0.2 inch penetration and calculate the corresponding CBR values respectively.


O.M.C (form Modified Proctor’s compaction test) =%

Dry density (form Modified Proctor’s compaction test) =lbs/ft3Proving Ring Constant =lbs/Div

L.C of deformation dial gauge =inch/Div

Diameter of mould=inch

Height of mould=inch

Penetration dial gauge Reading

Load dial gauge Reading

Penetration mm

Penetration (in)

Load (lb)

Graph:

Graph between load vs penetration

Results:

Load at 0.1inch penetration=lb

CBR at 0.1inch penetration =%

Load at 0.2 inch penetration=lb

CBR at 0.2 inch penetration =%

REFERENCE

ASTM D1883

Standard Test Method for CBR (California Bearing Ratio) of Laboratory-Compact Soils

COMMENTS:

Experiment # 7

Performance of Consolidation Test on Cohesive Soils using Oedometer

OBJECTIVE

The objective of this experiment is to determine the compression index Cc and Cv.

NEED AND SCOPE OF THE EXPERIMENT

This test is performed to determine the magnitude and rate of volume decrease that a laterally confined soil specimen undergoes when subjected to different vertical pressures. From the measured data, the consolidation curve (pressure-void ratio relationship) can be plotted. This data is useful in determining the compression index, the recompression index and the pre-consolidation pressure (or maximum past pressure) of the soil. In addition, the data obtained can also be used to determine the coefficient of consolidation and the coefficient of secondary compression of the soil.

SIGNIFICANCE:

The consolidation properties determined from the consolidation test are used to estimate the magnitude and the rate of both primary and secondary consolidation settlement of a structure or an earth fill. Estimates of this type are of key importance in the design of engineered structures and the evaluation of their performance.

THEORY:

Introduction

All soils are compressible so deformation will occur whenever stress is applied to soils. Soil minerals and water are both incompressible. Therefore, when saturated soils are loaded, the load first acts on the pore water causing pore water pressures that are in excess of the hydrostatic pressures. The excess pore water pressures are largest near the application of load and decrease with distance from the loading. The variations in excess pore water pressure cause total head gradients in the soil which, according to Darcy’s Law, will induce water to flow from locations of high total head to low total head. The excess pore water pressures dissipate as water flows from the soil and, to compensate for the applied stress, the stress is transferred to the soil minerals resulting in higher effective soil stress. The flow of water from the soil also causes reductions in the soil volume and settlements at the ground surface. Fine-grained soils have very low permeability so they can require substantial periods of time before the excess pore water pressures fully dissipate. This process of time-dependent settlement is referred to as consolidation. Terzaghi’s theory for one-dimensional consolidation provided the means to calculate the total amount of consolidation settlement and the consolidation settlement rate. In practice, engineers obtain representative soil samples, conduct consolidation tests and use Terzaghi’s consolidation theory to predict the total settlement and time rate of settlement for embankments and foundations.

When a compressive load is applied to soil mass, a decrease in its volume takes place, the decrease in volume of soil mass under stress is known as compression and the property of soil mass pertaining to its tendency to decrease in volume under pressure is known as compressibility. In a saturated soil mass having its void filled with incompressible water, decrease in volume or compression can take place when water is expelled out of the voids. Such a compression resulting from a long time static load and the consequent escape of pore water is termed as consolidation. Then the load is applied on the saturated soil mass, the entire load is carried by pore water in the beginning. As the water starts escaping from the voids, the hydrostatic pressure in water gets gradually dissipated and the load is shifted to the soil solids which increases effective on them, as a result the soil mass decrease in volume. The rate of escape of water depends on the permeability of the soil. Major problem in the soil is the soil subsidence caused by pressure or weight of construction trucks on the surface, which may be divided into three categories.

· Elastic Deformation

· Primary Consolidation

· Secondary Consolidation

APPARATUS

1. Consolidation device (including ring, porous stones, water reservoir, and load plate)

2. Dial gauge (0.0001 inch = 1.0 on dial)

3. Sample trimming device

4. Glass plate

5. Metal straight edge

6. Clock

7. Moisture can

8. Filter paper

PROCEDURE

1. Weigh the empty consolidation ring together with glass plate

2. Measure the height (h) of the ring and its inside diameter (d).

3. Extrude the soil sample from the sampler, generally thin-walled Shelby tube. Determine the initial moisture content and the specific gravity of the soil as per Experiments 1 and 4, respectively (Use the data sheets from these experiments to record all of the data).

4. Cut approximately a three-inch long sample. Place the sample on the consolidation ring and cut the sides of the sample to be approximately the same as the outside diameter of the ring. Rotate the ring and pare off the excess soil by means of the cutting tool so that the sample is reduced to the same inside diameter of the ring. It is important to keep the cutting tool in the correct horizontal position during this process.

5. As the trimming progresses, press the sample gently into the ring and continue until the sample protrudes a short distance through the bottom of the ring. Be careful throughout the trimming process to insure that there is no void space between the sample and the ring.

6. Turn the ring over carefully and remove the portion of the soil protruding above the ring. Using the metal straight edge, cut the soil surface flush with the surface of the ring. Remove the final portion with extreme care.

7. Place the previously weighed Saran-covered glass plate on the freshly cut surface, turn the ring over again, and carefully cut the other end in a similar manner.

8. Weigh the specimen plus ring plus glass plate

9. Carefully remove the ring with specimen from the Saran-covered glass plate and peel the Saran from the specimen surface. Center the porous stones that have been soaking, on the top and bottom surfaces of the test specimen. Place the filter papers between porous stones and soil specimen. Press very lightly to make sure that the stones adhere to the sample. Lower the assembly carefully into the base of the water reservoir. Fill the water reservoir with water until the specimen is completely covered and saturated.

10. Being careful to prevent movement of the ring and porous stones, place the load plate centrally on the upper porous stone and adjust the loading device.

11. Adjust the dial gauge to a zero reading.

12. With the toggle switch in the down (closed) position, set the pressure gauge dial (based on calibration curve) to result in an applied pressure of 0.5 tsf (tons per square foot).

13. Simultaneously, open the valve (by quickly lifting the toggle switch to the up (open) position) and start the timing clock.

14. Record the consolidation dial readings at the elapsed times given on the data sheet.

15. Repeat Steps 11 to 13 for different preselected pressures (generally includes loading pressures of 1.0, 2.0, 4.0, 8.0, and 16.0 tsf and unloading pressures of 8.0, 4.0, 2.0, 1.0 and 0.5 tsf)

16. At the last elapsed time reading, record the final consolidation dial reading and time, release the load, and quickly disassemble the consolidation device and remove the specimen. Quickly but carefully blot the surfaces dry with paper toweling. (The specimen will tend to absorb water after the load is released.)

17. Place the specimen and ring on the Saran-covered glass plate and, once again, weigh them together.

18. Weigh an empty large moisture can and lid

19. Carefully remove the specimen from the consolidation ring, being sure not to lose too much soil, and place the specimen in the previously weighed moisture can. Place the moisture can containing the specimen in the oven and let it dry for 12 to 18 hours.

20. Weigh the dry specimen in the moisture can

OBSERVATIONS & CALCULATIONS:

Diameter of ring=mm

Height of Ring=mm

L.C of dial gauge=mm/Div

Area=cm2

Volume=cm3

Before test:

Weight of empty ring=gm

Weight of ring+ wet soil=gm

After test:

Weight of ring+ wet soil=gm

Weight of ring+ dry soil=gm

For moisture content

Weight of empty container=gm

Weight of container+ wet soil=gm

Weight of container+ dry soil=gm

=cm

where

= Specific gravity of soil

= Weight of dry soil after test=gm

=1gm/cm3

=cm2

= H - Hs=cm

=Initial void ratio=

Initial dial gauge reading(first day) =

Final dial gauge reading (At end of loading) =

Change in sample height== (Initial D.G Reading - Final D.G Reading) * L.C =mm

Final height of sample= = H - =cm

Final volume==cm3

Final void ratio= =

Bulk density of soil=gm/cm3

Moisture Content==%

Dry density of the soil=gm/cm3

Experiment# 8

Performance of Standard Penetration Test (SPT)

OBJECTIVE:

The purpose of this experiment is to collect the soil sample and to determine the penetration resistant (N value) of a soil which can be related to unconfined compression strength.

THEORY:

SPT N value is No. of blows count per ft of penetration of an 18” deep sampler using a 140lb hammer dropping 30” (2.5’) freely pushing a 2” outer diameter sampler and receiving one hole of soil sample. SPT test give disturbed sample.

The Standard Penetration test (SPT) is a common in situ testing method used to determine the geotechnical engineering properties of subsurface soils. It is a simple and inexpensive test to estimate the relative density of soils and approximate shear strength parameters.

SPT (Standard Penetration Test) is a dynamic, in situ penetration test used for providing information on geotechnical engineering properties of soil. The test takes place inside a borehole, using a thick-walled sample tube. This tube has an outside diameter of 50mm with an inside diameter of 35mm. The sample tube is driven from the bottom of the borehole into the ground using a 63.5kg hammer, which is dropped freely through a distance of 760mm. The test results are deduced through the number of blows needed to drive the tube each 75mm into the ground, to a maximum depth of 450mm. The “standard penetration resistance” or “N-value” is calculated by the sum of the number of blows required for the last four 75mm increments of penetration, to a maximum of 50 blows.

Should the total number of blows for the last four increments total 50 or more, the test is stopped and the penetration measured in millimeters. In these cases the blow count provides an indication of ground density, useful in many empirical geotechnical engineering formulae.

An SPT is particularly used to indicate relative density of granular deposits which make obtaining undisturbed samples virtually impossible to recover, such as gravels and sands. It is a widespread test as it provides the date through a simple and inexpensive means. Although approximate results within soil parameters are recovered, the data gives a useful guide where borehole samples are not practical or possible. It can also be used in conjunction with samples, alternating sampling with SPTs to check the strength of the ground between removing samples.

SPT equipment can also be used to push beyond standard test parameters, to assess deposit stability in granular soils below groundwater level. Although this is not strictly an Standard Penetration Test, it is useful to indicate whether the deposit is as loose as the standard test results indicate.

The SPT results vary in usefulness according to the soil type, with the fine and more granular soil types such as fine sand yielding results at the higher end of the accuracy spectrum, and more dense soil types such as clay giving data that may not truly represent the soil conditions being tested. Location and environment can play a part in this, for example more arid areas have been noticed to display natural cementation, which increases the Standard Penetration Value.

Correlation between SPT-N value, friction angle, and relative density

Correlation between SPT-N value and friction angle and Relative density (Meyerhoff 1956)

SPT N3 [Blows/0.3 m - 1 ft]

Soi packing

Relative Density [%]

Friction angle[°]

< 4

Very loose

< 20

< 30

4 -10

Loose

20 - 40

30 - 35

10 - 30

Compact

40 - 60

35 - 40

30 - 50

Dense

60 - 80

40 - 45

> 50

Very Dense

> 80

> 45

APPARATUS:

· SPT sampler with extension rods

· Tripod stand

· Rope with hammer

· Miscellaneous

PROCEDURE

· The bore hole is advanced to desired depth and bottom is cleaned.

· Split spoon sampler is attached to a drill rod and rested on bore hole bottom.

· Driving mass is dropped onto the drill rod repeatedly and the sampler is driven into soil for a distance of 450 mm. The number of blow for each 150 mm penetration are recorded.

· N-value

1. First 150 mm penetration is considered as seating penetration

2. The number of blows for the last two 150 mm penetration are added together and reported as N-value for the depth of bore hole.

· The split spoon sampler is recovered, and sample is collected from split barrel so as to preserve moisture content and sent to the laboratory for further analysis.

· SPT is repeated at every 750 mm or 1500 mm interval for larger depths.

· Under the following conditions the penetration is referred to as refusal and test is halted

a) 50 blows are required for any 150 mm penetration

b) 100 blows are required for last 300 mm penetration

c) 10 successive blows produce no advancement

PRECAUTIONS:

· The height of free fall Must be 750 mm

· The fall of hammer must be free, frictionless and vertical

· Cutting shoe of the sampler must be free from wear & tear

· The bottom of the bore hole must be cleaned to collect undisturbed sample

· When SPT is done in a sandy soil below water table, the water level in the bore hole MUST be maintained higher than the ground water level.

THE UNIVERSITY OF LAHORE Hole No:________

SOIL LOG SUBSURFACE EXPLORATION Sheet_____of_____

Job No _______________ Project Location: __

Type of Boring: Auger Boring_____ Co-Ordinates:______________ Elevation:______________

Sampler Hammer Wt:____________ Contractor:________________ Date________to_________

Drop:__30 inch_____ Ground Water Level:________ Inspector:______________

Depth (ft)

Elevation ft/M

Color

DESCRIPTION OF MATERIAL

SPT

Blows/ft

REMARKS

REFERENCE

ASTM D1586

Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils

COMMENTS:

Experiment # 9

Performance of Tri-Axial Compression Test on Cohesive Soils under Un-Consolidated Un-Drained Condition

OBJECTIVE

1. This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of either undisturbed or remolded cohesive soil.

2. This test method provides data for determining undrained strength properties (Cuu&φuu) and stress-strain relations for soils.

SIGNIFICANCE AND USE

· In this test method, the compressive strength of a soil is determined in terms of the total stress, therefore, the resulting strength depends on the pressure developed in the pore fluid during loading. In this test method, fluid flow is not permitted from or into the soil specimen as the load is applied, therefore the resulting pore pressure, and hence strength, differs from that developed in the case where drainage can occur.

· If the test specimens are 100 % saturated, consolidation cannot occur when the confining pressure is applied nor during the shear portion of the test since drainage is not permitted. Therefore, if several specimens of the same material are tested, and if they are all at approximately the same water content and void ratio when they are tested, they will have approximately the same undrained shear strength. The Mohr failure envelope will usually be a horizontal straight line over the entire range of confining stresses applied to the specimens if the specimens are fully saturated.

· If the test specimens are partially saturated or compacted specimens, where the degree of saturation is less than 100 %, consolidation may occur when the confining pressure is applied and during shear, even though drainage is not permitted. Therefore, if several partially saturated specimens of the same material are tested at different confining stresses, they will not have the same undrained shear strength. Thus, the Mohr failure envelope for unconsolidated undrainedtriaxial tests on partially saturated soils is usually curved.

· The unconsolidated undrainedtriaxial strength is applicable to situations where the loads are assumed to take place so rapidly that there is insufficient time for the induced pore-water pressure to dissipate and for consolidation to occur during the loading period (that is, drainage does not occur).

· Compressive strengths determined using this procedure may not apply in cases where the loading conditions in the field differ significantly from those used in this test method.

THEORY

Back pressure

A pressure applied to the specimen pore-water to cause air in the pore space to compress and to pass into solution in the pore-water thereby increasing the percent saturation of the specimen.

Effective consolidation stress

The difference between the cell pressure and the pore-water pressure prior to shearing the specimen

Failure

The stress condition at failure for a test specimen. Failure is often taken to correspond to the maximum principal stress difference (maximum deviator stress) attained or the principal stress difference (deviator stress) at 15 % axial strain, whichever is obtained first during the performance of a test. Depending on soil behavior and field application, other suitable failure criteria may be defined, such as maximum effective stress obliquity, s81/s83, or the principal stress difference (deviator stress) at a selected axial strain other than 15 %.

APPARATUS

· Axial Loading Device

· Axial Load-Measuring Device

· Triaxial Compression Chamber

· Axial Load Piston

· Pressure Control Device

· Specimen Cap and Base

· Deformation Indicator

· Rubber Membrane

· Sample Extruder

· Specimen Size Measurement Devices

· Timer

· Balances

· Miscellaneous Apparatus

PROCEDURE

1. Place the membrane on the membrane expander or, if it is to be rolled onto the specimen, place the membrane onto the cap or base. Place the specimen on the base.

2. Place the rubber membrane around the specimen and seal it at the cap and base with O-rings or other positive seals at each end. A thin coating of silicon grease on the vertical surfaces of the cap or base will aid in sealing the membrane.

3. With the specimen encased in the rubber membrane, which is sealed to the specimen cap and base and positioned in the chamber, assemble the triaxial chamber.

4. Bring the axial load piston into contact with the specimen cap several times to permit proper seating and alignment of the piston with the cap.

5. When the piston is brought into contact the final time, record the reading on the deformation indicator to three significant digits.

6. During this procedure, take care not to apply an axial stress to the specimen exceeding approximately 0.5 % of the estimated compressive strength. If the weight of the piston is sufficient to apply an axial stress exceeding approximately 0.5 % of the estimated compressive strength, lock the piston in place above the specimen cap after checking the seating and alignment and keep locked until application of the chamber pressure.

7. Place the chamber in position in the axial loading device. Be careful to align the axial loading device, the axial load-measuring device, and the triaxial chamber to prevent the application of a lateral force to the piston during testing.

8. Attach the pressure-maintaining and measurement device and fill the chamber with the confining liquid. Adjust the pressure maintaining and measurement device to the desired chamber pressure and apply the pressure to the chamber fluid.

9. Wait approximately 10 min after the application of chamber pressure to allow the specimen to stabilize under the chamber pressure prior to application of the axial load.

10. Slightlyabove the specimen cap, and before the piston comes in contact with the specimen cap, either: (1) measure and record the initial piston friction to three significant digits and upward thrust of the piston produced by the chamber pressure and later correct the measured axial load, or (2) adjust the axial load-measuring device to compensate for the friction and thrust. If the axial load-measuring device is located inside the chamber, it will not be necessary to correct or compensate for the uplift force acting on the axial loading device or for piston friction. In both cases record the initial reading on the deformation indicator when the piston contacts the specimen cap.

11. Apply the axial load to produce axial strain at a rate of approximately 1 %/ min for plastic materials and 0.3 % / min for brittle materials that achieve maximum deviator stress at approximately 3 to 6 % strain. At these rates, the elapsed time to reach maximum deviator stress will be approximately 15 to 20 min. Continue the loading to 15 % axial strain, except loading may be stopped when the deviator stress has peaked then dropped 20 % or the axial strain has reached 5 % beyond the strain at which the peak in deviator stress occurred.

12. Record load and deformation values to three significant digits at about 0.1, 0.2, 0.3, 0.4, and 0.5 % strain; then at increments of about 0.5 % strain to 3 %; and, thereafter at every 1 %.

13. Take sufficient readings to define the stress-strain curve; hence, more frequent readings may be required in the early stages of the test and as failure is approached.



Height=inch

Area=in2

Volume=in3

Moisture Content=%

Bulk Density=lb/ft3

Wet weight for one sample=gm

Proving ring constant=lb/Div

Least count of deformation dial gauges = mm/Div

Applied lateral stress Ϭ3 =kPa



Sample Deformation

Strain

% Strain


Corrected Area

Axial Load

Axial Stress

Col-1

Col-2

Col-3=Col1*L.C

Col-3

Col-4

Col-5

Col-6

Col-7

Col-8

lb

Mm

mm/mm

Col3*100

1-col3

mm2

lb

KN

kPa

Results:

Plot the Mohr’s circle between normal stress Ϭ and shear stress Ʈ and obtain corresponding unconsolidated un-drained shear strength parameters (cuu and φuu) of given soil specimen.

REFERENCE

ASTM D2850

Standard Test Method for Unconsolidated-UndrainedTriaxial Compression Test on Cohesive Soils

COMMENTS:

Experiment#10

Performance of Tri-Axial Compression Test on Cohesive Soils under Consolidated Un-Drained Condition

OBJECTIVE

1. This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of either undisturbed or remolded cohesive soil.

2. This test method provides data for determining consolidated undrained shear strength properties (Ccu&φcu) and stress-strain relations for soils.

THEORY

The triaxial compression test is a procedure that permits different horizontal and vertical stresses to be applied to the soil specimen simultaneously and thus closely duplicate the expected field conditions.

Usually the principle change in stress experienced by soil is a change in vertical stress due to the construction of a building, highway, airport, bridge, dam or other structure on the surface above the supporting soil. Consequently, it would be logical to test the soil specimen in a configuration that permits the specimen to be placed in the testing device and loaded in a manner that duplicates what will happen in the fluid. The vertical load being applied to the soil specimen causes it to feel a vertical stress that is increasingly larger than the confining pressure. This increase in vertical pressure is called the deviator stress (σ).when the deviator stress is being applied, (ϕ1), the major principle stress is no longer equal to (ϕ3) thus (ϕ1) now becomes ϕ1 = ϕ3+ σ

The length diameter ratio of the test specimen should be large enough to avoid interference of potential 45 degree failure planes and short enough that we do not obtain a column failure. The length diameter ratio to satisfy this criterion is 2< L/d<3

It is conventional practice in soil mechanics to correct the area on which the load “P” is acting. The original area Aₒ

Is corrected by considering that the total volume of the soil is unchanged. The initial total soil sample volume is (Vt = Aₒ Lₒ) Eq.a, but for some change in specimen length of ΔLVt = A (Lₒ- ΔL) Eq.2

Equating Eqs. (a) And (b), cancelling terms and solving for the corrected area A, we obtain. A’ = (Aₒ/1-є)

There are three basic types of triaxial compression test procedures as determined by the sample condition: the un-consolidated UN drained (UU) test, the consolidated UN drained (CU), and the consolidated drained (CD) test.

The consolidated un-drained (CU) test is performed by placing the sample in the chamber and introducing the confined pressure. The sample is then allowed to consolidate under the all-around containing pressure by leaving the drain lines open. The drain lines are then closed and the axial stress increased without allowing further drainage.

The consolidated drained (CD) test is similar to the CU test expect that the sample is allowed to drain as the axial load is applied so that high excess pore pressures not to be developed. The consolidated drained test is often referred to as the slow or S test.

APPARATUS:

1. Triaxial compression device (electrically driven controlled device)

2. Triaxial cell

3. Specimen mould

4. Rubber membrane (typically 1.4” or 2.8” diameter)

5. Membrane stretcher and ruler binding strips.

Required parameters:

1. Diameter of soil specimen

2. Height of soil specimen

3. Proving ring constant

PROCEDURE:

· If density and moisture content of the soil is known, calculate the weight of the dry soil needed for proportion of three soil samples of 1.5” diameter and 3” height.

· Add specified moisture to the dry soil and mix thoroughly put some of the soil for moisture content determination.

· Prepare three soil samples of required density by packing the soil in the specimen mould.

· Take the correct size membrane stretcher and membrane and fit the membrane smoothly into the stretcher, folding the ends of the membrane over the ends of the stretcher.

· Insert the sample into the membrane and attach the lower platen using rubber bands or strips to seal the membrane.

· Remove the sample from the membrane stretcher and attach the lower platen to the base of the triaxial cell. Also attach the upper platen if this has not already been done. Use extreme case not to damage the soil specimen.

· Place and Lucite cover on the cell and place the cell in the compression machine. Bring the load bar in contact with the load piston until a load just flickers on the load dial.

· Apply a pre-determined chamber pressure for the lateral pressure σ3.

· Attach a deformation dial to the machine so that the sample deformation can be obtained. Set the dial gauge to zero, then manually compress and release the dial plunger several times and observe the zero reading.re adjust the gauge to zero if necessary.

· Check deformation dial gauge and cell pressure gauge for final correct settings.

· Set the compression machine to the desired rate (generally between 0.5 to 1.25 mm/min).

· Turn on the compression machine and take simultaneous load and deformation readings. Readings may be taken at 5,15,25,50 and every 50 to 100 divisions or as specified until.

a) Load peaks and then falls off.

b) Somewhat past 20% strain.

c) Load holds constant for 3 or 4 successive readings.



Height=inch

Area=inch2

Volume=inch3

Proving ring constant=lbs/Div

Least count of deformation dial gauges=mm/Div

Applied lateral stress Ϭ3 =kPa



Sample Deformation

Strain

% Strain


Corrected Area

Axial Load

Axial Stress

Col-1

Col-2

Col-3=Col1*L.C

Col-3

Col-4

Col-5

Col-6

Col-7

Col-8

lb

mm

mm/mm

Col3*100

1-col3

mm2

lb

kN

kPa

Graphs:

1. Graph between axial stress and deviated stress

2. Mohr’s circle

Results:

Plot the Mohr’s circle between normal stress Ϭ and shear stress Ʈ and obtain corresponding consolidated un-drained shear strength parameters (ccu and φcu) of given soil specimen.

REFERENCE

ASTM D4767

Standard Test Method for Consolidated UndrainedTriaxial Compression Test for Cohesive Soils

COMMENTS:

Experiment# 11

Determination of Coefficient of Permeability by Constant Head Apparatus

OBJECTIVE:

This test method measures hydraulic conductivity also known as coefficientofpermeability) of materials with a rigid-wall mold permeameter.Such materials can be tested whose hydraulic conductivity is less than or equal to 1 x 10−5 cm/sec.

SIGNIFICANCE AND USE:

1. This test method applies to one-dimensional, laminar flow of water within laboratory-compacted, porous materials

2. The hydraulic conductivity of porous materials generally decreases with an increasing amount of air in the pores of the material. This test method applies to porous materials containing little or no air.

3. The test method is designed to minimize the amount of air in the test specimen.

THEORY:

1. Hydraulicconductivity(k):

The rate of discharge of water under laminar flow conditions through a unit cross-sectional area of a porous medium under a unit hydraulic gradient and standard temperature conditions (20°C).

2. Hydraulic gradient:

The hydraulicgradient is a vector gradient between two or more hydraulic head measurements over the length of the flow path.

Where h2 and h1 are the piezometric heads and length is the length of flow between two

piezometers.

3. Darcy Law:

Darcy's law states that flow rate is directly proportional to the drop in vertical elevation between two places in the medium and inversely proportional to the distance between them.

Assumptions:

1. Test is valid only for permeamation of materials with water only.

2. Darcy law is valid.(validity of Darcy law can be tested by measuring hydraulic conductivity of specimen at three different gradients , if measured values are similar then Darcy law is valid)

3. Level of effective stress is controlled.

4. Result of laboratory test could not be applied to in-place materials directly, it may vary.

The test method is applicable to that material whose shrinkage is minimal when exposed to water.

APPARATUS:

1. Constant Head:

The system must be capable of maintaining a constant head to within -/+5 %. In addition, the head loss across the test specimen must be held constant to within -/+ 5 %. Pressures shall be measured by a pressure gage, electronic pressure transducer. Head of liquid in a standpipe may be measured with a graduated pipette, ruler, and scale.

2. Permeameter Cell:

The permeameter cell shall consist of a rigid-wall compaction mold into which the material to be tested is compacted and in which the compacted material is permeated; and two end plates to control flow into and out of the test specimen. The permeameter shall be designed and operated so that permeant water flows downward through the test specimen.

3. Beaker

4. Weighing Balance

5. Hammer

6. Can

PROCEDURE:

1. First of all connect the reservoir of constant head apparatus to three lines. One line is intake and is connected to a tap for the supply of water. One line is the overflow discharge line and is used to drain out the excess water to maintain a constant head. Another line is the test line, it is connected to the test cylinder and it contains valve.

2. Place porous plate at the bottom of the test cylinder to avoid the passing of soil particles. Take 1 kg of soil sample and fill the test cylinder into three layers by slightly compacting each layer. Use a small hammer for compaction.

3. Connect intake line to the head of test cylinder. Connect the tubes of two manometers to outlets present at the surface of test cylinders. Close the valve present at intake outlet before filling the reservoir.

4. When level of water is constant in the reservoir open the intake valve and let the water run through test cylinder that keeps it flowing for some time to completely saturate the sample and also to remove air voids present in cylinder.

5. Now collect the specific volume of water in a pre-weighed beaker and record time needed to collect the specific quantity of water.

6. Similarly collect two more samples of different volumes and record time of collection. Measure the heads at two manometers from the bottom of test cylinder.

7. Calculate co-efficient of permeability for all the three volumes collected and report the average of three as co-efficient of permeability.

OBSERVATIONS & CALCULATIONS:

Diameter of Premeameter = cm

Length =cm

Area =cm2

Volume =cm3

Dry density =g/cm3

Time =sec

Sr#

H1 (cm)

H2 (cm)

H=H1-H2 (cm)

Volume (cm3)

Q=V/t (cm3/sec)

Temp ⁰C

Kt=QL/AhT (cm/sec)

K20=ȵT/ȵ20*KT (cm/sec)

REFERENCE

ASTM D2434

Standard Test Method for Permeability of Granular Soils (Constant Head)

COMMENTS:

Experiment#12

Determination of Coefficient of Permeability by Falling Head Apparatus

OBJECTIVE

This test method measures hydraulic conductivity also known as co-efficient of permeability of fine grained materials (soils) with a rigid-wall mold permeameter. Such materials can be tested whose hydrullic conductivity is less than or equal to 10-3 to 10-6cm per sec.

NEED AND SCOPEOF THE EXPERIMENT:

1. This test method applies to one-dimensional, laminar flow of water within laboratory-compacted, porous materials

2. The hydraulic conductivity of porous materials generally decreases with an increasing amount of air in the pores of the material. This test method applies to porous materials containing little or no air.

3. The test method is designed to minimize the amount of air in the test specimen.

THEORY

Falling Head Permeability Test Apparatus

The general expression for k is

APPARATUS:

1. Falling Head:

The system shall allow for measurement of the applied head loss, thus hydraulic gradient, to within -/+5 % or better at any time. In addition, the ratio of initial head loss divided by final head loss over an interval of time shall be measured such that this computed ratio is accurate to within -/+ 5 %. The head loss shall be measured with a pressure gage, electronic pressure transducer, engineer’s scale, graduated pipette, or any other device of suitable accuracy. Falling head tests may be performed with either a constant tail-water elevation (Test Method B), rising tail-water elevation (Test Method C), or increasing tail-water elevation (Test Method D).

2. Premeameter Cell:

The Premeameter cell shall consist of a rigid-wall compaction mold into which the material to be tested is compacted and in which the compacted material is permeated. Unlike Constant head test the Premeameter cell in this case consist of porous stone at the top and bottom instead of porous disc. The Premeameter shall be designed and operated so that permeant water flows downward through the test specimen. Cell is made so as to perform test on clays and very very fine grained soils.

3. Beaker

4. Weighing Balance

5. Hammer

PROCEDURE:

1. Take the soil sample of 1 kg into a pre-weighed container. Now Place a porous stone at the bottom of test cylinder and pour the soil into the test cylinder in three layers.

2. Compact each layer by hammer to achieve a compacted mass. Level the soil at the top and place other porous stone and cap onto the surface and tight the three nuts/clamps.

3. The test cylinder is connected to a monomeric head which is connected directly to the reservoir. The whole assembly contains three valves, one at the bottom of the test cylinder,other at top of the test cylinder and the rest is attached at the bottom of monomeric column.

4. Open all the three valves and start pouring water into the manometric column.

5. Let the sample saturate completely and make sure that air bubbles are removed completely through bottom valve of test cylinder.

6. Close the valve and let the water rise into the manometric column to a specific height. Now open the valve and let the manometric column drop to a specific height.

7. Record the time accounting for the drop of water at the same time. Perform the same for two more readings.

8. Calculate the co-efficient of permeability for all three falling heads and report the average of the three as co-efficient of permeability of representative sample.


Mass of container at initial volume of soil =gm

Mass of container and remaining soil =gm

Mass of soil in cylinder =gm

Height of soil sample in the cylinder =cm

Diameter of Sand Pipe =cm

Internal Diameter of Test Cylinder =cm

Cross-sectional area of sand pipe = a = cm2

Cross-sectional area of the soil column = A =cm2

Trial number

h0

h1

Time

K

-

cm

cm

sec

cm/sec

Co-efficient of permeability:

Where

a=cross-sectional area of sand pipe

L=length of soil column

A=cross-sectional area of the soil column

t=time interval for head to drop

h0=total head before the test

h1=total head after the test

REFERENCE

ASTM D5084

Standard Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials using a Flexible Wall Permeameter

COMMENTS:

1

Graph b/w Axial Stress vs %strain

Group-100.328083989501314840.656167979002624580.984251968503936591.312335958005251.64041994750657061.96850393700787412.29658792650918642.62467191601049922.95275590551178223.28083989501312353.60892388451444023.93700787401574774.26509186351704454.59317585301836750168.07832573559878254.38992494359263355.58813372012423422.21006584703224469.95171985080663502.05884790716965524.78730948105181535.18846986231983548.53826495372289552.7245475894465556.86984850577846556.47437491366952556.06865589169786554.16300594004804

%Strain

Axial Stress (kpa)

23

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