SOIL CLASSIFICATION AND SOIL TESTING (Part - 2)

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SL NO	NAME OF TEST
6	CONSISTENCY LIMITS OF SOILS.
7	COMPACTION TEST.
8	FIELD DENSITY TEST BY SAND REPLACEMENT METHOD.
9	CALIFORNIA BEARING RATIO TEST.
10	SHEAR TEST BY TRIAXIAL METHOD.
11	SAND EQUIVALENT TEST
12	BEARING CAPACITY OF SOIL BY PLATE LOAD BEARING TEST.

 

6.CONSISTENCY LIMITS OF SOILS.

( IS : 2720 – PART – 5 )

 

INTRODUCTION:

The physical properties of fine-grained soils, especially of clay differ much at different water contents. Clay may be almost in liquid state, or it may show plastic behavior or may be very stiff depending on the moisture content. Plasticity is a property of outstanding importance for clayey soils, which may be explained as the ability to undergo changes in shape without rupture.

Atterberg in 1911 proposed a series of tests, mostly empirical, for the determination of the consistency and plastic properties of fine soils. These are known as Atterberg limits and indices.

Liquid limit: defined as the minimum water content at which the soil will flow under the application of a very small shearing force.

Plastic Limit: defined as the minimum moisture content at which the soil remains in a plastic state.

Plasticity Index (PI): is defined as the numerical difference between the liquid limit and plastic limits. PI thus indicates the range of moisture content over which the soil is in a plastic condition.

Shrinkage Limit: is the maximum moisture content at which further reduction in water content does not cause reduction in volume. It is the minimum water content that can occur in a clayey soil sample, which is completely saturated.

Consistency limits and the plasticity index vary for different soil types. Hence these properties are generally used in the identification and classification of soils.

Liquid limit test:(Mechanical liquid limit device)

Object:

Determination of the liquid limit of soil by mechanical liquid limit device.

Apparatus:

i) Mechanical liquid limit device consists of a cup and arrangement for raising and dropping through a specified height and standard grooving tools.

ii) Balance of 200 g capacity and sensitive to 0.01 g.

iii) Oven to maintain 105  to 110 deg. C

  

Procedure:

About 120 g of dry pulverized soil sample passing 425 micron IS sieve is weighed, and mixed thoroughly with distilled water in the evaporating dish to form a uniform thick paste. The liquid limit device is adjusted to have a free fall of cup through 10 mm. A portion of the paste is placed in the cup above the lowest spot, and squeezed down with the spatula to have a horizontal surface. The specimen is trimmed by firm strokes of spatula in such a way that the maximum depth of soil sample in the cup is 10 mm. The soil in the cup is divided along the diameter through the center line of the cam followed by firm strokes of the grooving tool so as to get a clean sharp groove. Grooving tool (b) may be used for all soils, where as grooving tool (a) may be used only in clayey soils free from sand particles or fibrous materials.

The crank is rotated at the rate of two revolutions per second (either by hand or electrically operation) so that the cup is lifted and dropped. This is continued till the two halves of the soil cake come into contact at the bottom of the groove along a distance of about 10 mm, and the number of blows given is recorded. A representative soil is taken, placed in the moisture container, lid placed over it and weighed. The container is dried in oven and the dry weight determined the next day for finding the moisture content of the soil. The operations are repeated for at least three more trials with slightly increased moisture contents each time, noting the number of blows so that there are at least four uniformly distributed readings of number of blows between 10 and 40 blows.

Calculations:

Taking the number of blows in the log scale on the X-axis, and the water content in arithmetic scale on the Y-axis plots the flow curve. The flow curve is straight line drawn on this semi-logarithmic plot, as nearly as possible through three or more plotted points.

The moisture content corresponding to 25 blows is read from this curve, rounding off to the nearest whole number and is reported as the liquid limit (LL or wl) of the soil.

The slope of the straight-line flow curve is the flow index. It may be calculated from the following formula:

Flow Index (If) =   { (w1 – w2 ) /  (log n2 – log n1) }    =   {(w10 – w100)  /  ( log 100 – log 10) } 

                            

 Where,         w10 = water content at 10 blows.

w100 = water content at 100 blows.

 

Liquid limit test: (Cone penetration)

Object:

To determine the liquid limit of the soil by cone penetration apparatus.

Apparatus:

i) Cone penetration apparatus confirming to IS: 11196-1985 (cone angle 300+/-0.50) and weight of assemble is 80 +/- 0.5 g including all).

ii) Balance of 200 g capacity and sensitive to 0.01 g.

iii) Oven to maintain 105 to 110 deg. C.

             

Procedure:

About 150 g of dry pulverized soil sample passing 425 micron IS sieve is weighed, and mixed thoroughly with distilled water in the evaporating dish to form a uniform thick paste. The soil paste shall then be transferred to the cylindrical mould of the cone penetrometer apparatus and leveled up to the top of the cup. The penetrometer shall be so adjusted that the cone point just touches the surface of the soil paste in the trough. The scale of the penetrometer shall then be adjusted to zero and the vertical rod released so that the cone is allowed to penetrate into the soil paste under its weight. The weight should be 80 +/- 0.5 g and the penetration shall be noted after 5 seconds from the release of the cone.

If the difference in penetration lies between 14 and 28 mm the test is repeated with suitable adjustments to moisture either by addition of more water or exposure of the spread paste on a glass plate for reduction in moisture content. The test shall be repeated at least to have four sets of values of penetration in the range 14 and 28 mm. The exact moisture content of each trial shall be determined.

Calculations:

A graph representing water content on the Y-axis and the cone penetration value on the X-axis shall be prepared. The best fitting straight line is then drawn. The moisture content corresponding to cone penetration of 20 mm shall be taken as the liquid limit of the soil and shall be expressed to the nearest first decimal place.

 Liquid Limit Graph (Mechanical Device Method):

Plastic limit test:

Object:

Determination of the plastic limit of the soils.

Apparatus:

Evaporating dish, spatula, glass plate, moisture containers, rod of 3 mm diameter, balance sensitive to 0.01 g and oven controlled at temperature 105 to 110 deg. C.

Procedure: 

About 20 g of dry pulverized soil passing 425 micron IS sieve is weighed. The soil is mixed thoroughly with distilled water in the evaporating dish till the soil paste is plastic enough to be easily moulded with fingers. A small ball is formed with the fingers and this is rolled between the fingers and the glass plate to a thread. The pressure just sufficient to roll into a thread of uniform diameter should be used. The rate of rolling should be between 80 to 90 strokes per minute counting a stroke as one complete motion of hand forward and back to the starting position again. The rolling is done till the diameter of the thread is 3 mm. Then the soil is kneaded together to a ball and rolled again to form thread. This process of alternate rolling and kneading is continued until the thread crumbles under pressure required for rolling and the soil can no longer be rolled into a  thread.

If the crumbling starts at diameter less than 3 mm, then moisture content is more than plastic limit and if the diameter is greater while crumbling starts, the moisture content is lower. By trial, the thread that starts crumbling at 3 mm diameter under normal rolling should be obtained and this should be immediately transferred to the moisture container, lid placed over it and weighed. The container is kept in the oven for about a day and dry weight found to determine the moisture content of the thread. The above process is repeated to get at least three consistent values of the plastic limit (PL or wp).

Calculations:

Plasticity Index (PI or Ip) = Liquid limit – Plastic limit.

 

       = LL - PL

       = wl - wp

 Toughness Index (TI or IT) = Ip / If

 Liquidity Index ( LI or Il) = (w – wp) / Ip

 where, ‘w’ is the natural moisture content of the soil.

 Consistency Index (CI or Io) = (wp – w) / Ip

 

7. COMPACTION TEST.

( IS : 2720 – PART – 7 & 8 )

INTRODUCTION:

Compaction of soil is mechanical processes by which the soils particles are constrain to be packed more closely together by reducing the air voids. Soil compaction causes decrease in air voids and consequently an increase in dry density. This may result in increase in shearing strength. The possibility of future settlement or compressibility decreases and also the tendency for subsequent changes in moisture content decreases.

Degree of compaction is usually measured quantitatively by dry density.

Increase in dry density of soil due to compaction mainly depends on two factors –

(i) the compacting moisture content and (ii) the amount of compaction.

For practically all soils it is found that with increase in the compaction moisture content, the dry density first increases and then decreases if compacted by any method. This indicates that under a

given compactive effort every soil has optimum moisture content (OMC) at which the soil attains maximum dry density (MDD). R.R.Proctor first recorded this fact in 1933.

The compaction test is divided into two parts (i) light compaction (IS: 2720 – Part - 7) and

(ii) heavy compaction (IS: 2720 – Part – 8).

Object:

To determine the compaction test by light / heavy compaction test method.

Apparatus:

a) Cylindrical mould of capacity 1000 cc, with an internal diameter of 10cm and height 12.73 cm or a mould of capacity 2250 cc, with an internal diameter of 15 cm and height of 12.73 cm. The mould is fitted with a detachable base plate and removable collar or extension of about 6 cm high.

b) For light compaction, a metal rammer having 5 cm diameter circular face, and weight 2.6 kg is used which has a free drop of 31 cm.

For heavy compaction, the rammer has 5 cm diameter circular face, but having weight 4.89 kg and free drop of 45 cm.

c) Steel straight edge having be leveled edge for trimming the top of the specimen.

d) Other accessories include moisture containers, balances of capacity 10 kg and 200 g ,

oven, sieves and mixing tools.

  

Procedure:

Preparation of samples:

For light compaction, about 20 kg of the representative soil is air-dried, mixed pulverized and sieved through 19 mm IS sieve. The fraction retained on 19 mm sieve is not used in this test. If there is note worthy proportion of materials retained on 19 mm sieve, allowance for larger size materials is made by replacing it by an equal weight of material passing 19 mm sieve and retained on 4.75 mm sieve.

 

For heavy compaction, about 45 kg of the representative soil is air-dried, mixed pulverized and sieved through 37.5 mm IS sieve. The fraction retained on 37.5 mm is not used in this test. If there is note worthy proportion of materials retained on 37.5 mm sieve, allowance for large size materials is made by replacing it by an equal weight of material passing 37.5 mm and retained on 4.75 mm sieve.

 For compacting the soil in the mould every time the required quantity will depend on the soil type, size of the mould, moisture content and amount of compaction. As a rough guidance, for each test 2.5 kg of soil may be taken for light compaction and 5.8 kg for heavy compaction. The estimated weight of water to be added to the soil every time may be measured with a graduated jar in cc.

Enough water is added to the specimen to bring the moisture content to about 7% less than the estimated OMC for sandy soils and 10% less for clayey soils. The processed soil is stored in an airtight container for about 18 to 20 hours to enable moisture to spread uniformly in the soil mass.

The mould with base plate fitted in is weighed. The process soil-water mixture is mixed thoroughly and divided into eight equal parts.

(i) For light compaction the wet soils is compacted into the mould in three equal layers, each layer being given 25 blows of the 2.6 kg hammer, if 10 cm diameter mould is used.

When the 15 cm diameter mould is used, 56 blows are given to each of the three layers by the 2.6 kg hammer.

(ii) For heavy compaction, the wet soil mix is compacted in the mould in five layers each layer being given 25 blows of 4.89 kg hammer when the 10 cm diameter of mould is used. When the 15 cm diameter mould is used, 56 blows are given to each of the five layers by 4.89 kg hammer.

The blows should be uniformly distributed over the surface of each layer. Each layer of the compacted soil is scored with a spatula before placing the soil for the succeeding layer. The amount of soil used should be just sufficient to fill the mould leaving about 5mm to be struck off on the top after compacting the final layer.

The collar is removed and the compacted soil is leveled off to the top of the mould by means of the straight edge. The mould and the soil is then weighed. The soil is then ejected out of the mould and cut in the middle and a representative sample is taken in airtight container from the cut surface. The moisture content of this representative specimen is determined by finding the wet weight, keeping in the oven at 1050 to 1100C and finding the dry weight the next day.

This procedure is repeated five to six times using fresh part of the soil specimen and after adding a higher water content than the preceding specimen every time so that the last compaction is carried out at moisture 7 to 10 percent higher than estimated optimum moisture content.

Calculations:

Let the weight of mould with moist compacted soil = W g

Weight of empty mould = Wm g

Volume of the mould = Vm cc

Moisture content = w %

Specific gravity of the soil = G

Wet density, ••m = ((W – Wm) / Vm  } g/cc

     

 

      •m                  (W – Wm)

Then dry density, •d =  --------  = ------------------      g/cc

     w                              w

      (1 +  ---- ) Vm(1 + ---- )

  100                          100

           

Vv                   •d

Porosity, n = 100 ---------% = (1 - -------) 100 %

V                     G •w

      G •w

Voids ratio, e = (-------   - 1)

       •d

Results:

Points are plotted with moisture content on the X-axis and dry density on the Y-axis and a smooth curve is drawn connecting the points. From this curve, the maximum dry density (MDD) is noted and the corresponding value of moisture content taken as optimum moisture content (OMC) of the soil.

 MDD & OMC Graph.

 

 

8. FIELD DENSITY TEST BY SAND REPLACEMENT METHOD.

( IS : 2720 – PART – 28 )

 

INTRODUCTION

The dry density of the compacted soil or pavement material is a common measure of the amount of the compaction achieved during the construction. Knowing the field density and field moisture content, the dry density is calculated. Therefore field density test is importance as a field control test for the compaction of soil or any other pavement layer.

There are several methods for the determination of field density of soils such as core cutter method, sand replacement method, rubber balloon method, heavy oil method etc.

One of the common methods of determining field density of fine-grained soils is core cutter method; but this method has a major limitation in the case of soils containing coarse-grained particles such as gravel, stones and aggregates. Under such circumstances, field density test by sand replacement method is advantageous, as the presence of coarsegrained particles will adversely affect the test results.

The basic principle of sand replacement method is to measure the in-situ volume of hole from which the material was excavated from the weight of sand with known density filling in the hole. The in-situ density of material is given by the weight of the excavated material divided by the in-situ volume.

Object:

To determination of field density by sand replacement method.

Apparatus:

a) Sand pouring cylinder equipment:

(i) Small pouring cylinder: suitable for fine and medium grained soils. This consists of a metal cylinder of capacity 3 liters, 100mm in diameter and 380 mm length with an inverted funnel or cone at one end and a shutter to open and close the entry of sand and a cap on the other end. Metal tray to excavate the hole with suitable shape and size.

Calibration container of the small pouring cylinder (size 100X150mm)

(ii) Large pouring cylinder: suitable for fine, medium and coarse grained soils. This consists a metal cylinder of capacity 16.5 liters, 200mm in diameter and 610mm length with all arrangements mentioned above. Calibration container size 200X250mm

(iii) Medium pouring cylinder: suitable for fine, medium and coarse grained soils. This cylinder with 150mm diameter and length 450mm. The calibration container size is 150X200mm.

b) Tools for leveling and excavating: Hand tools such as scraper with handle for leveling the surface; a dibber or an elongated trowel for digging and excavating the material.

c) Containers: Metal containers of any convenient size (about 150mm diameter and 200mm depth) with removable lid for collecting the excavated material.

d) Sand: Dry and clean test sand of uniform gradation, passing 1.0mm and retained 600- micron sieve.

e) Balance: A suitable balance of capacity 15 or 30 kg accuracy 1.0 g and necessary set of weights.

Procedure:

The test may be conducted in two stages: (i) calibration of apparatus and (ii) measurement of field density.

(i)            Calibration of apparatus: 

The determination of volume of the excavated hole is based on the weight of sand filling the hole and the cone and the density of the sand. Calibration of apparatus includes (a) determination of density of test sand used in the experiment under identical height and pouring conditions of the sand into the test hole and (b) determination of the weight of the sand occupying the cone of the sand-pouring cylinder.

Clean and dry test sand passing 1.0mm sieve and retained 600-micron sieve is collected in sufficient quantity required for at least three to four sets of tests. The top cap of the sand-pouring cylinder is removed, the shutter is closed, the cylinder is filled with dry test sand up to about 10mm from the top and the cap is replaced. The weight of the cylinder with the sand is determined accurate to one gram and is recorded = W1. In all the subsequent tests for calibration as well as for the field density tests, every time the sand is filled into the cylinder such that the initial weight of the cylinder with sand is exactly W1.

The sand pouring cylinder is placed over the calibration cylinder or one of the test holes already excavated, the shutter is opened and the sand equal to the volume of the calibration cylinder or the excavated test hole is allowed to flow out and the shutter is closed.

The sand pouring cylinder is now placed on a clean plane surface (glass or Perspex plate), the shutter is kept open till the sand fills up the cone fully and there is no visible movement of sand as seen from the top of the cylinder by removing the cap. The shutter is closed, the cylinder is removed and the sand which occupied the cone is carefully collected from the plate and weighed = W2.

The sand pouring cylinder is refilled with sand such that the initial weight is again W1.

Now the cylinder is placed centrally on the top of the calibration container and the shutter is opened. When the sand fills up the calibration container and the cone completely and there is no movement of sand, the shutter is closed and the sand pouring cylinder and the remaining sand is weighed = W3.

The above steps are repeated three times and the mean values of W2 and W3 are determined such that the mean value of the weight of sand required to fill the calibration container up to the level top can be determined.

The volume of the calibrating container, V is determined either by measuring the internal dimensions or by filling with water and weighing. From the weight of sand Wa and its volume V in the calibrating container, the density of sand, is determined.

(ii)          Measurement of field density: 

The site where the field density test is to be conducted is cleaned and leveled using a scraper for an area of about 450 mm square. The metal tray central hole is placed on the prepared surface. Using this central hole as pattern, the soil/material is excavated using a dibber or a trowel up to a required depth and the loose material removed is carefully collected in the metal container and is weighed = W. The sand-pouring cylinder is refilled with sand such that its weight is again W1. The metal tray with central hole is removed and the sand-pouring cylinder is placed centrally over the excavated hole. The shutter is opened till the sand fills the excavated hole and the cone completely and there is no further movement of sand in the cylinder. The shutter is closed and the cylinder is

weighed again = W4, so that the weight of sand filling the excavated hole alone = Wb

can be found.

The moisture content of the excavated soil, w% is determined by taking a sample of soil from it in a moisture content dish, weighing, drying in oven at 1100C and re-weighing.

Alternatively, the moisture content (w%) is determined by placing the entire excavated soil collected from the hole (of weight W) in the oven and finding its dry weight = Wd.

The above steps for the determination of the weights of excavated soil, the weight of the sand filling the hole and the weights of samples for the moisture content determination are repeated at least three times and the average values taken for the determination of field density (wet and dry) values.

Calculations and Results:

W1 = weight of sand pouring cylinder and sand filled up to 10mm from top edge, g

W2 = weight of sand in the cone, mean value, g

W3 = weight of cylinder and sand after pouring into the calibration container and cone, g

W4 = weight of cylinder and sand after pouring into the excavated hole and cone, g

Va = volume of the excavating container, cm3

W = weight of the soil from the excavated hole, g

Wd = oven dry weight of the soil excavated from the hole, g

w = moisture content of the soil, %

The weight of sand filling the calibrating container only = Wa = (W1 – W3 – W2), g

   

(i) Bulk density of sand, •s = Wa / Va , g/cm3

    

Weight of sand filling the excavated hole alone = Wb = (W1 – W4 – W2), g

Volume of sand filling the excavated hole alone = V = Wb / •s  , cm3

 (ii) In-situ bilk density of the wet excavated soil, ••= W / V , g/cm3

(iii) Moisture content of soil, w% = 100(W – Wd) /  Wd , %              

(iv) In-situ dry bulk density of the excavated soil, •d = = • Wd  / W = 100 •• / (100 + W), g/cm3

The results are reported as the average value of at least three sets of tests in the following:

(i) In-place wet density of soil in g/cm3, correct to second decimal place or in kg/m3, correct to nearest whole number.

(ii) In-place dry density of soil in g/cm3 or in kg/m3 (as above).

(iii) Moisture content of the soil in percent, correct to first decimal place.

 

9. CALIFORNIA BEARING RATIO TEST.

( IS : 2720 – PART – 16 )

INTRODUCTION:

 

The 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.

 

The CBR is a measure of resistance of a material to penetration of standard plunger under controlled density and moisture conditions. The test procedure should be strictly adhered if high degree of reproducibility is desired. The CBR test may be conducted in remoulded or undisturbed specimens in the laboratory. The test has been extensively investigated for field correlation of flexible pavement thickness requirement.

 

Briefly, the test consists of causing a cylindrical plunger of 50mm diameter to penetrate a pavement component material at 1.25mm/minute. The loads, for 2.5mm and 5mm are recorded. This load is expressed as a percentage of standard load value at a respective deformation level to obtain CBR value. The standard load values were obtained from the average of a large number of tests on different crushed stones and are given.

 

Penetration, mm	Standard Load, kg.	Unit standard load, kg/cm2
2.5	1370	70
5.0	2055	105
7.5	2630	134
10	3180	162
12.5	3600	183

 

Laboratory CBR test:

 

Apparatus:

a) Loading Machine: Any compression machine, which can operate at a constant rate of 1.25mm/minute, can be used. A metal penetration piston or plunger of diameter 50mm is attached to the loading machine.

 

b) Cylindrical moulds: Moulds of 150mm diameter and 175mm height provided with a collar of about 50mm length and detachable perforated base are used for this purpose. A spacer disc of 148mm diameter and 47.7mm thickness is used to obtain a specimen of exactly 127.3mm height.

 

c) Compaction Rammer: The material is usually compacted as specified for the work, either by dynamic compaction or by static compaction. The details for dynamic compaction suggested by the ISI are given.

 

Type of compaction	No.of layers	Hammer Wt. Kg	Fall, cm	No.of blows
Light compaction	3	2.6	31	56
Heavy compaction	5	4.89	45	56

 

 

d) Adjustable stem, perforated plate, tripod and dial gauge: The standard procedure requires that the soil sample before testing should be soaked in water to measure swelling. For this purpose the above listed accessories are required.

 

e) Annular weight: In order to simulate the effect of the overlaying pavement weight, annular weights each of 2.5 kg weight and 147mm diameter are placed on the top of the specimen, both at the time of soaking and testing the samples, as surcharge.

  

Procedure:

 

The CBR test may be performed either on undisturbed soil specimens obtained by fitting a cutting edge to the mould or on remoulded specimens. Remoulded soil specimens may be compacted either by static compaction or by dynamic compaction. When static compaction is adopted, the batch of soil is mixed with water to give the required moisture content; the correct weight of moist soil to obtain the desired density is placed in the mould and compaction is attained by pressing in the spacer disc using a compaction machine or jack. The preparation of soil specimens by dynamic compaction or ramming is more commonly adopted and is explained below.

About 45 kg of material is dried and sieved through 19mm sieve. If there is note worthy proportion of materials retained on 19mm sieve, allowance for larger size materials is made by replacing it by an equal weight of material passing 19mm sieve and retained on 4.75mm sieve. The optimum moisture content and maximum dry density of the soil are determined by adopting either light compaction or heavy compaction as per the requirement.

Each batch of soil (of at least 5.5 kg weight for granular soil and 4.5 to 5.0 kg weight for fine grained soils) is mixed with water up to the optimum moisture content or the field moisture content if specified so. The spacer disc is placed at the bottom of the mould over the base plate and a coarse filter paper is placed over the spacer disc. The moist soil sample is to be compacted over this in the mould by adopting either the light compaction or heavy compaction.

(i) For IS light compaction or Proctor compaction the soil to be compacted is divided into three equal parts; the soil is compacted in three equal layers, each of compacted thickness about 44mm by applying 56 evenly distributed blows of the 2.6 kg rammer.

(ii) For IS heavy compaction or the modified Proctor compaction, the soil is divided into five equal parts; the soil is compacted in five equal layers, each of compacted thickness about 26.5mm by applying 56 evenly distributed blows of the 4.89 kg rammer. After compacting the last layer, the collar is removed and the excess soil above the top of the mould is evenly trimmed off by means of the straight edge. It is important to see if the excess soil to be trimmed off while preparing each specimen is of thickness about 5.0mm; if not the weight of soil taken for compacting each specimen is suitably adjusted for the repeat tests so that the thickness of the excess layer to be trimmed off is about 5.0mm. Any hole that develops on the surface due to the removal of coarse particles during trimming may be patched with smaller size material. Three such compacted specimens are prepared for the CBR test. About 100g of soil samples are collected from the each mould for moisture content determination, from the trimmed off portion.

The clamps are removed and the mould with the compacted soil is lifted leaving below the perforated base plate and the spacer disc, which is removed. The mould with the compacted soil is weighed. A filter paper is placed on the perforated base plate, the mould with compacted soil is inverted and placed in position over the base plate (such that the top of the soil sample is now placed over the base plate) and the clamps of the base plate are tightened. Another filter paper is placed on the top surface of the sample and the perforated plate with adjustable stem is placed over it. Surcharge weights of 2.5 or 5.0 kg weight are placed over the perforated plate and the whole mould with the

weights is placed in a water tank for soaking such that water can enter the specimen both from the top and bottom. The swell measuring device consisting of the tripod and the dial gauge are placed on the top edge of the mould and the spindle of the dial gauge is placed touching the top of the adjustable stem of the perforated plate. The initial dial gauge reading is recorded and the test set up is kept undisturbed in the water tank to allow soaking of the soil specimen for four full days or 96 hours. The final dial gauge reading is noted to measure the expansion or swelling of the soil specimen due to soaking.

The swell measuring assembly is removed, the mould is taken out of the water tank and the sample is allowed to drain in a vertical position for 15 minutes. The surcharge weights, the perforated plate with stem and the filter paper are removed. The mould with the soil sample is removed from the base plate and is weighed again to determine the weight of water absorption.

The mould with the specimen is clamped over the base plate and the same surcharge weights are placed on the specimen centrally such that the penetration test could be conducted. The mould with base plate is placed under the penetration plunger of the loading machine. The penetration plunger is seated at the center of the specimen and is brought in contact with the top surface of the soil sample by applying a seating load of 4.0 kg. The dial gauge for measuring the penetration values of the plunger is fitted in position. The dial gauge of the proving ring (for load readings) and the penetration dial gauge are set to zero. The load is applied through the penetration plunger at a uniform rate of 1.25 mm/min. The load readings are recorded at penetration readings of 0.0, 0.5,

1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10.0 and 12.5 mm. In case the load readings start decreasing before 12.5mm penetration, the maximum load value and the corresponding penetration value are recorded. After the final reading, the load is released and the mouldis removed from the loading machine. The proving ring calibration factor is noted so that the load dial values can be converted into load in kg. About 50g of soil is collected from the top three cm depth of the soil sample for the determination of moisture content.

Calculations:

The swelling or expansion ratio is calculated from the observations during the swelling test using the formula:

100 (df – di)

Expansion ratio or swelling =        ------------------

h

 

Where,           df = final dial gauge reading after soaking, mm

di = initial dial gauge reading before soaking, mm

h = initial height of the specimen (127.3 mm), mm

The load values noted for each penetration level are divided by the area of the loading plunger (19.635cm2) to obtain the pressure or unit load values on the loading plunger.

The load-penetration curve is then plotted in natural scale for each specimen. If the curve is uniformly convex upwards, no correction is needed. In case there is a reverse curve or the initial portion of the curve is concave upwards, necessity of a correction is indicated.

A tangent is drawn from the steepest point on the curve to intersect the base at point, which is the corrected origin corresponding to zero penetration. The unit load values corresponding to 2.5 and 5.0 mm penetration values are found from the graph.

The CBR value is calculated from the formula:

 

Unit load carried by soil sample at defined penetration level

CBR, % =       ------------------------------------------------------------------------------------------------ X 100

Unit load carried by standard crushed stones at above penetration level

 

Results:

The CBR values at 2.5mm and 5.0mm penetrations are calculated for each specimen from the corresponding graphs. Generally the CBR value at 2.5mm penetration is higher and this value is adopted. However if higher CBR value is obtained at 5.0mm penetration, the test is to be repeated to verify the results; if the value at 5.0mm is again higher, this is adopted as the CBR value of the soil sample. The average CBR values of three specimens are reported to the first decimal place.

 

Field CBR Test.

 

Apparatus:

 

A reaction load like a truck, tractor or truss is required for applying the load by means of a mechanical screw jack. The other equipment needed are 5 cm diameter loading plunger, extension rods, jacks, proving ring assembly, dial gauge, datum frame, annular surcharge plate 25 cm in diameter and 5 kg in weight, with a central hole and slot width 5.3 cm and two circular slotted weights of 10 kg and diameter about 25 cm with central hole and slot width of 5.3 cm.

 

Procedure:

A circular area of about 30 cm in diameter is trimmed and leveled. Particular care should be taken at the center where the plunger is to be seated. The surcharge load of 15 kg is placed on this surface and the plunger is seated properly. The dial gauge to measure the penetration is attached to the plunger from an independent datum frame. A seating load of 4 kg is applied and the load and penetration dials are set to zero.

The load is applied to the plunger by means of the jack such that the rate of penetration is approximately 1.25 mm/minute. The load readings are noted for at penetrations 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10.0 and 12.5 mm. The load is released and moisture content specimen is taken from underneath the plunger.

Calculations:

The load – penetration curve is plotted, and the CBR value is calculated as in the case of laboratory CBR.

CBR Graph:

 

 

 

10. SHEAR TEST BY TRIAXIAL METHOD.

( IS : 2720 – PART – 12 )

 

INTRODUCTION:

Shear tests are generally carried out on small soil samples in the laboratory to evaluate the strength properties of the element in the soil mass. The strength parameters, namely the cohesion and angle of shearing resistance are usually found from these tests. The two methods of shear tests commonly used are the direct shear test and the triaxial test.

 

Apparatus:

The triaxial machine consists of a pressure cell assembly and equipment for loading and measuring the load and deformation.

Triaxial pressure cell: Cylindrical soil specimen inserted in a thin rubber membrane and kept sealed to prevent the entry of lateral fluid, can be placed in position in the cell. There is provision to apply radial fluid pressure and vertical stress through a piston. There is also facility to allow or prevent drainage of specimen during the application stresses.

A pressure gauge may be used to measure the fluid pressure in the cell.

Loading equipment: Usually strain controlled equipment is used; stress controlled equipment is also used in some tests. A proving ring assembly may measure the vertical load applied on the piston. A dial gauge attached to the piston measures the deformation of specimen.

Procedure:

Preparation of specimen:

Either undisturbed or remoulded specimens may be prepared as desired. Larger size of undisturbed soil sample may be taken and trimmed to desired size. But undisturbed soil sample can be prepared only from soils having sufficient cohesion. Remoulded samples of cohesive soils may be prepared either by compacting first in large mould and by pressing hollow cutters or in constant volume moulds. Special care is needed while preparing specimens of cohesion less soil, in special mould afterplacing the membrane in proper position. The cylindrical specimens usually have height to diameter ratio equal to two; this ratio does not however exceed 2.5.

Test type:

Three types of triaxial tests may be performed in partially or fully saturated specimens. These are (i) undrained or quick test,

(ii) consolidated – undrained test and

(iii) drained or slow test.

In the undrained or quick test the out let valve is closed and no drainage is allowed from the specimen during the test, from the time of application of lateral pressure •3 till the specimen fails under gradually increasing vertical load. In the consolidated undrained test, the drainage valve is kept open and the specimen is allowed to fully consolidate under the applied lateral pressure •3; but no further drainage is allowed during the application of the vertical load, till failure.

In the drained or slow test the drainage is allowed during all stages of testing. First the specimen is allowed to fully consolidate under the applied lateral pressure •3 and later the vertical load is also applied in such a way that there is enough time for the drainage of pore water pressure developed from time to time.

There are two methods of applying the lateral or confining pressure. Usually the lateral pressure •3 is maintained constant throughout the test. But in some studies the volume of the specimen is maintained constant by adjusting the lateral pressure.

Procedure:

The specimen enveloped properly in the membrane is kept in the triaxial cell and a desired lateral pressure ?3 is applied. Then the vertical load is increased till the specimenfails noting the vertical deformation and load readings at desired intervals. The experiment is repeated for various other values of lateral pressure. To find the values of cohesion and angle of internal friction, tests should be carried out with at least two or three different lateral pressure values. Soils may be tested with lateral pressures of 0, 0.75 and 1.5 kg/cm2.

Calculations:

The triaxial test specimen is subjected to the all round pressure equal to the lateral pressure •3 and the applied vertical stress or deviator stress •d such that the total vertical stress •1 = •d••+ ••3. Mohr stress circles are plotted at normal stress intercepts •3 and • or with diameters equal to deviator stresses. Mohr rupture envelope is then obtained by drawing a tangent to the circles. The intercept of this line with Y-axis represents the cohesion (C) and the inclination with X-axis represents the angle of internal friction (•) of the soil.

 

Correction for area of cross section: It is necessary to correct the deviator stress values for the increased area of cross section due to loading. Assuming that the volume of specimen remains constant and the area of cross section of the specimen increases uniformly, the corrected value of deviator stress •d is calculated from the relation:

              

•d = P1    /  A0     [   1 - • /  l0  ]

                

 

Where,           P1 = applied load.

A0 = original area of cross section.

••••••••••••••••= deformation of specimen.

l0 = original length of specimen.

The shearing resistance is found the following equation:

S = C + • tan •

Mohr’s Envelope from Triaxial Test.

 

  

11. SAND EQUIVALENT TEST.

( IS : 2720 – PART – 37 )

INTRODUCTION:

This test is intended to serve as a rapid field test to show the relative proportions of fine dust or clay like material in soils or graded aggregates.

Apparatus:

1) A graduated plastic cylinder, rubber stopper, irrigator tube, weighted foot assembly, and siphon assembly, all confirming to their respective specifications and dimensions. Fit the siphon assembly to a 4 liters bottle of working calcium chloride solution placed on a shelf 915 +/- 25mm above the work surface. In lieu of the specified 4liter bottle, a glass or plastic vat having a larger capacity may be used providing the liquid level of the working solution is maintained between 915 to 1175mm above the work surface.

2) A 85 ml tinned box approximately 57mm in diameter, with gill style cover and having a capacity of 85 +/- 5ml.

3) A wide mouth funnel approximately 100mm in diameter at the mouth.

4) A clock or watch reading in minutes and seconds.

5) A mechanical shaker having a throw of 203.2 +/- 1.02mm and operating at 175 +/- 2 cycles per minute.

6) Dissolve the calcium chloride in 1.89 liters of distilled water. Cool the solution, then filter and add the glycerin and formaldehyde to the filtered solution, mix well, and dilute to 3.79 liters with distilled or dematerialized water.

7) Prepare the working calcium chloride by diluting one measuring tin full 85 +/- 5ml of the stock calcium chloride solution 3.79 liters with water. Use distilled water for the normal preparation of the working solution.

Sample preparation:

The sand equivalent test shall be performed on soils or graded aggregate materials passing the 4.75mm sieve. All aggregates of fine-grained soil material shall be pulverized to pass the 4.75mm sieve, and all fines shall be cleaned from the particles retained on the 4.75mm sieve and included with the material passing the 4.75mm sieve. Split enough of the original sample to yield slightly more than 85ml tin measures of material passing the 4.75mm sieve. Use extreme care to obtain a truly representative portion of the original sample.

Procedure:

Siphon 101.6 +/- 2.5ml of working calcium chloride solution into the paste cylinder. Pour the prepared test sample from the measuring tin into the plastic cylinder using the funnel to avoid spillage. Tap the bottom of the cylinder sharply on the heel of the hand several times to release air bubbles and to promote thorough wetting of the sample. Allow the wetted sample to stand undisturbed for 10 minutes. At the end of the 10-minute soaking period, stopper the cylinder, then loosen the material from the bottom by partially inverting the cylinder and shaking it simultaneously. Hold the cylinder in a horizontal position and shake it vigorously in a horizontal linear motion from end to end. Shake the cylinder 90 cycles in approximately 30 seconds using a throw of 229 +/- 25mm. A cycle is defined as a complete back and front motion. To properly shake the cylinder at this speed, it will be necessary for the operator to shake with the forearms only, relaxing the

body and shoulders.

Allow the cylinder and contents to stand undisturbed to 20 minutes, read the level of the top of the clay suspension. This is referred to as the ‘clay reading’. After the clay reading has been taken, the ‘sand reading’ shall be obtained by the following method:

When using the weighted foot assembly having the sand indicator on the rod of the assembly, place the assembly over the cylinder and gently lower the assembly towards the sand. Do not allow the indicator to hit the mouth of the cylinder as the assembly is being lowered. As the weighted foot comes to rest on the sand, tip the assembly toward the graduations on the cylinder until the indicator touches the inside of the cylinder.

Subtract 254mm from the level indicated by the extreme top edge of the indicator and record this value as the ‘sand reading’.

Calculations:

Sand equivalent (SE) to the nearest 0.1 using the following formula: 

SE = (Sand Reading X 100 ) / Clay Reading

 12. BEARING CAPACITY OF SOIL BY PLATE LOAD BEARING TEST.

( IS : 1888 – 1982 )

INTRODUCTION:

This is the method of conducting the load test on soils and the 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 and instruments to measure the applied loads and resulting settlement.

a) 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, 45, 30 and 22.5 cm dia.) used as stiffeners.

b) 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. The load applied may be measured either by a proving ring and dial gauge assembly or a pressure gauge connected to the output end of the hydraulic jack.

c) 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 site is prepared and loose material is removed so that the 75 cm diameter plate rests horizontally in full contact with the soil sub-grade. If the modulus of sub-grade reaction of natural ground is needed, the topsoil may be removed up to a depth of about 20 cm before testing.

The plate is seated accurately and then a seating load equivalent to a pressure of 0.07 kg/cm2 (320 kg for 75 cm diameter plate) is applied and released after a few seconds. The settlement dial readings are now noted corresponding to zero load. A load is applied by means of the jack, sufficient to cause an average settlement of about 0.25 mm. When there is no perceptible increase in settlement or when the rate of settlement is less than 0.025 mm per minute (in the case of soils with high moisture content or in clayey soils) the load dial reading and the settlement dial readings are noted. The average of the three (or four) settlement dial readings is taken as the average settlement of the plate corresponding to the applied load.

The load is then increased till the average settlement increase to a further amount of about 0.25 mm, and the load and average settlement readings are noted as before. The procedure is repeated till the settlement is about 1.75 mm or more.

Bearing pressure-settlement curve:

 

 

Calculations:

A graph is plotted with the mean settlement versus bearing pressure (load per unit area) as shown in above. The pressure ‘p’ (kg/cm2) corresponding to a settlement ? = 0.125 cm is obtained from the graph. The modulus of sub grade reaction ‘K’ is calculated from the relation.

K = ( p / 0.125 )  kg/cm2/cm or kg/cm3.