SOIL CLASSIFICATION AND SOIL TESTING (Part - 1)

CONTENT

SL NO	NAME OF TEST
	INTRODUCTION
1	CLASSIFICATION OF SOILS.
2	GRAIN SIZE ANALYSIS
3	SPECIFIC GRAVITY TEST FOR SOILS.
4	MOISTURE CONTENT TEST.
5	FREE SWELL INDEX TEST.

INTRODUCTION:

 Soil is very essential material for highway constructions.

In view of the wide diversity in soil type, it is desirable to classify the sub grade soil into groups possessing similar physical properties. Many methods have been in use for this purpose. Soils are normally classified on the basis of simple laboratory tests such as grain size analysis and  consistency tests.

 Soil compaction is important phenomenon in highway construction as compacted sub grade improves the load supporting ability of pavement; in turn resulting in decreased pavement thickness requirement. Compaction of earth embankments would result in decreased settlement. Thus the behavior of soil sub grade material could be considerably improved by adequate compaction under controlled conditions. The laboratory compaction test results are useful in specifying the optimum moisture content at which a soil should be compacted and the dry density that should be aimed at the construction site. The in-situ density of prepared sub grade as well as other pavement layers has to be determined by a field density test for checking the compaction requirements and as a field control test for compaction.

There are a number of tests for measuring soil strength; some of them give the strength

parameters of the soil, other methods are empirical and give only arbitrary strength values. The types of the strength tests may be classified as shear test, bearing tests and penetration tests. The triaxial test results are useful to find the strength parameters, viz: cohesion and angle internal friction and modulus deformation of soils. The California Bearing Ratio test is essentially a penetration test, which is carried out either in the laboratory or in the field. This test is suitable for the evaluation of strength of soil and aggregates. The method has an important place among highway material testing programme, as it has been extensively correlated with flexible pavement design and performance. North Dakota Cone Test is another penetration test, which may also be

carried out either in the laboratory or on in-situ soil in the field, but its use is restricted to fine grained soils free from coarse particles. Plate bearing test is carried out either on subgrade to find the modulus of subgrade reaction or on a pavement component layer for pavement evaluation.

 There are several soils, which are unsuitable as highway materials, since they cannot be used as such in the base course, sub-base or the subgrade. The strength and durability characteristics of these soils can be improved to the desired extent by adopting a stabilization technique. One of the widely used methods of stabilization is soil-cement and soil-lime, which are applicable to a fairly wide range of soil types. The cement and lime stabilization soil can be used in sub-base and base course layers of pavement.

 

1.CLASSIFICATION OF SOILS.

( IS : 1498 – 1970 )

 INTRODUCTION:

The purpose of soil classification is to arrange various types of soils into groups according to their engineering properties and various other characteristics. From engineering point of view, the classification may be done with the objective of finding the suitability of the soil for construction of highway foundations.

 For general engineering purposes, soils may be classified by the following systems.

 i) Particle size classification.

ii) Textural classification.

iii) Highway Research Board (HRB) classification.

iv) Unified soil classification and IS classification system.

i) Particle size classification: In this system, soils are arranged to the grain size. Terms such as gravel, sand, silt and clay are used to indicate grain sizes. There are various grain size  classifications in use, but the more commonly used systems are;

      (i)U.S.Bureau of soil and Public Road Administration (PRA) system of United States.

(ii) International soil classification, proposed at the International Soil Congress at  ashington,D.C

(iii)  Massachusetts Institute of Technology (MIT) classification and

(iv) Indian Standard classification.

 

Indian standard classification:

 

> 300mm                            - Boulders

300 – 80mm                      - Cobble

80 – 20mm                        - Coarse Gravel

20 – 4.75mm                     - Fine Gravel

4.75 – 2mm                       - Coarse Sand

2mm – 425mic                  - Medium Sand

425mic. – 75mic.              - Fine Sand

75mic – 2mic                     - Silt

< 2 micron                         - Clay.

 

ii) Textural classification: Soils occurring in nature are composed of different percentage of  sand, silt and clay size particles. Soil classification of composite soils exclusively based on the particle size distribution is known as textural classification. The classification is based on the percentages sand, silt and clay sizes making up the soil.

To use the chart, for the given percentages of the three constituents forming a soil, lines are drawn parallel to the three sides of the equilateral triangle; the three lines intersect at one point. That point in the sector designated as the classification of that soil.

 Textural classification chart:

 

 iii) Highway Research Board (HRB) classification: This system is based on both the particle-size composition as well as the plasticity characteristics. This system is mostly used for pavement construction. Soils are divided into 7 primary groups, designated as A-1, A-2… A-7. Group A-1 is divided into two sub-groups and group A-2 into four subgroups.

 A characteristic ‘group index’ is used to describe the performance of the soils when used for pavement construction.

 The group index of a soil depends upon

(i)            the amount of material passing the 75 micron IS sieve,

(ii)          the liquid limit, and

(iii)         (iii) the plastic limit, and is given by the following equation:

 Group index = 0.2 a + 0.005 ac + 0.01 bd

 Where, a = that portion of percentage passing 75 micron sieve greater than 35 and not exceeding 75 expressed as a whole number (0 to 40).

b = that portion of percentage passing 75 micron sieve greater than 15 and not exceeding 75 expressed as a whole number (0 to 40).

c = that portion of the numerical liquid limit greater than 40 and not exceeding 60 expressed as positive whole number (0 to 20).

d = that portion of the numerical plasticity index greater than 10 and not exceeding 30 expressed as a positive whole number (0 to 20).

 HRB – Classification of soils :

 

iv) Unified soil classification and Indian standard classification: The system is based on both grain size and plasticity properties of the soil.

Soils are broadly divided into three divisions

i) Coarse grained soils: In these soils, more than half the total material by weight is larger than 75 micron IS sievs size.

Coarse-grained soils are further divided into two sub-divisions:

a) Gravels (G): In these soils, more than half the coarse fraction is larger than 4.75mm IS sieve size. This sub-division includes gravels and gravelly soils, and is designated by symbol ‘G’.

 b) Sands (S): In these soils, more than half the coarse fraction is smaller than 4.75mm IS

sieve size. This sub-division includes sands and sandy soils, and is designated by symbol ‘S’.

Each of the above sub-divisions are further sub-divided into four groups depending upon grading and inclusion of other materials:

 W : Well graded, clean.

 C : Well graded with excellent clay binder.

 P : Poorly graded, fairly clean.

 M : Containing fine materials not covered in other groups.

 These symbols used in combination designate the type of coarse-grained soils. For example, GC means clayey gravels.

 ii) Fine grained soils: In these soils, more than half the material by weight is smaller than 75 micron IS sieve size.

 Fine-grained soils further divided into three sub-divisions:

 a) Inorganic silt and very fine sands – designated by ‘M’.

 b) Inorganic clays – designated by ‘C’.

 c) Organic silts and clays, and organic matter – designated by ‘O’.

 The fine-grained soils are further divided into the following groups on the basis of the liquid limit.

i) Silts and clays of low compressibility, having a liquid limit less than 35, and represented by symbol ‘L’.

ii) Silts and clays of medium compressibility, having a liquid limit greater than 35 and less than 50, and represented by symbol ‘I’.

iii) Silts and clays of high compressibility, having a liquid limit greater than 50, and represented by a symbol ‘H’.

Combination of these symbols indicates the type of fine-grained soil. For example, ML means inorganic silt with low to medium compressibility.

Laboratory classification of fine-grained soil is done with the help of plasticity chart. The A-line, dividing inorganic clay from silt and organic soil has the following equation:

 

Ip = 0.73 (wL – 20)

 Where,         Ip = Plasticity Index.

WL = Liquid Limit.

 Plasticity chart:

  

iii) Highly organic soils and other miscellaneous soil materials:

 These soils contain large percentages of fibrous organic matter, such as peat, and the particles of decomposed vegetation.

 IS Soil classification: Laboratory classification criteria for Coarse-grained soils

 

 

2.GRAIN SIZE ANALYSIS.

( IS : 2720 – PART – 4 )

 INTRODUCTION:

 Most of the methods for soil identification and classification are based on certain physical properties of the soils. The commonly used properties for the classification are the grain size distribution, liquid limit and plasticity index. These properties have also been used in empirical design methods for flexible pavements, and in deciding the suitability of sub grade soils.

Grain size analysis also known as mechanical analysis of soils is the determination of the percent of individual grain sizes present in the sample.

 The mechanical analysis consists of two parts:

 (i) the determination of the amount and proportion of coarse material by the use of sieves.

 (ii) the analysis for the fine grained fraction by sedimentation method.

The sieve analysis is a simple test consisting of sieving a measured quantity of material through successively smaller sieves. The weight retained on each sieve is expressed as a percentage of the total sample. The sedimentation principle has been used for finding the grain size distribution of fine soil fraction; two methods are commonly used (i) Pipette method and (ii) Hydrometer method.

The grain size distribution of soil particles of size greater than 75 micron is determined by sieving the soil on a set of sieves of decreasing sieve opening placed one below the other and separating out the different size ranges. Two methods of sieve analysis are as follows:

(i) wet sieving applicable to all soils and

(ii) dry sieving applicable only to soils, which have negligible proportion of clay and silt.

The soils received from the field is divided into two parts: one, the fraction retained on 2mm sieve and the other passing 2mm sieve. The sieve analysis also may be carried out separately for these two fractions. The fraction retained on 2mm sieve may be subjected to dry sieving using bigger sieves and that passing 2mm sieve may be subjected to wet sieving; however if this fraction consists of single grained soil with negligible fines passing 0.075mm size, dry sieving may be carried out.

Apparatus:

Various apparatus include set of standard sieves of different sieve sizes, balance, rubber

covered pestle and mortar, oven, riffle and sieves shaker.

 

Procedure:

(a) For the fraction retained on 2.0mm sieve:

Sufficient quantity of the dry soil retained on 2.0mm sieve is weighed out. The quantity of sample taken may be increased when the maximum size of particles is higher. The sample is separated into various fractions by sieving through the set of sieves of sizes 100, 63, 20, 6, 4.75 and 2 mm IS

sieves. Additional sieve size may also be introduced if necessary. After initial sieving, the material retained on each sieve is collected, the lumps broken down using mortar and rubber covered pestle and is re-sieved thus the soil fraction retained on each sieve is carefully collected and weighed.

 (b) For the fraction passing 2.0mm sieve and retained on 0.075mm sieve:

Dry sieving may be done in the case of soils which are cohesion less, single grained and without

lumps. Rifling or quartering method takes the required quantity of soil sample, dried in oven at 105 to 110 deg.C and is subjected to dry sieve analysis using a set of sieves with sieve openings 2.0, 0.6, 0.425, 0.15 and 0.075 mm, pan and lid, additional sieves may be used or any of the sieves removed, depending upon the requirement of the test. The material retained on each sieve and on the pan are separately collected and weighed.

 Wet sieving may be adopted in the case of clayey or cohesive soils. Required quantity of sample taken by riffling is weighed. The sample is spread in a tray or bucket and covered with water. In case of soils having fractions that are likely to flocculate a dispersing agent like sodium hexametaphosphate (2.0g) or sodium hydroxide (1.0g) and sodium carbonate (1.0g) per liter of water may be added to the water. The mix is stirred and left for soaking. The soaked soil specimen is placed over the set of sieves of sizes with the finest sieve and pan at the bottom and washed thoroughly. Washing is continued till the water passing each sieve is substantially clean. The  raction of each sieve is emptied carefully without loss of material in separate trays, oven dried at 105 to 110 deg.C and each fraction weighed separately.

Calculations:

The weight of dry soil fractions retained on each sieve is calculated as a percentage of the

total dry weight of the sample taken.

Results:

The results are plotted on a semi-logarithmic graph with the grain size or sieve size on the X-axis in log. scale and the percentage finer of each sieve on the Y-axis in ordinary scale.

The smooth curve joining the points thus obtained is known as the particle size distribution curve or diagram.

 Uniformity coefficient of soil, Cu = D60 / D10

 Coefficient of curvature, Cc = (D30)2 / (D10 X D60)

 Where, D60, D30 and D10 are particle sizes corresponding to 60, 30 and 10 percent finer.

(c) For the fraction passing 0.075mm sieve: Two methods are in use based on sedimentation principle that the larger grains settle more rapidly than the smaller ones.

The Stoke’s law is made use of according to which the velocity of settlement of spherical particles is proportional to the square of their diameters. Thus if the depth and the duration of settlement are known, the velocity and hence the diameter of particles at that depth can be estimated. The percentage of particles finer than this diameter should be found using any one of the two methods viz; (i) Pipette method and (ii) Hydrometer method.

 

Hydrometer method.

Apparatus:

a) Density hydrometer confirming to IS: 3104-1965 –(Range 0.995 – 1.030).

b) Two glass-measuring cylinders of 1000 ml capacity with ground glass or rubber stoppers about 7 cm diameter and 33 cm high marked at 1000 ml volume.

c) Thermometer to cover the range 0 to 50 deg. C, accurate to 0.50 deg.C.

d) Water bath or constant temperature room

e) Stirring apparatus

f) 75 micron sieve.

g) Balance accurate to 0.01g

h) Stop watch

i) Wash bottles containing distilled water

j) Glass rod, about 15 to 20 cm long and 4 to 5 mm in diameter

k) Reagents: Hydrogen peroxide, Hydrochloric acid N solution and Sodium hexametaphosphate.

l) Conical flask of 1000ml capacity

m) Funnel, filter paper, measuring cylinder of 100ml capacity and blue litmus papers.

Procedure:

(A) Calibration of Hydrometer:

1.Determination of volume of the hydrometer bulb (Vh): Pour about 800ml of distilled water in the 1000ml-measuring cylinder and note the reading at the water level. Immerse the hydrometer in water and note the water reading. The difference between the two readings is recorded as the volume of the hydrometer bulb plus the volume of that part of the stem, which is submerged. For practical purposes, the error due to the inclusion of this stem volume may be neglected. Alternatively, weigh the hydrometer to the nearest 0.2g. This weight in grams is recorded as the volume of the hydrometer in ml. This includes the volume of the bulb plus the volume of the stem. For practical purposes the error due to the inclusion of the stem may be neglected.

2. In order to find the area of cross-section (A) of the measuring cylinder in which the hydrometer is to be used, measure the distance, in cm, between two graduations of the cylinder. The cross-section area (A) is then equal to the volume included between the two graduations divided by the distance between them.

 3. Measure the distance (h) from the neck to the bottom of the bulb, and record it as the

height of the bulb.

 4. With the help of an accurate scale, measure the height (H) between the necks of the

hydrometer to each of the other major calibration marks (Rh).

 5. Calculate the effective depth (He) corresponding to each of the major calibration marks

(or hydrometer readings, Rh) by the following expression:

 

                           

He = H +  (h/2) x ( h -  Vh /A)                                

6. Draw a calibration curve between He and Rh, which may be used for finding the effective depth (He) corresponding to hydrometer readings (Rh) obtained during the test.

7. Meniscus correction (Cm) : Insert the hydrometer in the measuring cylinder containing about 700ml of water. Take the readings of the hydrometer at the top and bottom of the meniscus. The difference between two readings is taken as the meniscus correction (Cm), which is a constant for hydrometer. During the actual sedimentation test, the readings should be taken at the bottom of the meniscus but since the soil suspension is opaque, readings are taken at the top of meniscus. The meniscus correction is always positive.

(B) Pre- treatment of soil:

1. Weigh accurately (to 0.01g) 50 to 100 g of oven dried soil sample (Wd) passing the 0.075mm IS sieve. If the percentage of soluble salts is more than one percent, the soil should be washed with water before further treatment, taking care to see that the soil particles are not lost.

2. Add 150ml of hydrogen peroxide to the soil sample placed in a wide mouth conical flask and stir it gently for few minutes with a glass rod. Cover the flask with glass and leave it to stand overnight.

3. Next morning, the mixture in the conical flask is gently heated in an evaporating dish, stirring the contents periodically. Reduce the volume to about 50ml by boiling. With very organic soils additional peroxide may be required to complete the oxidation.

4. If the soil contains insoluble calcium compounds, add about 50ml of hydrochloric acid to the  cooled mixture of soil obtained in step 3. The solution is stirred with a glass rod for a few minutes and allowed to stand for one hour or for longer periods, if necessary. The solution will have an acid reaction to litmus.

5. Filter the mixture and wash it with warm water until the filtrate shows no acid reaction to litmus. Transfer the damp soil on the filter paper and funnel to the evaporating dish using a jet of distilled water. Place the dish and its contents to the oven. Take the weight (Wb) of the oven-dried soil remaining after pre-treatment and find the loss of weight due to pre-treatment.

 (C) Dispersion of soil:

1. To the oven-dried soil, add 100ml of sodium hexametaphosphate solution and warm the mixture gently for about 10 minutes. Transfer the mixture to the cup of the mechanical mixer using a jet of distilled water, and stir it well for about 15 minutes. The sodium hexametaphosphate solution is prepared by dissolving 33 g of sodium hexametaphosphate and 7 grams of sodium carbonate in distilled water to make one liter of solution. This solution is unsuitable and should be freshly prepared approximately once in a month.

2. Transfer the soil suspension to the 75 micron IS sieve placed on a receiver and washes the soil on this sieve using jet of distilled water from a wash bottle. The amount of distilled water used during this operation may be about 500ml.

3. Transfer the soil suspension passing the 75-micron IS sieve to the 1000ml-measuring cylinder, and adds more water to make the volume to exactly 1000ml in the cylinder.

4. Collect he material retained on 75-micron sieve and put it in the oven for drying.

Determination the dry weight of soil retained on 75-micron sieve.

(D) Sedimentation test with hydrometer:

1. Insert a rubber bung or any other suitable cover on the top of the 1000ml-measuring cylinder containing the soil suspension and shake it vigorously end over end. Stop shaking and allow it to stand. Immediately, start the stopwatch, and remove the top cover from the cylinder.

2. Immerse the hydrometer gently to a depth slightly below its floating position and then allow it to float freely. Take the hydrometer readings after periods of 0.5, 1, 2 and 4 minutes. Take out the hydrometer, rinse it with distilled water and allow it to stand in a jar containing distilled water at the same temperature as that of the test cylinder.

3. The hydrometer is re-inserted in the suspension and readings are taken after periods of

8, 15 and 30 minutes; 1, 2 and 4 hours after shaking. The hydrometer should be removed,

rinsed and placed in the distilled water after each reading. After the end of 4 hours,

readings should be taken once or twice within 24 hours.

4. Composite correction (C): In order to determine the composite correction, put 100ml of dispersing agent solution in another 1000ml measuring cylinder and make it to 1000ml by adding distilled water. The cylinder should be maintained at the same temperature as that of the test cylinder containing soil specimen. Insert the hydrometer in this comparison cylinder containing distilled water and the dispersing agent and take the reading corresponding to the top of the meniscus. The negative of the hydrometer reading.

So obtained gives the composite correction (C). The composite correction is found before

the start of the test, and also at every time intervals of 30 minutes, 1 hour, 2 hours and 4

hours after the beginning of the test, and afterwards, just after each hydrometer reading is

taken in test cylinder.

5. The temperature of the suspension should be observed and recorded once during the

first 15 minutes and then after every subsequent reading.

Calculations:

(1) The loss in weight in pre-treatment of the soil in percentage is calculated from the

following expression: 

                     P = (1 - (Wb /  Wd )} x 100 

 Where,         P = loss in weight in percentage

Wd = weight of dry soil sample taken from the soil passing 2mm Sieve

Wb = weight of the soil after pre-treatment

(2) The diameter of the particle in suspension at any sampling time t is calculated from:

 

-5                      0.5

D = 10   M ( He / t )

Where,           M = poise constant factor

He = effective depth of the hydrometer

t = elapsed time, minutes

(3) The percentage finer N/ based on the weight Wd is calculated from:

                     N / ={100 G / Wd ( G – 1 )} x   R

 Where,         N/ = percentage finer, based on the weight of dry soil sample Wd

Wd = weight of dry soil sample taken from the soil sample passing 2mm sieve.

G = specific gravity of the soil passing 75 micron sieve.

R = corrected hydrometer reading

R = Rh / + C

                     Rh = Rh / + Cm

Where,          Rh/ = observed hydrometer reading

Rh = hydrometer reading, corrected for meniscus correction

(4) The percentage finer (N) based on the total weight of dry soil sample (W) is obtained from the relation:

 

 N = N/ X (W/ / W)

 Where,           W/ = cumulative weight passing 2mm sieve.

Values of Factor ‘M’

 

 

 3. SPECIFIC GRAVITY TEST FOR SOILS.

( IS : 2720 – PART – 3 )

Object:

 To determine the specific gravity of soil fraction passing 4.75 mm sieve by density bottle.

 Apparatus:

1) Density bottle of 50ml / 100ml capacity.

 2) Balance sensitive to 0.01g.

 3) Wash bottle with desired distilled water

 4) Vacuum source

 Procedure:

To clean and dry the density bottle, wash it thoroughly with distilled water and allow it to drain. Weigh the empty cleaned bottle (W1) accurate to 0.01g with its stopper. Take about 10 to 20 grams of oven dried soil sample; find the weight (W2) of the bottle and the soil, with the stopper. Put about 10ml of deaired distilled water in the bottle, so that the soil is fully soaked. Leave it for a period of 2 to 10 hours. Add more distilled water so that the bottle is about half full. Remove the entrapped air by subjecting the contents to a partial vacuum, then find out the weight (W3). Clean the bottle thoroughly and fill it with distilled water and weighed (W4). Temperature should be maintained 27 deg.C through out the test.

 Calculations:

(W2 – W1)

Specific gravity of the soil = G =    --------------------------------

(W2 – W1) – (W3 – W4)

 Where,         W1 = weight of the empty bottle with stopper.

W2 = weight of the bottle + Soil sample with stopper.

W3 = weight of the bottle + sample + water with stopper.

W4 = weight of the bottle + water with stopper.

  

4. MOISTURE CONTENT TEST.

( IS : 2720 – PART – 2 )

Object:

To determine the water content of a soil sample by oven drying method / sand bath method / Rapid moisture meter method.

 Apparatus:

 1) Non-corrodible airtight containers.

 2) Heat resistant tray – 5 to 7 cm deep.

 3) Rapid moisture meter and absorbent (calcium carbide).

 4) Oven, balance and heater / stove etc.

Procedure:

(A) Oven drying method: Take about 30 to 50 gms of soil sample if it is fine grained and about 250 to 300 gms if it is coarse grained soil in to the container and weigh it (W1).

Place the container in the oven and dry for 24 hours at temperature of 105 to 110 deg. C.

Remove the container from the oven replace the lid and cool it, after cooling weigh the container along with lid (W2). Clean and dry the container and weigh it (W3).

 

Calculations:

  

Water content, w % =  {(W1 – W2) / (W2 – W3)} X 100

    

(B) Sand bath method: Clean the container with lid or the tray, as the case may be dry and weigh (W1). Take the required quantity of the soil specimen in the container crumbled and placed loosely and weigh (W2). Add a few pieces of white paper if necessary. Place the container with the lid removed or the tray on the sand bath and heat the sand bath. Care shall be taken not to get the sand bath too hot. During heating, the specimen shall be turned frequently and thoroughly with the palette knife to assist the evaporation of water, care being taken to see that no soil is lost in the process. When drying is complete, remove the container from the sand bath, cool and weigh (W3).

Calculations:

   (W2 – W3)

Water content, w % = --------------- X 100

   (W3 – W1)

Note: Avoid over heating, A convenient method of detecting overheating of the soil is by the use of small pieces of white paper mixed the soil. Overheating is indicated if the paper turns brown.

(C) Rapid Moisture Meter: Set up the balance, place sample in pan till the mark on the balance arm mass lines up with the index mark (taken approximately 6 grams of soil).

Unclamp the clamping screw of the instrument sufficiently to move the U-clamp off the cup. Lift off the cup, check that cup and body are clean; otherwise clean it by using abrush. Hold the body horizontal and gently deposit one level scoopful of absorbent (calcium carbide) halfway inside the chamber. Then lay the chamber down without disturbing the absorbent charge. Transfer the soil weighed out as above from the pan to the cup. Holding cup and chamber approximately horizontal bring them together without disturbing sample or absorbent, bring the U-clamp round and clamp the cup tightly into place.

With gauge downwards (except when the steel balls are used) shake the moisture meter up and down vigorously for 5 seconds, then quickly turn it so that the gauge is upwards, give a tap to the body of the moisture meter to ensure that all the contents fall into the cup. Hold the rapid moisture meter downwards, again shake for 5 seconds then turn it with gauge upwards and tap. Hold for one minute and repeat this, when the needle comes to rest on the reading. The reading on the meter is the percentage of water content of the wet mass.

 

Calculations:

From the water content (m) obtained on the wet mass basis as the reading on the rapid moisture meter, the water content (w) on the dry mass basis shall be calculated as follows:

 w, % = {m/(100 – m)} X 100 , percent.

Where,           m = moisture content on the wet mass basis, obtained from rapid moisture meter.

w = moisture content on the dry mass basis

  

5. FREE SWELL INDEX TEST.

( IS : 2720 – PART – 40 )

Object:

To determine the free swell index of soils.

 Apparatus:

1) 425 micron IS sieve

 2) Glass graduated cylinders – 2 nos 100ml capacity

 3) Distilled water and kerosene.

 Procedure:

Take two 10 grams soil specimens of oven dry soil passing through 425-micron IS sieve.

Each soil specimen shall be poured in each of the two glass graduated cylinders of 100ml capacity. One cylinder shall then be filled with kerosene oil and the other with distilled water up to the 100ml mark. After removal of entrapped air the soils in both the cylinders shall be allowed to settle. Sufficient time (not less than 24 hours) shall be allowed for the soil sample to attain equilibrium state of volume without any further change in the volume of the soils. The final volume of soils in each of the cylinders shall be read out.

 Calculations:

The level of the soil in the kerosene-graduated cylinder shall be read as the original volume. The soil samples, kerosene being a non-polar liquid does not cause swelling of the soil. The level of the soil in the distilled water cylinder shall be read as the free swell level. The free swell index of the soil shall be calculated as follows:

Free swell index, percent = { (Vd – Vk) / Vk } X 100

    

 Where,                     Vd = the volume of soil specimen read from the graduated cylinder                                                   containing distilled water.

Vk = the volume of soil specimen read from the graduated cylinder                    containing kerosene.