SOILS TESTING



DRY PREPARATION OF SOIL SAMPLE FOR TESTING 

IS: 2720 - Part 1 

1. Introduction

This method describes the preparation of soil samples received from the field for mechanical analysis, physical tests, compaction tests etc.

2. Apparatus

(i) Wooden Mallet-for breaking clods.

(ii) Pulverizing apparatus.

(iii) A suitable riffle sampler or sample splitter for quartering samples

(iv) IS test sieves of sizes 75 mm, 63 mm, 37.5 mm, 19 mm, 13.2 mm, 9.5 mm, 6.7 mm, 4.75 mm, 2.00 mm and 425 micron.

(v) Trays for air drying soil with non-corroding metal. (vi) Drying oven, thermostatically controlled, capable of maintaining temperatures of 110± 5°C for drying soil samples.

(vii)  Balances of capacities 10 kg with sensitivity 100 gm, 1 kg with sensitivity of 1 gm and 250 gm with sensitivity 0.01 gm.

3. Preparation of the soil sample

(i) The sample received from the field is air dried or dried in the drying apparatus at temperature not exceeding 60°C.

(ii) The type, temperature and duration of drying are indicated in table 1 below. 

Table 1: Quantity of sample required for various tests

Sl. No Test  Type, temperature and duration of drying  amount of soil sample required for testing  Degree of pulverisation 
1 Water content Oven, 24 h As given in table 2 -
2 Specific gravity  Oven, 105110°C, 24 h  50 gm  for fine grained soils, 400 gm for fine medium and coarse grained soil  2 mm  (for fine grained soil)
3 Grain size analysis Air drying As given in table 3 -
4 Liquid limit Air drying 270 gm 425 micron
5 Plastic limit Air drying 60 gm 425 micron
6 Shrinkage factors Air drying 100 gm 425 micron
7 Light Compaction Air drying 6 kg (15 kg if soil is 19 mm
susceptible to crushing)
8 Heavy compaction Air drying do 19 mm
9 CBR Air drying 6 kg  
10 Permeability (200 110°C, 24 h mm dia) Oven, 105 -   2.5kg (100 mm dia)/5kg  9.5 mm
11 Chemical test - Organic matter Air drying 100 gm 2 mm
12 Sand Equivale nt value  Oven, 105±5°C 1500 gm 4.75 mm
13 Free swell index Oven dry 20 gm 425 micron

(iii) The material is separated into two parts using riffle sampler or by quartering.

(iv) Gravelly soils shall not be quartered by forming a cone. The entitrematerial shall be thoroughly mixed, spread flat, split into quadarnts and quartering done.

(v) Aggregations of soil particles are broken up using the pulverizing apparatus but without breaking their natural size.

(vi) Big clods shall be pulverised with wooden mallet. Further, pulvurising shall be carried out in pestle and mortar.

(vii) The pulverised soil is then passed through the specified sieve for testing. Any material retained is again subject to pulverisng with out breaking the particles.

(viii) The quantity of material required for water content determination shall be as given in table 2.

Table 2: Quantity of sample required for moisture content determination

Size of particles more than 90% passing IS sieve Minimum quantity of soil to be taken for the test (in gm)
425-micron 25
2-mm 50
4.75 mm 200
9.50 mm 300
19 mm 500
37.5 mm 1000

(ix) The quanity of soil required for grain size analysis shall be as given in table 3. 

Table 3: Quantity of soil required for grain size analysis

Maximum size of material (in mm)  Mass to be taken for test (in kg)
75 60
37.5 25
19 6.5
13.2 3.5
9.5 1.5
6.7 0.75
4.75 0.4

 4. Test sample for other tests  For the quantity of materials for other tests, refer to the specific test procedure.   

GRAIN SIZE ANALYSIS OF SOILS 

IS: 2720 - Part 4

1. Introduction

This test covers the method for the quantitative determination of grain size distribution of soils.  Two methods are given for finding the grain size distribution of soil particles larger than 75 micron:

a) In the wet analysis method, wet sieving of the soil is done.

b) The dry analysis is applicable to soils which do not have an appreciable amount of clay.

c) For finding the grain size analysis of soils smaller than 75 micron size, pipette method is considered as the standard method.

d) Hydrometer analysis also can be adopted as a subsidiary method. However, this method is not applicable if less than 10% of the material passes 75 micron sieve. e) Soil fraction retained on 4.75 mm and passing 4.75 mm IS sieves shall be separately taken for analysis.

2. Apparatus

(i) Any suitable apparatus capable of drying samples at temperature not exceeding 60°C.

(ii) IS test sieves 100 mm, 75 mm, 19 mm, 4.75 mm, 2.00 mm, 425 micron, 75 micron and other sizes as required for the specified tests.

(iii) Rubber pestle and mortar.

(iv) Sieve brushes and a wire brush or similar stiff brush.

(v) Weighing balance sensitive to 0.1% of the weight of sample.

(vi) Drying oven thermostatically controlled with non-corroding material interior, capable of maintaining temperature between 105°C and 110°C for drying wet samples.

(vii) Pulverizing apparatus like rubber covered pestle and mortar or any mechanical device capable of breaking aggregations without reducing the size of the individual grains.

(viii) A suitable riffle sampler or sample splitter.

(ix) Chemical reagent sodium hexametaphosphate or any other suitable dispersing agent.

(x) Miscellaneous equipments like trays or pans 300 mm dia and 75 mm depth for collecting the wash water from sieve, metal or rigid plastic trays or basins 45 cm2 to 90 cm2 area and 100 to 150 mm deep for soaking soil samples, containers for storing samples without loss of moisture etc.

3. Procedure for the sieve analysis of soil fraction retained on 4.75 mm IS sieve (Dry method)

a) The sample from the field is air dried or oven dried at 60°C.

b) The aggregations shall be then thoroughly broken in a mortar with rubber covered pestle.

c) A representative sample is then selected by the method of quartering or by using sampler.

d) The portion of air dried sample selected for the purpose of mechanical analysis and physical tests shall be weighed. 

e) The sample is then separated into two parts using 4.75 mm IS sieve.

f) The material retained on 4.75 mm IS sieve is weighed and mass recorded as uncorrected for hygroscopic moisture.

g) The material passing 4.75 mm sieve is carefully stored for analysis by method given under item 4.

h) The quantity of soil sample taken shall depend on the maximum particle size present in the soil in substantial quantities as given in table 1 below:

Table 1: Quantity of soil samples for analysis

Max size of particle (mm) present in substantial quantities Mass of sample taken for test in kg
75 60
40 25
25 13
19 6.5
12.5 3.5
10 1.5
6.5 0.75
4.75 0.4

i) The sample is separated into various fractions by sieving through the desired sieves.

j) While sieving through each sieve, the sieves shall be agitated such that the particles roll over the mesh of the sieve in an irregular motion.

k) Particles shall not be forced through the sieve openings. The materials in the sieve may be rubbed with rubber pestle taking care that individual particles are not broken.

l) The quantity taken in each sieve for sieving shall be such that the maximum weight retained in the sieve after sieving shall not exceed the values given in table 2. 

Table 2: Maximum weight of material allowed to be retained. 

IS sieve designation in mm 450 mm dia sieves in kg 300 mm dia sieves in kg
80 15 6
20 4 2
4.75 1 0.5

m) The mass of the material retained on each sieve is recorded. It the sample appears to contain more than 5% moisture, then amount of moisture shall be determined as per IS: 2720 (Part 2) and necessary corrections applied.

n) The percentage of soil retained on each sieve shall be calculated on the basis of the total mass of soil sample taken and from these results the percentage passing through each of the sieves shall be calculated.

4. Procedure for the sieve analysis of soil fraction passing 4.75 mm IS sieve and retained on 75 micron IS sieve

4.1 Analysis by wet sieving

a) The portion of the soil passing 4.75 mm IS sieve obtained as per item 3 above is oven dried at 105°C to110°C.

b) The oven dried material is riffled to get a convenient mass.  

c) This quantity shall be 200 gm, if major portion is particles close to 4.75 mm. If particle sizes are smaller a lesser sample size is sufficient.

d) This shall be weighed to 0.1% of its total mass and the mass recorded.

e) The sample is then spread in a large tray or basin and covered with water.

f) Take one litre of water. Add two grams of sodium hexametaphosphate. Alternately, one gram of sodium carbonate and one gram of sodium hydroxide can be used.

g) Add this prepared solution of dispersing agent to the soaked soil sample.

NOTE: The amount of dispersing agent may vary depending upon the type of soil. In some cases a dispersing agent may not be required.

a) Thoroughly stir the mix and keep for soaking.

b) The soaked soil is washed thoroughly over the set of IS sieves 2.0 mm, 425 micron and 75 micron. Continue washing till water passing through each sieve is substantially clean.

c) The fraction retained in each sieve is emptied carefully and oven dried at 105°C to110°C. Fraction in each sieve is weighed separately.

d) Alternately the washing of the soil sample can be done using 75 micron sieve till the water passing is substantially clean. The fraction retained on 75 micron sieve is then dried in oven and sieved through various sieves to get the fraction retained on each sieve.

e) The permissible maximum mass of material to be retained on 200 mm diameter sieve is as given in table 3

Table 3: Maximum weight of material allowed to be retained

IS sieve designation  Maximum mass of sample in gm 
2.0 mm  200 
425 micron 50
75 micron  25

4.2 Analysis by dry sieving

a) This method is not applicable to clayey soils.

b) The portion of the soil passing 4.75 mm IS sieve obtained as per item 3 above is oven dried at 105°C to110°C.

c) A representative portion of the soil shall be weighed to 0.1% of its total mass and the mass recorded.

d) The test sample is sieved through the required sieves.

e) Agitate the sieves while sieving so that sample rolls in an irregular motion over the sieves. No particles shall be pushed through the sieves.

f) Material remaining on the sieve shall be rubbed with a rubber pestle to ensure that only individual particles are retained on the sieve.

g) The material in the receiver is transferred to a steel tray.

h) The next sieve is fitted to the receiver. The material in the tray is again sieved.

i) Repeat the process till all the specified sieves are finished.

 j) If mechanical shaker is used, the sieving is carried out in one operation.

k) Care shall be taken to ensure that sieving is complete. 

l) A minimum of 10 minutes shaking shall be done.

m) The soil fraction retained on each sieve is carefully collected in containers and weight determined accurately.

5. Calculation

The cumulative mass of soil fraction retained on each sieve is calculated. The percentage retained on each sieve is then calculated from the weight of sample passing 4.75 mm sieve taken for sieving. The combined grading of the material is then worked out on the basis of the total sample tested and represented in a semi-log graph as shown below. 

DETERMINATION OF WATER CONTENT OF SOILS 

IS: 2386 - Part II Method I: Oven drying method 

1. Introduction

Water content or moisture content of a soil is the ratio of a given weight of water in a given soil sample to the weight of solid present in the soil sample. The given soil mass is dried in an oven at 105°C to110°C to constant weight to remove the water. The weight of soil remaining after oven drying is the solid particles in the soil sample.  Test samples shall be in accordance with the table 1, unless specified otherwise

Table 1: Recommended weight of sample for moisture content determination 

Max. particle size in the soil

IS sieve designation

Minimum sample weight in gm

425 micron

25

2.0 mm

50

4.75 mm

200

9.5 mm

300

19.0 mm

500

37.5 mm

1000

2. Apparatus

(i) Any suitable non-corrodible air tight container.

(ii) Weighing balance of sufficient sensitivity to weigh the soil samples to an accuracy of 0.04 percent of weight of the soil taken for the test.

(iii) Thermostatically controlled oven capable of maintaining temperatures of 105°C to 110°C for drying wet samples.

3. Procedure

a) Weigh accurately a clean dry container with lid (W1) and place the wet soil sample in it.

b) Replace the lid immediately and weigh the container and soil with the lid (W2).

c) Now remove the lid and place the container in the oven maintained at 105°C to 110°C and dry to constant  mass (W3) .

NOTE: It is not practical to check every soil sample to determine that it is dried to constant weight - normally 15 to 16 hrs. In case of doubt, drying should be continued till two successive readings are constant. New wet samples shall not be placed before removing dry samples from the oven.

4. Calculation

The water content w of the soil is given by:

w = [(Wt of water/wt of soil)] x 100 % and is reported to the nearest 0.1 percent. = [(W2 - W3)/(W3 – W1)] x 100 percent.

Report the result in the format attached with 2 significant digits accuracy.

Method II:  Sand-bath method

1. Introduction

This method is used for determination of the water content of a soil as a percentage of its dry mass. This test is less accurate and more suitable as a field test. The method shall not be used if it is suspected that the soil contains a large proportion of gypsum, calcareous matter or organic matter. 

2. Apparatus\

(i) Any suitable non corrodible air tight container.

(ii) Heat-resistant tray of suitable metal and about 5 to 7 cm deep.

(iii) Weighing balance of sufficient sensitivity to weigh the soil samples to an accuracy of 0.04% of weight.

(iv) Sand-bath containing clean sand to a depth of at least 3 cm.

(v) Kerosene stove or spirit lamp for heating the sand-bath

(vi) One palette knife or steel spatula about 20 cm long and 10 cm wide.

3. Procedure

a) Clean the container, dry and weigh (W1).

b) Take the required quantity of the soil specimen in the container, crumbled and placed loosely and weigh (W2).

c) Add a few pieces of white paper so that overheating will be indicated if the paper turns brown.

d) Place the container on the sand-bath and heat the sand-bath. Overheating should be strictly avoided.

e) During heating, the specimen shall be turned frequently and thoroughly with the palette knife.

f) When drying is complete, remove the container from the sand bath, cool and weigh with the lid (W3).

4. Calculation

The percentage of water content w is calculated as follows:

w = [(W2-W3)/ (W3-W1)] x100 where

w = Water content percent.

W2 = Mass of container with lid (or tray) with wet soil in gm.

W3 = Mass of container with lid (or tray) with dry soil in gm.

W1= Mass of container with lid (or tray) in gm.

Report the result in the format attached. 

Method III: Alcohol method 

1. Introduction

This method covers the determination of the water content of a soil as a percentage of its dry mass. This method is less accurate and is more suitable as a field test. Since methylated spirit is used, care shall be taken against risk of fire. The method shall not be used if the soil contains a large proportion of clay, gypsum, calcareous matter or organic matter.  Test samples shall be in accordance with the table 2, unless specified otherwise

Table 1: Recommended weight of sample for alcohol method.

Size of particles more than 90%  passing IS sieve designation Minimum quantity of soil specimen in gm to be taken for test
2 mm 30
19 mm 300

2. Apparatus

(i) Evaporating dish, 10 to 15 cm in diameter.

(ii) Weighing balance of sufficient sensitivity to weigh the soil samples to an accuracy of 0.04% of weight.

(iii) One palette knife or steel spatula having a blade 10 cm long and 2 cm wide.

(iv) Methylated spirit.

3. Procedure

a) Clean the evaporating dish, dry and weigh (W1).

b) Take the required quantity of the soil specimen in the evaporating dish and weigh (W2).

c) Pour methylated spirit over the soil so that the soil is well covered.

d) Mix the methylated spirit well into the soil with the palette knife and break up any large lumps of soil.

e) Place the evaporating dish on a surface which will not be affected by heat and ignite the methylated spirit.

f) Stir the soil constantly with the spatula.

g) After the methylated spirit has burnt away completely allow the dish to cool and weigh it with the contents (W3).

4. Calculation

The percentage of water content w, is calculated as follows:

w = [(W2-W3)/ (W3-W1)] x100 where,

w = Water content percent.

W2 = Mass of dish with wet soil in gm.

W3 = Mass of dish with dry soil in gm.

W1 = Mass of dish in gm.

Report the result in the format attached.

Method IV: Calcium Carbide method 

1. Introduction

This is a method for rapid determination of water content from the gas pressure developed by the reaction of calcium carbide with the free water of the soil. This test requires about 6 gm of soil sample.

2. Apparatus

(i) Metallic pressure vessel, with clamp for sealing cup, and a gauge calibrated in % water content.

(ii) A counterpoised balance  for weighing sample.

(iii) A suitable scoop for measuring absorbent (Calcium Carbide).

(iv) One bottle of the absorbent, Calcium Carbide.

(v) One Cleaning brush.

(vi) Three steel balls of about 12.5 mm diameter and one steel ball of 25 mm diameter

3.  Procedure

a) Set up the balance.

b) Place sample in pan till the mark on the balance arm mass lines with the index mark.

c) Unclamp the clamping screw of the instrument sufficiently to move the U-clamp off the cup. Lift off the cup.

d) Gently deposit the absorbent to fill half of the chamber. Then lay the chamber down without disturbing it.

e) Transfer the soil from the pan to the cup.

f) Holding approximately horizontal, bring the cup and chamber together without disturbing sample. Bring the U-clamp round and clamp the cup tightly into place.

g) With gauge downwards, shake the moisture meter up and down vigorously for 5 seconds. Then quickly turn it so that the gauge is upwards. Ensure that all the contents fall into the cup.

h) Hold the rapid moisture meter downwards. Again shake for 5 seconds, then turn it with the gauge upwards and tap. Hold for one minute. Repeat this for a third time.

i) Invert the rapid moisture meter one more time. Shake up and down to cool the gas.

 j) Turn the rapid moisture meter with the gauge upwards and dial horizontal, held at chest height.

k) When the needle comes to rest take the reading. The readings on the meter (m) are the percentages of water on the wet mass basis.

l) Finally release the pressure slowly by opening the clamp screw and taking the cup out.

m) Empty the contents and clean the instrument with a brush.

4. Calculation

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 is calculated as follows: w = [m/ (100-m)] x 100% 

DETERMINATION OF WATER CONTENT-DRY DENSITY RELATION OF SOILS USING LIGHT COMPACTION
IS: 2720 - Part 7 

1. Introduction

These methods are intended to determine the maximum dry density (MDD) and optimum moisture content (OMC) of soil under light (Standard) compaction.

a) In this method, a 2.6 kg rammer falling through a height of 310 mm is used.

b) The test is carried out on soils passing 19.0 mm IS sieve.

c) The soils can be compacted either in 1000 ml or 2250 ml mould.

d) The fraction of soil retained on 19.0 mm sieve is discarded (up to 5%).

e) If the soil contains larger proportion of gravel retaining on 19.0 mm sieve, the use of bigger mould (2250 ml) is recommended.

f) For soils not susceptible to crushing during compaction, about 6 kg of air dried material is required.

g) However if the soil to be tested contains granular material of soft nature like soft limestone, sandstones etc the sample required is about 15 kg.

2. Apparatus

(i) Cylindrical mould of capacity 1000 ml (or 2250 ml) with detachable base plate and removable collar of 6 cm height.

(ii) Rammer 2.6 kg having a flat circular face equipped with suitable guide sleeve for a free fall of 310 mm conforming to IS: 9198-1979.

NOTE: If mechanical rammer is used it shall be suitably calibrated.

(iii) Sample extruder consisting of a jack, lever, frame etc.

(iv) Balances, one with approximate capacity 15 kg, when used with 2250 ml mould with sensitivity of 1 gm and one with capacity 200 gm with sensitivity of 0.01 gm.

(v) Drying oven, thermostatically controlled, capable of maintaining temperatures of 110 ± 5°C for drying wet samples.

(vi) Straight edge of hardened steel about 300 mm length.

(vii) IS Sieves 19 mm and 4.75 mm conforming to the requirement of IS 460: Part I – 1985- Specification for wire cloth test sieves.

(viii) Mixing tools such as tray or pan, spoon, trowel, spatula etc for thoroughly mixing soil with water.

(ix) Containers made of corrosion resistant material with close fitting lids, one container each for one moisture content determination.

3. Procedure for soil not susceptible to crushing during compaction

a) Mix thoroughly 5 kg of the dried soil sample passing 19 mm, with water to dampen it to approximately 4% below OMC.

NOTE: For sandy and gravelly soils, 4% to 6% moisture will be sufficient. For cohesive soils 8% to 10% is required

b) Fill in the 1000 ml mould in three approximately equal layers. Compact each layer with 25 uniformly distributed blows with the free fall of 310 mm.

c) After compacting each of the first two layers, any loose soil adjacent to the mould walls shall be trimmed using a knife or spatula and evenly distributed on top of the compacted layer.

d) After filling each layer, give a slight tamp with the rammer, if the soil is loose or in a fluffy state.

e) After compaction, remove the extension collar, trim the compacted surface of the soil, even with the top of the mould, using the straight edge.

NOTE: It is necessary to control the quantity of soil compacted in the mould. If the amount of soil struck after removal of the collar is too great, it is likely to affect the accuracy of the result

f) Weigh the compacted soil in the mould with the base plate to the nearest 1 gm.

g) Remove the soil from the mould, slice vertically through the centre, take a sample of about 50 gm in a container and proceed with moisture content determination as per IS 2720 (Part II Determination of water content).

h) Thoroughly break up the remaining portion of the soil from the mould, rub through 19.0 mm sieve and add to the sample in the mixing tray or pan.

 i) Repeat the process with 1% to 2% increments of water.

NOTE: Water increments shall be normally 1% to 2% of sample weight except in the case of cohesive soils where increments up to 4% are allowed.

j) The mixing and compacting process is continued till a decrease in the weight of compacted soil is recorded.

NOTE: For soils containing coarse material up to 40 mm size, 2250 ml mould shall be used for compaction. A sample weighing about 6 kg passing IS sieve 19.0 mm is used. Soil is compacted in approximately three equal layers but given 55 blows of the 2.6 kg rammer. The rest of the procedure is same as given under 3 above.

4. Procedure for soil susceptible to crushing during compaction

a) The test procedure will be the same as given under 3 above, but the weight of total sample required will be 15 kg.

b) Five or six 2.5 kg air dried soil samples shall be taken and each mixed with different percentages of water.

c) After compaction of each sample, the remaining compacted material from the mould is discarded.

5. Calculations

Moisture content w of the compacted specimen is calculated using the equation:

w = [(A – B)/B –C)] x 100 % where

A = Weight of wet soil + container,

B = Weight of dry soil + container and

C = Weight of container.

Dry density (Or unit weight), ? of the compacted soil is given by:

dry = wet/(1+ w

6. Reporting of result

The test data may be tabulated in the format attached.  The oven dry density ?dry (Y-axis) and corresponding moisture content percentage w (X-axis) are plotted in a graph

DETERMINATION OF WATER CONTENT-DRY DENSITY RELATION OF SOILS USING HEAVY COMPACTION 

IS: 2720 - Part 8

1. Introduction

These methods are intended to determine the maximum dry density (MDD) and optimum moisture content (OMC) of soil under heavy (Modified) compaction.

a) In this method, a 4.9 kg rammer falling through a height of 450 mm is used.

b) The test is carried out on soils passing 19.0 mm IS sieve.

c) The soils can be compacted either in 1000 cm3 or 2250 cm3 mould.

d) The fraction of soil retained on 19.0 mm sieve is discarded (up to 5%).

e) If the soil contains larger proportion of gravel retaining on 19.0 mm sieve, the use of bigger mould (2250 ml) is recommended.

f) For soils not susceptible to crushing during compaction, about 6 kg of air dried material is sufficient. However if the soil to be tested contains granular material of soft nature like soft limestone, sandstone etc the sample required is about 15 kg.

2. Apparatus

(i) Cylindrical mould of capacity 1000 cm3 (or 2250 cm3) provided with detachable base plate and removable collar of 6 cm height all conforming to IS: 10074-1982 – Specification for compaction mould assembly for light and heavy compaction of soils.

(ii) Rammer 4.9 kg having a flat circular face equipped with suitable guide sleeve for a free fall of 310 mm conforming to IS: 9198-1979 – Specification for compaction rammer for soil testing.

NOTE: If mechanical rammer is used it shall be suitably calibrated.

(iii) Sample extruder consisting of a jack, lever, frame etc.

(iv) Balances, one with approximate capacity 15 kg, when used with 2250 cm3 mould with sensitivity of 1 gm and one with capacity 200 gm with sensitivity of 0.01 gm.

(v) Drying oven thermostatically controlled with non-corroding material interior, capable of maintaining temperature between 105 oC and 110oC for drying wet samples.

(vi) Straight edge of hardened steel about 300 mm length and having one edge bevelled.

(vii) IS sieves 37.5 mm, 19 mm and 4.75 mm conforming to the requirement of IS 460: Part I – 1985- Specification for wire cloth test sieves.

(viii) Mixing tools such as tray or pan, spoon, trowel, spatula etc for thoroughly mixing soil with water.

(ix) Containers made of corrosion resistant material with close fitting lids, one container each for one moisture content determination.

3. Procedure for soil not susceptible to crushing during compaction

a) Mix about 5 kg of the air-dried soil sample with water approximately 4% below OMC to dampen it. It is important that soil is thoroughly mixed with the water added.

b) Fill in the 1000 cm3 mould in 5 approximately equal layers

c) Compact each layer with 25 uniformly distributed blows using 4.9 kg hammer with the free fall of 450 mm.

d) After compacting each of the first four layers, any loose soil adjacent to the mould walls shall be trimmed using a knife or spatula and evenly distributed on top of the compacted layer.

e) After filling each layer give a slight tamp with the rammer, if the soil is loose or in a fluffy state.

 f) After compaction, remove the extension collar and trim the compacted surface of the soil, even with the top of the mould using the straight edge.

NOTE: It is necessary to control the quantity of soil compacted in the mould. If the amount of soil struck after removal of the collar is too great, it is likely to affect the accuracy of the result.

g) Weigh the compacted soil in the mould with the base plate to the nearest 1 gm.

h) Remove the soil from the mould, slice vertically through the centre, take a sample of about 50 gm in a container and proceed with moisture content determination as per IS: 2720 (Part II-Determination of water content).

i) Thoroughly break up the remaining portion of the soil from the mould, rub through 19.0 mm sieve and add to the sample in the mixing tray or pan.

j) Repeat the process with 1% to 2% increments of water.

NOTE: Water increments shall be normally 1% to 2% of sample weight except in the case of cohesive soils where increments up to 4% are allowed.

k) The mixing and compacting process is continued till a decrease in the weight of compacted soil is recorded.

NOTE: For soils containing coarse material up to 37.5 mm size, 2250 ml mould shall be used for compaction. A sample weighing about 30 kg passing IS sieve 37.5 mm is used. Soil is compacted in approximately five equal layers but given 55 blows of the 4.9 kg rammer. The rest of the procedure is same as given under 3 above.

4. Procedure for soil susceptible to crushing during compaction

a) The test procedure will be the same as given under 3 above, but the weight of total sample required will be 15 kg.

b) Five or more 2.5 kg of air dried soil samples shall be taken and each mixed thoroughly with different percentages of water.

c) After compaction of each sample, the remaining compacted material from the mould is discarded.

5. Calculations

Moisture content w of the compacted specimen is calculated using the equation:

w = [(A – B)/B –C)] x 100 % where

A = Weight of wet soil + container,

B = Weight of dry soil + container and

C = Weight of container. Dry density of compacted soil is given by:

dry = wet/(1+ w)

6. Reporting of results

The test data may be tabulated in the format attached with light compaction test.  The oven dry density ?dry (Y-axis) and corresponding moisture content percentage w (X-axis) are plotted in a graph.  

DETERMININATION OF LIQUID LIMIT OF SOILS 

IS: 2720 - Part 5 

1. Introduction

The physical properties of fine grained soils, especially clay, differ much with the percentage of water content in it. Clay may be almost in a liquid state, or it may show plastic behavior or may be very stiff depending on the amount of moisture in it. Plasticity is the most outstanding property of clayey soils which can be termed as the ability to undergo changes in shape without rupture. Albert Mauritz Atterberg, a Swedish Chemist & Agriculturist in 1911, proposed a series of tests mostly empirical for the determination of the consistency and the plastic properties of fine grained soils. The limits he defined are Liquid Limit (LL), Plastic Limit (PL), Plasticity Index (PI) and Shrinkage Limit (SL). Atterberg suggested 2.0 micron as the limit for clay particles.  Liquid Limit is the minimum water content at which the soil will flow by the application of a small shearing force. Liquid limit of a soil is determined in the laboratory on samples passing 425 micron sieve. It is determined using Casagrande?s Liquid Limit Device.

2. Apparatus

(i) Liquid Limit Device with grooving tool and adjustment plate.

(ii) Porcelain evaporating dish for mixing.

(iii) Flat glass plate 10 mm thick, 45 cm square as an alternative to evaporating dish.

(iv) Spatula with blade 2 cm wide and 8 cm long.

(v) Palette knives two with blade about 20 cm long and 3 cm wide for mixing soil and water in the glass plate.

(vi) Wash bottle or beaker containing distilled water.

(vii) Height gauge.

(viii) Containers for moisture content determination.

(ix) Balance, sensitive to 0.01 gm.

(x) Thermostatically controlled oven, capable of maintaining temperatures between 105°C and 110°C.

3. Adjustment of the liquid limit device a) Check whether the device is in good order.

b) Side play will occur if the pin connecting the cup is worn. The screws connecting the hanger arm should be tight.

c) The point of contact of the cup and the base shall not be excessively worn.

d) The grooving tool shall be clean and dry.

e) The height through which the cup is lifted and dropped with the base falls through exactly one centimetre for one revolution of the handle. 

f) The adjustment plate is then secured by tightening the screw.

4. Procedure

a) About 120 gm of soil sample passing 425 micron sieve is thoroughly mixed with distilled water in the evaporating dish or glass plate to form a uniform paste.

b) The paste shall have a consistency that will require 30 to 35 drops of the cup to cause the required closure of the standard groove.

c) In the case of clayey soils, the soil paste shall be left to stand for a sufficient time (24 hours) so as to ensure uniform distribution of moisture throughout the soil mass. The paste should be remixed before the test.

d) A portion of the paste is placed in the cup above the spot where it touches the base. Squeeze and spread the soil paste in the cup with a spatula.

e) Trim off excess soil, if necessary, so that the maximum depth of soil in the cup is 10 mm.

f) Divide the soil paste through the middle by a firm stroke of the grooving tool so that a clean sharp groove is formed.

g) To avoid slipping of the soil cake, the grooving can be done in maximum six stages so that the last stroke touches the bottom of the cup.

h) The cup is lifted and dropped by turning the crank at the rate of 2 revolutions per second till the grove closes for a length of 12 mm.

NOTE: If the soil slides on the surface of the cup instead of flowing, the result should be discarded and the test is to be repeated until flowing occurs. If sliding still occur, a note can be made that liquid limit cannot be determined.

i) A slice of soil extending from edge to edge perpendicular to the grove is removed using the spatula and placed in the container for moisture content determination.

j) The soil remaining in the cup is transferred to the mixing dish and test continued for increased moisture content.

k) The cup and grooving tool is washed and dried for next trial.

NOTE: The trial should be done at least four times. The specimens shall be of such consistency that the number of drops required to close the groove shall be not less than 15 or more than 35.

5. Calculation 

a) The water content of the soil is expressed as a percentage of the weight of the open dried soil. Calculate the moisture content to the nearest percentage.

b) A „flow curve? showing the relationship between moisture content and number of shocks is plotted in a semi-logarithmic graph with moisture content in the arithmetic scale in the X-axis and number of drops as ordinates in the logarithmic scale.

c) The flow curve is a straight line drawn as nearly as possible through the four or more plotted points.  

d) From the graph, the moisture content corresponding to 25 drops is reported as the Liquid Limit of the soil. 

DETERMINING THE PLASTIC LIMIT AND PLASTICITY INDEX OF SOILS 

IS: 2720 - Part 5 

1. Introduction

Plastic limit of a soil is the lowest water content at which the soil remains plastic. Plastic limit is the moisture content at which a soil when rolled into a thread of smaller diameter starts crumbling when the diameter reaches 3.0 mm.

2. Apparatus

(i) Plastic Limit rolling device (optional).

(ii) Paper for rolling device,  

(iii) Ground-glass plate of about 20 cm x 15 cm size.

(iv) Porcelain dish for mixing.

(v) Spatula with blade 2 cm wide and 8 cm long.

(vi) Glass or metallic rod 10 cm long, 3 mm dia.

(vii) Air-tight containers for moisture content determination.

(viii) Balance, sensitive to 0.01 gm.

(ix) Thermostatically controlled oven capable of maintaining temperatures between 105°C and 110°C.

3. Procedure

a) Mix about 20 gm of over dry soil passing 425 micron sieve with distilled water in an evaporating dish until the soil mass becomes plastic enough to be easily shaped into a ball.

b) If soil is clayey, the plastic soil mass shall be left to stand for sufficient time (24 hours) to ensure uniform distribution of the moisture in the soil mass.

c) Take a ball of about 8 gm of this as test sample.

d) Roll this mass between the palm or fingers and the glass plate with just sufficient pressure to roll it into a thread of uniform diameter.

e) The rolling is continued till the diameter of the thread is 3.0 mm.

f) The soil thread is kneaded together into a ball and rolled again to form a thread of 3.0 mm.

g) The process of alternate rolling and kneading is repeated till the thread crumbles under pressure.

h) The thread of 3.0 mm dia which crumbles during rolling is transferred to a container for moisture determination.

i) The above process is continued till three consistent values of Plastic Limit are obtained.  

4. Calculation

a) The Plastic Limit is the mean value of the moisture content determination rounded to the nearest whole number.  

b) The Plasticity Index is calculated as the difference between the Liquid Limit and Plastic Limit.  Plasticity Index (Ip) = Liquid limit (wL) – Plastic limit (wp)

c) If liquid limit or plastic limit cannot be determined, it is reported as NP (non-plastic). 

DETERMINATION OF FREE SWELL INDEX OF SOILS 

IS: 2720 - Part 40 

1. Introduction

Free swell index is the increase in volume of the soil without any external constraints when subjected to submergence in water.

2. Apparatus

(i) Two graduated cylinders, 100 ml capacity each.

(ii) Balance with approximate capacity of 200 gm with sensitivity of 0.01 gm.

(iii) Drying oven thermostatically controlled with non-corroding material interior, capable of maintaining temperature between 105°C and 110°C for drying wet samples.

(iv) IS sieve 425 micron conforming to the requirement ofIS 460: Part I–1985 Specification for wire cloth test sieves.

3. Procedure

a) Take two specimens of 10 gm soil passing 425 micron IS sieve and oven dried.

b) Pour each soil specimen into 100 ml capacity graduate glass cylinders.

c) Pour distilled water in one and kerosene oil in other cylinder up to 100 ml mark.

d) Remove entrapped air by gentle shaking or stirring with glass rod.

e) Allow the sample in both cylinders to settle

 f) Allow attainment of equilibrium state of volume of suspension (for not less than 24 hours).

g) Final volume of soil in each of the cylinder shall be read out.

4. Calculations

The free swell index of the soil, in percentage, is calculated as follows:

Free swell index = (Vd - Vk)/ Vk x 100 where 

Vd = Volume of soil specimen read from the graduate cylinder containing distilled water.

Vk = Volume of soil specimen read from the graduate cylinder containing kerosene.

5. Reporting of result

The free swell index of the soil is reported in percentage. A correlation of Free swell index, degree of expansiveness and Plastic Limit of soil is given in the table below: 

Free swell index %

Degree of expansiveness

Plasticity Index

<20

Low

0-35

20-35

Moderate

25-50

30-50

High

35-65

>50

Very high

>45

DETERMINATION OF SAND EQUIVALENT VALUE OF SOILS 

IS: 2720 - Part 37 

1. Introduction

This method describes the procedure for determining the sand equivalent value of soils. The purpose of this test method is to indicate, under standard conditions, the relative proportions of clay-like or plastic fines and dusts in granular materials and fine aggregates, that pass the 4.75 mm IS sieve. A minimum sand equivalent value may be specified to limit the permissible quantity of clay-like fines in an aggregate. The test may also be used for determining changes in the quality of aggregates during production or placement.

2. Apparatus

(i) Graduated cylinder, of transparent acrylic plastic and a rubber stopper to fit the mouth of the cylinder.

(ii) Irrigator tube made of stainless steel tubing 6.4 mm outside dia, with one end closed to form a wedge shaped point. Two holes of 1 mm dia are drilled laterally through the flat side of the wedge near the point.

(iii) Siphon assembly including a 4 litre bottle, a 5 mm outside dia copper bent tube with a pinch clamp, a blow tube consisting of a 5 mm dia copper tube 50 mm long and a 50 mm blow hose, 3 mm dia and a rubber stopper to fit the graduated cylinder.

(iv) Weighted Foot Assembly of mass 1000±5 gm.

(v) Measuring cans of a capacity of 90±5 ml.

(vi)  IS sieve 4.75 mm.

(vii) Miscellaneous supplies such as suitable pan for mixing, funnel, timing device and a sand equivalent shaker.

3. Material

(i) Stock Calcium Chloride Solution: Prepare the stock solution by dissolving 480.4 gm of anhydrous calcium chloride in 2 liters of distilled water. Cool, filter and add 2179 gm of glycerin. Add 49.7 gm of formaldehyde and mix thoroughly and dilute to 4 litres.

(ii) Working Calcium Chloride Solution: Prepare working solution by diluting 90 ml of stock solution to 4 litres of distilled water.

NOTE: Local tap water may be used if established by sand equivalent tests that the results are not affected.

4.Sample Preparation

a) Screen the sample on the 4.75 mm sieve.

b) Materials retained on the sieve is rubbed between the hands and rescreened.

c) Combine the rescreened material with the original material and mix thoroughly.

d) Carefully obtain 1500 gm of test sample by quartering the combined material passing the 4.75 mm sieve.

e) Fill 4 measuring cans with the material passing 4.75 mm sieve. 

f) The test sample will consist of sufficient material to fill the measuring cans to a slightly rounded level above the brim after tapping.

g) Record the volume or mass of the material in each of the 4 measures.

h) Return the material, mix and prepare necessary sample for the test.

i) Dry each test specimen to constant mass at 105±5°C and cool to room temperature before testing.

5. Preparation of the apparatus

a) Fit the siphon assembly to a 4 litre bottle of working calcium chloride solution.

b) Place the bottle on a shelf, 915±25 mm above the working surface.

c) Start the siphon by blowing into the top of the solution bottle through a short piece of tubing while the pinch clamp is open.

d) When using either the mechanical or the manually operated sand equivalent shaker, fasten the apparatus to a firm and level mount.

6. Procedure

a) Start siphon and add working calcium chloride solution to a depth of 100±2 mm in the graduated cylinder.

b) Pour one of the samples into the cylinder using the funnel and tap firmly on the palm of hand to dislodge any air bubbles and aid in wetting the sample.

c) Leave the wetted sample undisturbed for 10±1 minutes.

d) 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.

e) Place the stoppered cylinder in the mechanical sand equivalent shaker, set the time, and allow the machine to shake the cylinder and the contents for 45±1 seconds.

f) Set the cylinder upright and remove the stopper.

7. Irrigation procedure

a) Keep the cylinder vertical with the base in contact with work place.

b) Insert the irrigator tube and start the flow, rinsing the material from the cylinder walls as the tube is lowered.

c) Force the irrigator through the material at the bottom of the cylinder

d) Flush the fine material into suspension by gentle stabbing and twisting of the irrigation tube to the bottom of the cylinder. This flushes the fine material into suspension above the coarser sand particle.

e) The process should be continued until the cylinder is filled to the 380 mm graduation

f) Raise the irrigator tube slowly and adjust the flow to the 380 mm level of the cylinder.

g) Allow the cylinder and contents to stand undisturbed for 20  minutes ±15 seconds for sedimentation. Start the timing immediately after withdrawing the irrigator tube. 

h) Record the "clay reading" from the cylinder gradations and if the reading lies between gradations, record the higher gradation.

i) Lower the weighted foot in the cylinder until it comes to rest on the sand.

j) As the weighted foot comes to rest on the sand, tip the assembly towards the graduations on the cylinder until the indicator touches the inside of the cylinder.

k)  Subtract 250 mm from the level indicated by the extreme top edge of the indicator and record this value as the „sand reading?.

l)  If clay or sand readings fall between 2 mm graduations, record the level of the higher graduation as the reading.

8.  Calculation

Calculate the sand equivalent using the following formula, record to the nearest whole number.

Sand Equivalent (SE) = (Sand Reading/Clay Reading) x 100

9. Reporting of results

When the result of this calculation is not a whole number, the sand equivalent (SE) shall be the next higher whole number.

Example: SE = 84/204 x 100 = 41.2 = 42 If it is desired to average a series of sand equivalent values, average the whole number values determined as described above. 

DETERMINATION OF ORGANIC CONTENT OF SOILS 

IS: 2720 - Part XXII 

1. Introduction

Organic matter is an undesirable constituent of the soil from the engineering point of view since it causes swelling or shrinkage of the soil from when the moisture content or the applied load changes. The estimation of organic matter, therefore, forms an important part of soil examination. A wide variety of both dry and wet combustion methods are in use for the determination of the organic matter of soils. Two methods which are widely in use are given in this revision of the BIS. These methods give reproducible results and the results are sufficiently accurate for common engineering purposes. The first method is given as the standard method and the other as an alternative method. 

Method I- Based on organic carbon content of soil 

2. Apparatus

(i) A chemical balance, sensitive to 0.001 gm.

(ii) Two volumetric flasks with1 litre capacity.

(iii) Two burettes of 25 ml each, graduated in 0.1 ml.

(iv) A thermostatically controlled oven, capable to maintain a temperature of 105 to 110°C with interior of non-corroding material.

(v) Pipettes of 10 ml and 1 ml, fitted with a rubber teat.

(vi) Two conical flasks of 500 ml capacity.

(vii)  Graduated measuring cylinders of 200 ml and 25 ml.

(viii) Desiccator with any desiccating agent other than sulphuric acid.

(ix) Glass weighing bottle approximately 25 mm in diameter and of 50 mm height fitted with a ground glass stopper.

(x) IS test sieves of 10 mm, 425 micron and receivers.

(xi) Wash bottle.

3. Reagents

(i) Potassium Dichromate normal solution: Dissolve 49.035 gm of Potassium Dichromate in distilled water to make 1 litre of the solutio

(ii) Ferrous Sulphate solution (Approximately 0.5 N): Dissolve about 140 gm of Ferrous Sulphate in 0.5 N Sulphuric acid to make 1 litre solution. Add 14 ml of concentrated Sulphuric acid to distilled water to make 1 litre of 0.5 N Sulphuric acid solution

NOTE: This solution is unstable in air. Hence should be kept tightly stoppered. It should be standardised against the potassium dichromate solution at least once in a week.

(iii) Sulphuric acid concentrated of specific gravity 1.836.

(iv) Orthophosphoric acid, 85% of specific gravity 1.70 to 1.75.

(v) Indicator solution: Dissolve 0.25 gm of sodium diphenylamine-sulphonate in 100 ml of distilled water.

4. Standardization of Ferrous Sulphate solution

a) Run 10 ml of the normal potassium dichromate solution from a burette into a 500 ml conical flask.

b) Add 20 ml of concentrated sulphuric acid and the mixture is swirled carefully and allowed to cool for some minutes.  

c) Add 200 ml of distilled water to the mixture followed by 10 ml of phosphoric acid and 1 ml of indicator, and the mixture shaken thoroughly.

d) Ferrous sulphate solution is added from the second burette in 0.5 ml increments, the contents of the flask being swirled, until the colour of the solution changes from blue to green.

e) A further of 0.5 ml of potassium dichromate is then be added changing the colour back to blue.

f) Ferrous sulphate solution is then added drop by drop with continued swirling until the colour of the solution changes from blue to green after the addition of single drop.

g) The total volume of ferrous sulphate solution used (X) shall be noted to the nearest 0.05 ml (1 ml ferrous sulphate solution is equivalent to 10.5/X ml potassium dichromate). 

5.Soil sample preparation for test

a) The soil samples as received from the field is prepared in accordance with IS: 2720-Part 1.

b) The portion of the air dried sample selected for the purpose of this test is weighed, its moisture content determined using separate sample for the purpose and the equivalent oven-dried weight (W1) is recorded.

c) It shall then be sieved on a 10 mm IS sieve and all particles other than stones crushed to pass through the sieve.

d) The equivalent weight on oven dry basis of the material passing 10 mm sieve (W2) shall be calculated and recorded to the nearest 0.1% of its total weight.

e) A sample weighing approximately 100 gm shall be obtained from the material passing the 10 mm IS sieve by quartering. This sample shall then be pulverized so that it passes the 425 micron IS sieve.

NOTE: This method gives high results of organic content in soils containing sulphides. The sulphides can be destroyed at this stage by the addition of dilute (2N) Sulphuric acid. Acid to be added until no further evolution of hydrogen sulphide occurs.

NOTE: This method gives high results of organic content in soils containing chlorides. The chlorides may be removed at this stage by washing the soil with distilled water until no turbidity is obtained when a drop of the washing water is tested with silver nitrate solution. Alternatively the effect of chlorides on the determination can be partly eliminated by using concentrated sulphuric acid in which silver sulphate has been dissolved in place of the concentrated sulphuric acid. If the ratio of carbon to chloride does not exceed unity, 25 gm silver sulphate per litre of sulphuric acid will be sufficient to precipitate the chloride.

6. Procedure

a) The sample of soil is placed in a glass weighing bottle and weighed nearest to 0.001 gm. a) A small quantity, from 5 gm to 0.2 gm, depending on the organic content is transferred to a dry 500 ml conical flask.  

b) The weighing bottle is reweighed and the equivalent weight on oven dry basis of soil specimen removed (W3) is calculated by difference, allowing for the moisture content of the soil.

NOTE: The size of the specimen for chemical analysis will vary with the amount of the organic matter present in the soil. As much as 5 gm may be required for soil low in organic matter and as little as 0.2 gm with a very peaty soil. After a number of determinations have been made

7. Irrigation procedure

a) Keep the cylinder vertical with the base in contact with work place.

b) Insert the irrigator tube and start the flow, rinsing the material from the cylinder walls as the tube is lowered.

c) Force the irrigator through the material at the bottom of the cylinder.

d) Flush the fine material into suspension by gentle stabbing and twisting of the irrigation tube to the bottom of the cylinder. This flushes the fine material into suspension above the coarser sand particle.

e) The process should be continued until the cylinder is filled to the 380 mm graduation.

f) Raise the irrigator tube slowly and adjust the flow to the 380 mm level of the cylinder.

g) Allow the cylinder and contents to stand undisturbed for 20 minutes ±15 seconds for sedimentation. Start the timing immediately after withdrawing the irrigator tube.

h) Record the "clay reading" from the cylinder gradations and if the reading lies between gradations, record the higher gradation.

i) Lower the weighted foot in the cylinder until it comes to rest on the sand

j) As the weighted foot comes to rest on the sand, tip the assembly towards the graduations on the cylinder until the indicator touches the inside of the cylinder.

k)  Subtract 250 mm from the level indicated by the extreme top edge of the indicator and record this value as the „sand reading?

l)  If clay or sand readings fall between 2 mm graduations, record the level of the higher graduation as the reading

8.  Calculation

Calculate the sand equivalent using the following formula, record to the nearest whole number.

Sand Equivalent (SE) = (Sand Reading/Clay Reading) x 100  9. Reporting of results  When the result of this calculation is not a whole number, the sand equivalent (SE) shall be the next higher whole number.

Example: SE = 84/204 x 100 = 41.2 = 42 If it is desired to average a series of sand equivalent values, average the whole number values determined as described above. 

DETERMINATION OF ORGANIC CONTENT OF SOILS 

IS: 2720 - Part XXII

1. Introduction

Organic matter is an undesirable constituent of the soil from the engineering point of view since it causes swelling or shrinkage of the soil from when the moisture content or the applied load changes. The estimation of organic matter, therefore, forms an important part of soil examination. A wide variety of both dry and wet combustion methods are in use for the determination of the organic matter of soils. Two methods which are widely in use are given in this revision of the BIS. These methods give reproducible results and the results are sufficiently accurate for common engineering purposes. The first method is given as the standard method and the other as an alternative method. 

Method I- Based on organic carbon content of soil 

2. Apparatus

(i) A chemical balance, sensitive to 0.001 gm.

(ii) Two volumetric flasks with1 litre capacity.

(iii) Two burettes of 25 ml each, graduated in 0.1 ml.

(iv) A thermostatically controlled oven, capable to maintain a temperature of 105 to 110°C with interior of non-corroding material.

(v) Pipettes of 10 ml and 1 ml, fitted with a rubber teat.

(vi) Two conical flasks of 500 ml capacity.

(vii)  Graduated measuring cylinders of 200 ml and 25 ml.

(viii) Desiccator with any desiccating agent other than sulphuric acid.

(ix) Glass weighing bottle approximately 25 mm in diameter and of 50 mm height fitted with a ground glass stopper.

(x) IS test sieves of 10 mm, 425 micron and receivers.

(xi) Wash bottle.

3. Reagent

(i) Potassium Dichromate normal solution: Dissolve 49.035 gm of Potassium Dichromate in distilled water to make 1 litre of the solution.

(ii) Ferrous Sulphate solution (Approximately 0.5 N): Dissolve about 140 gm of Ferrous Sulphate in 0.5 N Sulphuric acid to make 1 litre solution. Add 14 ml of concentrated Sulphuric acid to distilled water to make 1 litre of 0.5 N Sulphuric acid solution.

NOTE: This solution is unstable in air. Hence should be kept tightly stoppered. It should be standardised against the potassium dichromate solution at least once in a week

(iii) Sulphuric acid concentrated of specific gravity 1.836.

(iv) Orthophosphoric acid, 85% of specific gravity 1.70 to 1.75.

(v) Indicator solution: Dissolve 0.25 gm of sodium diphenylamine-sulphonate in 100 ml of distilled water.

4. Standardization of Ferrous Sulphate solution

a) Run 10 ml of the normal potassium dichromate solution from a burette into a 500 ml conical flask.

b) Add 20 ml of concentrated sulphuric acid and the mixture is swirled carefully and allowed to cool for some minutes.  

c) Add 200 ml of distilled water to the mixture followed by 10 ml of phosphoric acid and 1 ml of indicator, and the mixture shaken thoroughly.

d) Ferrous sulphate solution is added from the second burette in 0.5 ml increments, the contents of the flask being swirled, until the colour of the solution changes from blue to green.

e) A further of 0.5 ml of potassium dichromate is then be added changing the colour back to blue.

 f) Ferrous sulphate solution is then added drop by drop with continued swirling until the colour of the solution changes from blue to green after the addition of single drop.

g) The total volume of ferrous sulphate solution used (X) shall be noted to the nearest 0.05 ml (1 ml ferrous sulphate solution is equivalent to 10.5/X ml potassium dichromate).

5. Soil sample preparation for test

a) The soil samples as received from the field is prepared in accordance with IS: 2720-Part 1.

b) The portion of the air dried sample selected for the purpose of this test is weighed, its moisture content determined using separate sample for the purpose and the equivalent oven-dried weight (W1) is recorded.

c) It shall then be sieved on a 10 mm IS sieve and all particles other than stones crushed to pass through the sieve.

d) The equivalent weight on oven dry basis of the material passing 10 mm sieve (W2) shall be calculated and recorded to the nearest 0.1% of its total weight.

e) A sample weighing approximately 100 gm shall be obtained from the material passing the 10 mm IS sieve by quartering. This sample shall then be pulverized so that it passes the 425 micron IS sieve.

NOTE: This method gives high results of organic content in soils containing sulphides. The sulphides can be destroyed at this stage by the addition of dilute (2N) Sulphuric acid. Acid to be added until no further evolution of hydrogen sulphide occurs.

NOTE: This method gives high results of organic content in soils containing chlorides. The chlorides may be removed at this stage by washing the soil with distilled water until no turbidity is obtained when a drop of the washing water is tested with silver nitrate solution. Alternatively the effect of chlorides on the determination can be partly eliminated by using concentrated sulphuric acid in which silver sulphate has been dissolved in place of the concentrated sulphuric acid. If the ratio of carbon to chloride does not exceed unity, 25 gm silver sulphate per litre of sulphuric acid will be sufficient to precipitate the chloride.

6. Procedure

a) The sample of soil is placed in a glass weighing bottle and weighed nearest to 0.001 gm.

a) A small quantity, from 5 gm to 0.2 gm, depending on the organic content is transferred to a dry 500 ml conical flask.  

b) The weighing bottle is reweighed and the equivalent weight on oven dry basis of soil specimen removed (W3) is calculated by difference, allowing for the moisture content of the soil.

NOTE: The size of the specimen for chemical analysis will vary with the amount of the organic matter present in the soil. As much as 5 gm may be required for soil low in organic matter and as little as 0.2 gm with a very peaty soil. After a number of determinations have been made

DETERMINATION OF SPECIFIC GRAVITY OF FINE MEDIUM  AND COARSE GRAINED SOILS 

IS: 2720 - Part 3: Section 2

1. Introduction

This test lays down the procedure for the determination of specific gravity of soil particle of fine, medium and coarse grained soils. Specific gravity is the ratio of the weight in air of a given volume of soil solids at a specified temperature to the weight in air of equal volume of distilled water at that temperature. Specific gravity is required to find out the degree of saturation and unit weight of moist soils. The unit weight is needed in pressure, settlement and stability related problems in soil engineering.

2. Apparatue

a) A glass jar of 1000 ml capacity fitted with rubber bung or stopper.

b) Ground glass plate or a plastic slip cover for closing the jar.

c) A mechanical shaking apparatus capable of rotating the glass jar at about 50 revolutions per minute.

d) Weighing balance readable to 0.2 gm sensitivity.

e) A glass thermometer of range 0 to 50°C, readable to 1°C accuracy.

3. Procedure

a) Dry the gas jar and ground plate/plastic slip cover and weigh to the nearest 0.2 gm.

b) Take about 200 gm of fine grained soil or 400 gm of medium or coarse grained soil and dry in oven at 105°C to 110°C.  Cool this in a desiccator.

NOTE:  If there is a chance of loss of water of hydration, the soil should be dried at not more than 80°C.

c) Transfer this sample from desiccator direct to the gas jar. Weigh the gas jar with ground glass plate/slip cover and the soil sample to the nearest 0.2 gm.  

d) Add 500 ml of water within ±2°C of the average room temperature during the test into the jar. Insert the rubber stopper into the gas jar.

e) Keep aside the jar along with the contents for at least 4 hours if the soil is medium or coarse grained.  

f) If the sample is fine grained, shake the jar with hand immediately after the addition of water until the particles are in suspension.

g) Then place the jar in the shaking apparatus and shake for 20 to 30 minutes.

 h) Remove the rubber stopper and carefully wash any soil particles adhering to the stopper into the jar.

i) Add water to the jar within 2 mm of the top. Allow the soil to settle for few minutes. Fill the jar to the brim with more water.

j) Place the glass plate over the jar ensuring that no air is entrapped under the plate.

k) Wipe the outside of the gas jar dry and find the weight to the nearest 0.2 gm.

l) Empty the gas jar, wash thoroughly and fill with water up to the brim.

m) Place the glass plate over the jar with water, ensuring that no air is entrapped under the plate.

n) Wipe the outside of the gas jar and plate dry and find the weight to the nearest 0.2 gm.

o) Repeat the procedure with a second sample to obtain two values. 

NOTE:  If there is a large difference in air temperature, sufficient water should be drawn for the required number of tests and allowed to stand in room temperature in which the tests are done until the temperature is within the given range.

4. Calculation

The specific gravity of the soil at room temperature is given by:

G   = W2 – W1/ [(W4 – W1) – (W3 – W2)] where

W1 = Weight of gas jar + glass plate in gm.

W2 = Weight of gas jar + glass plate + soil in gm.

W3 = Weight of gas jar + glass plate + soil + water in gm.

W4 = Weight of gas jar filled with water + glass plate in gm.

Specific gravity is reported to the nearest 0.01. Specific gravity is calculated at 27°C. If the test is done at a different temperature, the corrected specific gravity is given by G¹ = K G, where  K = Relative density of water at room temperature/ Relative density of water at 27°C.

Report the result in the format attached.   

DETERMINATION OF SPECIFIC GRAVITY OF FINE GRAINED SOILS 

IS: 2720 - Part 3: Section I 

1. Introduction

The methods of test for the determination of specific gravity of fine grained soil particles are given under this part. Specific gravity is required to find out the degree of saturation and unit weight of moist soils. The unit weight is needed in pressure, settlement and stability problems in soil engineering.

2. Apparatus

(i) Two density bottles (pycnometer) with stoppers 50 ml capacity.

(ii) Water bath maintained at constant temperature within ±0.2°C (If standard density bottles are used, the constant temperature is 27°C).

(iii) One Vacuum Desiccator, about 200 to 250 mm diameter size.

(iv) One Desiccator about 200 to 250 mm diameter size containing anhydrous silica gel.

(v) A thermostatically controlled drying oven, capable of maintaining temperatures of 105°C to 110°C for drying wet samples.

(vi) A weighing balance, readable to 0.001 gm sensitivity.

(vii) A vacuum pump as a source of vacuum.

(viii) One spatula, about 150 mm long and 3 mm wide or 3 mm dia glass rod to go through the neck of the pycnometer.

(ix) Wash bottle made of plastic, containing air free distilled water.

(x) Multiple slot type sample divider (riffle box) with 7 mm wide opening.

(xi) Rubber tube to fit the vacuum pump and desiccator.

3. Procedure

a) Dry the pycnometer with stopper in oven at 105°C to 110°C, cool it in a desiccator and weigh to the nearest 0.001 gm (W1).

NOTE:  If a density bottle is used, it should not be dried in oven to avoid distortion. It may be dried by rinsing with acetone or an alcohol-ether mixture and then blowing with warm air.

b) Take about 50 gm of sample and ground if necessary, to pass through a 2 mm IS test sieve.

c) Obtain 5 gm to 10 gm of sample by riffling and dry in oven at 105 oC to 110°C.  Cool this in a desiccator.

NOTE:  If there is a chance of loss of water of hydration, the soil should not be dried at not more than 105°C.

d) Transfer this sample from desiccator direct to the density bottle. Weigh the bottle and sample to the nearest 0.001 gm (W2). 

e) Add sufficient air-free distilled water into the bottle such that the soil sample is just covered.

f) Keep the bottle along with the contents but without stopper, in a vacuum desiccator and evacuate gradually at a pressure of 20 mmHg.

g) During this process ensure that the air trapped in the soil do not bubble violently to prevent drops of suspension escaping through the mouth of the bottle. Continue this for at least one hour or till no further loss of air is apparent.

 h) The vacuum is released and lid of desiccator removed.

i) The soil in the bottle is carefully stirred with a spatula or vibrated. Before removing the spatula from the bottle, clean the particles of soil adhering to blade of the spatula using a few drops of air-free distilled water.

NOTE: Alternately the entrapped air can be removed by heating the pycnometer placed on a water-bath or sand-bath. j) Remove the bottle and contents from the desiccator and fill with air-free distilled water till the bottle is full. Insert the stopper.

k) Then immerse the bottle up to the neck in the constant-temperature bath at least for 1 hour or till it has attained the constant temperature of the bath.  NOTE: If a constant-temperature room or cabinet is available then keeping the bottle in constant-temperature bath is not necessary.

l) If there is apparent deduction in the volume of liquid inside the bottle, remove the stopper, fill the bottle with air-free liquid and replace the stopper.

m) Return the bottle to the constant-temperature bath and keep till the required temperature is attained. If the bottle is still not completely full, repeat the process.

n) Take the stoppered bottle out, wipe it dry and find the weight to the nearest 0.001 gm (W3).

NOTE: With certain soils containing soluble salts, kerosene or white sprit is used as testing liquid. In such cases, the specific gravity of the liquid at room temperature is carried out separately.

o) The volume of the density bottle has to be determined. For this, the bottle is then cleaned out and completely filled with air-free liquid. Insert the stopper.

p) Immerse the bottle with water in a constant temperature bath for minimum one hour or till it attains the constant temperature of the bath. It there is apparent deduction in the volume of liquid inside the bottle, remove the stopper, fill the bottle with air-free liquid and replace the stopper.

q) Return the bottle to the constant-temperature bath and keep till the required temperature is attained. If the bottle is still not completely full, repeat the process.

r) Take the stoppered bottle out, wipe it dry and find the weight to the nearest 0.001 gm (W4). Two determinations of the specific gravity of the same soil are normally carried out.

NOTE: Many soils contain substantial amount of heavy or light particles.

This may lead to erratic values of specific gravity. Hence it is recommended that a number of specific gravity determinations may be done to obtain a good average value.

4. Calculation

When air-free water is used, the specific gravity of the soil at room temperature is given by: G   = W2 – W1/ [(W4 – W1) – (W3 – W2)] where 

W1 = Weight of density bottle in gm.

W2 = Weight of density bottle + soil in gm.

W3 = Weight of density bottle + soil + water in gm.

W4 = Weight of density bottle filled with water in gm.

The average of the two values obtained is taken as the specific gravity. If the two results differ by more than 0.03, the test is repeated. Specific gravity is reported to the nearest 0.01. Report the result in the format attached.  If kerosene is used, the specific gravity G obtained as above is multiplied by the specific gravity of kerosene determined separately at the constant temperature.  Specific gravity is calculated at 27°C. If the test is done at a different temperature, the corrected specific gravity is given by G¹ = K G, where

K = Relative density of water at room temperature/Relative density of water at 27°C.   

DENSITY OF SOIL IN-PLACE FOR FINE AND MEDIUM GRAINED SOILS  BY SAND REPLACEMENT METHOD USING SMALL POURING CYLINDE

IS: 2720 - Part 28 

1. Introduction

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

a) The sand replacement method sometimes also termed as field density test is done for determining the in-place dry density of the compacted fine and medium grained soil.

b) This method covers the determination of in-place density of natural or compacted fine or medium grained soils for which a small sand pouring cylinder is used.

c) The method is not applicable for layers exceeding 150 mm thickness.

2. Apparatus

(i) Small sand pouring cylinder consisting of a metal cylinder of capacity 3 litres,115 mm 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.

(ii) Hand tools for excavating such as scraper with handle for leveling the surface, bent spoon, a dibber or an elongated trowel for digging and excavating the material.

(iii) Cylindrical calibrating container with an internal diameter of 100 mm and depth 150 mm. The volume of the container should be given to an accuracy of 0.25%.

(iv) Balance with approximate capacity 10 kg with the sensitivity of 1.0 gm,

(v) Glass or Perspex plate about 450 mm square and 9 mm thick or larger for calibration purpose.

(vi) Metal container of any convenient size about 150 mm diameter and 200 mm depth with a removable lid for collecting the excavated material.

(vii)  Metal tray 300 mm square and 40 mm deep with a 100 mm dia hole in the centre

(viii) Dry and clean test sand of uniform gradation passing 1.0 mm and retained on 600 micron IS sieve.

3. Calibration of the apparatus

a) Clean and oven dry the test sand, passing 1.0 mm IS sieve and retained on 600 micron IS sieve. Store for a period of one week for the water content in the sand to reach equilibrium with the atmospheric humidity.

b) Sand is collected in sufficient quantity required for at least three to four sets of test.

c) The top cap of the small sand pouring cylinder is removed and the shutter (above the cone) is closed.

d) The cylinder is filled with sand up to about 10 mm from the top and the cap is replaced.

e) The weight of the cylinder with the sand is determined accurate to 1 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.

f) The shutter is opened and sand equal to the volume of the calibration cylinder or the excavated test hole is allowed to flow out under gravity and the shutter is closed.

g) 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.

h) The shutter is closed, the cylinder is removed and the sand which occupied the cone is carefully collected from the plate and weighed (W2).

i) The sand pouring cylinder is refilled with sand such that the total weight is again W1.

j) Now the cylinder is placed centrally on the top of the calibration container and the shutter is opened. 

k) 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).

l) The above steps are repeated 3 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 of the level top can be determined.

m) The volume of the calibrating container V is determined either by measuring the internal dimensions or by filling with water and weighing.

n) From the weight of sand Wa and its volume V in the calibrating container, the density of sand is determined.

4. Measurement of field density

a) The point on the compacted layer where the field density test is to be conducted is cleaned and levelled using a scraper for an area of about 450 mm square.

b) The metal tray with 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 depth of 150 mm.

c) The loose material is removed and carefully collected in the metal container and is weighed (Ww).

d) The sand pouring cylinder is refilled with sand such that its weight is again W1.

e) The metal tray with central hole is removed and the sand pouring cylinder is placed centrally over the excavated hole.

f) 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.

g) The shutter is closed and the cylinder is weighed again (W4) so that the weight of the sand filling the excavated hole alone Wb can be found.

h) 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 110°C and reweighing (Method specified in IS:2720-Part 2).

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

j) 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.

5. Calculations

(a) Bulk density determination of sand:

Weight of cylinder + sand filled up to 10 mm from top edge = W1 gm.

Weight sand in the cone (mean value)  =

W2 gm. Weight of sand + cylinder after pouring into the calibration container and cone = W3 gm.

weight of sand + cylinder after pouring into the excavated hole and cone = W4 gm.

volume of calibrating container  = V ml. Weight soil from the excavated hole = Ww gm.

Weight of sand required to fill the hole = Wb gm. Weight of dry soil from the hole   = Wd gm.

Moisture content of the soil in % = w

The weight of sand filling the calibrating container only Wa = (W1-W3-W2) gm.

Bulk Density of sand, ?s   = (Wa/V) g/cm3.

(b) Bulk density determination of soil:

Weight of sand filling the excavated hole alone,

Wb  = (W1-W4-W2) gm. Weight of wet soil per cubic meter, ?b  = (Ww/Wb) x ?s kg/m3.

Dry density of soil, ?d = (Wd/Wb) x ?s kg/m3.

6. Reporting of results

The following values shall be reported:

a) Dry density of soil in kg/m3 to the nearest whole number or in g/cm3 correct to the second place of decimal

b) Water content of the soil in percent reported to two significant figures.

c) Compaction achieved in the field as a percentage of the maximum laboratory dry density. A typical format to record the results is attached

DETERMINATION OF LABORATORY CALIFORNIA BEARING RATIO

IS: 2720 - Part 16

1. Introduction

This test covers the laboratory determination of California Bearing Ratio (CBR). The ratio expressed as a percentage of the force per unit area required to penetrate a soil mass with a circular plunger of 50 mm diameter at the rate of 1.25 mm /min to that force required to penetrate a standard material is called CBR.  The ratio is usually determined for 2.5 mm and 5.0 mm penetrations of the plunger. Where the ratio is consistently higher for 5.0 mm penetration than for 2.5 mm, the ratio for 5.0 mm is used. The Standard load is obtained from test on crushed stone sample and is defined as CBR 100%. The test may be performed on undisturbed or remolded specimens. The remoulded specimens may be subjected to either static or dynamic compaction.

2. Apparatus

(i) CBR moulds provided with detachable base plate, removable collar, stay rods and wing nuts, spacer discs, surcharge weights etc all conforming to IS: 96691980 – Specification for CBR moulds and accessories.

(ii) Metal rammer conforming to IS: 9198-1979 – Specification for compaction rammer for soil testing.

NOTE: If mechanical rammer is used it shall be suitably calibrated.

(iii) Sample extruder consisting of a jack, lever, frame etc.

(iv) Penetration plunger conforming to IS: 9669-1980.

(v) Loading machine with at least 5000 kg capacity with a movable head or base which will enable the plunger to penetrate into the specimen at the rate of 1.25 mm/min.

(vi) Expansion measuring apparatus having adjustable stem with perforated plates and tripod conforming to IS: 9669-1980.

(vii) Two dial gauges reading to 0.01 mm accuracy.

(viii) Balances, one with approximate capacity 15 kg, when used with 2250 cm3 mould with sensitivity of 1 gm and one with capacity 200 gm with sensitivity of 0.01 gm.

(ix) Drying oven thermostatically controlled with non-corroding material interior, capable of maintaining temperature between 105°C and 110°C for drying wet samples.

(x) Straight edge of hardened steel about 300 mm length and having one edge bevelled.

(xi) IS sieves 37.5 mm, 19 mm and 4.75 mm conforming to the requirement of IS: 460 Part I – 1985 - Specification for wire cloth test sieves.

(xii)  Mixing tools such as tray or pan, spoon, trowel, spatula, calibrated measuring jar, filter paper etc. 

(xiii) Containers made of corrosion resistant material with close fitting lids, one container each for one moisture content determination.

3. Procedure for preparing undisturbed specimens

a) A steel cutting edge, 150 mm diameter, is attached to the mould and then pushed gently to the ground.

b) This process may be facilitated by digging away soil from outside as the mould is pushed down.

c) When the mould is full of soil, it shall be removed by under digging.

d) The top and bottom surfaces shall be trimmed flat so as to give the required length of specimen for testing.

e) The density of the soil shall be determined either by weighing the sample with the mould or by measuring the in-situ density by Sand Replacement method IS: 2720 (Part 28).

4. Procedure

for preparing disturbed specimens The material passing 19 mm IS sieve shall be used in the remoulded specimen. Allowance for fraction larger than 19 mm shall be made by replacing with equal amount of material passing 19.0 mm but retaining on 4.75 mm IS sieve.

4.1 Procedure for static compaction

A batch of soil shall be thoroughly mixed with water to give the required water content. The correct mass of the moist soils shall be placed in the mould and compaction obtained by pressing the displacer disc. A filter paper is placed between the disc and the soil.

4.2 Procedure for dynamic compaction

a) Mix about 4.5.kg of the air-dried fine grained soil or 5.5 kg of granular soil sample with the require amount of water to dampen it.

b) The soil is thoroughly mixed with the water added.

c) If the soil is to be compacted to the maximum dry density (MDD) at the optimum moisture content (OMC), the exact mass of soil required shall be taken and necessary water added so that the soil sample is at the optimum water content.

d) The mould with the extension collar attached is clamped to the base plate.

e) The spacer disc is then inserted over the base plate and a disc of coarse filter paper placed on the spacer disc.

f) Fill in the 2250 cm3 mould in five approximately equal layers for heavy compaction (IS: 2720 Part 8) and compact each layer with 55 uniformly distributed blows.  

g) For light compaction (IS: 2720 Part 7) fill the mould in five approximately equal layers and compact each layer with 25 uniformly distributed blows.

NOTE:  Some specifications may desire three specimens compacted with 10, 25 and 65 blows per layer.

h) While compacting the intermediate layers, any loose soil adjacent to the mould walls shall be trimmed using a knife or spatula and evenly distributed on top of the compacted layer.

i) After filling each layer give a slight tamp with the rammer, if the soil is loose or in a fluffy state.

j) After compaction, remove the extension collar, trim the compacted soil surface of the soil even with the top of the mould using the straight edge. Any hole that may develop on the surface during trimming shall be patched with smaller size material. 

NOTE: It is necessary to control the quantity of soil compacted in the mould. If the amount of soil struck after removal of the collar is too great, it is likely to affect the accuracy of the result.

k) Remove the perforated base plate and spacer disc and weigh the compacted soil in the mould to the nearest 1 gm.

l) A disc of coarse filter paper is then placed on the perforated base plate. The mould and the compacted soil is inverted and the perforated base plate is clamped to the mould with the filter paper below the compacted soil specimen.

NOTE: In both cases of compaction, if the specimen is to be soaked, representative samples of the material at the beginning of compaction and another sample of the remaining material after compaction shall be taken for moisture content determination. If the specimen is not soaked one cut piece of the material after penetration test is taken to determine the water content. The water content shall be determined in accordance with IS: 2720 (Part 2) – Determination of water content.

5. Procedure for measuring the swell

a) Place a filter paper over the compacted specimen. Place the adjustable stem and perforated plate over it.  

b) Weights to produce a surcharge equal to the weight of the base material and pavement to the nearest 2.5 kg shall be placed on the compacted specimen.

c) The whole mould and weights is then immersed in a tank of water. Allow free access of water to the top and bottom of the specimen.

d) The tripod for the expansion measuring device is mounted on the edge of the mould. The initial dial gauge reading is recorded. This set up shall be kept undisturbed for 96 hours noting down the readings after every 24 hrs.

e) At the end of the soaking period, the final dial gauge reading is noted. The tripod is then removed and the mould is taken out of water.

f) The free water collected on the top of the mould is removed and the specimen allowed drain out for 15 minutes. The surface of the specimen shall not be disturbed while water is drained water.

g) The weights, perforated plate and the top filter plate are removed.

h) The soaked specimen with the mould is weighed and the mass recorded. NOTE: The swell test may be omitted if it is not required in the specification

6. Procedure for measuring the penetration

a) The mould containing the specimen with the base plate in position, but the top face exposed, is placed on the lower plate of the testing machine.

b) The required number of surcharge weights is placed on the specimen. Initially one 2.5 kg surcharge is placed before the seating of the penetration plunger is done. The seating is done with a load of 4 kg to establish full contact between the plunger and soil surface.

c) Now the load and deformations gauges are set to zero. The load shall be applied at the penetration rate of 1.25 mm/min.

d) Readings of the load gauge are taken at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 4.0, 5.0, 7.5, 10 and 12.5. Raise the plunger and detach the mould from the loading equipment.

e) About 50 gm of soil is collected from the top 30 mm portion and water content determined as per IS: 2720 (Part 2).

f) If the average water content is to be determined, sample shall be taken from the entire depth of the specimen.

g) If undisturbed specimen is to be used in the test, examine carefully for any oversized particle directly below the plunger which are likely to affect the results.

NOTE: The penetration test may be repeated as a check test for the rear end of the sample.

7. Calculations

a) Expansion ratio: The expansion ratio of the soil tested is calculated as below from the swell measurements obtained as per item 5 above. Expansion ratio = [(df – ds)/h)] x 100 % where  df = Final reading of the dial gauge in mm,  ds = Initial reading of the dial gauge in mm and h = Initial height of the specimen in mm. The expansion ratio is used to evaluate the expansive nature of the soil.

b) Load penetration curve: The load obtained against each penetration reading is plotted with penetration in the X-axis. Normally the curve is convex upwards. But due to surface irregularities, the initial portion may convex downwards. A correction shall be then applied by drawing a tangent to the point of greatest slope. The point on the X-axis where the new tangent meets is considered as the origin of the load penetration curve. The points of 2.5 mm & 5 mm penetrations are shifted equal to the shift of the origin.

8.   Reporting of results

The CBR values are normally calculated for 2.5 mm and 5 mm penetrations.   California Bearing Ratio (CBR) = (PT/PS) x 100 where PT = Corrected load in kg for the selected penetration and  PS = Standard in kg for the corresponding penetration. The standard load for 2.5 mm depth penetration is taken as 1370 kg and for 5 mm depth penetration is 2055 kg. If the CBR for 5 mm penetration is higher than that for 2.5 mm penetration, the test is repeated. If the ratio is consistently higher for 5.0 mm penetration than for 2.5 mm, the ratio for 5.0 mm is reported as CBR of the material tested. 

The test data may be tabulated in the attached formats. The results of the test are presented as CBR value and expansion ratio. 

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