Test On Soil

                                                                    Test On Soil


There are lots of test which are to be done in soil for different purposes.If we are going to work in road we have to do LL-PI,GSA,FSI,CBR etc.When we are going to work in building project we have to do standard penetration test or plate plate load test for find the bearing capacity of the soil . Thats how at first it varies field to field.I have described some of the common test here ,if some of you are interested in it you can also ask me in the below comment Section.The some of common tests are -

1.Liquid limit test by Casagrande apparatus & Plasticity Index
2.Liquid limit test by Cone penetrometer
3.Grain Size analysis
4.Free SweLl Index
5.CBR Test

 1.   DETERMINATION OF LIQUID LIMIT- BY CASAGRANDE APPARATUS STANDARD
     IS: 2720 (Part 5) 1985.

DEFINITION  Liquid Limit is defined as the water content at which the soil changes from liquid state to plastic state.

APPARATUS
  Casagrande apparatus confirming to IS: 9259-1979.
  Grooving tool.
  Balance of capacity 500 grams and sensitivity 0.01gram.
  Thermostatically controlled oven with capacity up to 2500 C.
  Porcelain evaporating dish about 12 to 15cm in diameter.
  Spatula flexible with blade about 8cm long and 2cm wide.
  Palette knives with the blade about 20cm long and 3cm wide.  Wash bottle or beaker containing distilled water.
  Containers airtight and non- corrodible for determination of moisture content

 PROCEDURE
  Take representative soil sample of approximately 120gms passing through 425 micron IS sieve and mix thoroughly with distilled water in the evaporating dish to a uniform paste.
  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.
 Leave the soil paste to stand for 24 hours to ensure uniform distribution of moisture through out the soil mass.
  Remix the soil thoroughly before the test.
  Place a portion of the paste in the cup above the spot where the cup rests on the base, squeeze down and spread in to position with a few strokes of the spatula as possible and at the same time trim to a depth of 1cm at the point of maximum thickness.
  Make a clean, sharp groove by a grooving tool along the diameter through the centerline of the cam follower.
  Drop the cup from a height of 10 + 0.25 mm by turning the crank at the rate of two-revolutions/ sec, until the two halves of the soil cake come in contact with the bottom of the groove along the distance of about 12mm.
  Record the number of drops required to cause the groove close for the length of 12mm.
  Collect a representative slice of sample of soil approximately the width of spatula, extending from about edge to edge of the soil cake at right angle to the groove in to an air tight container and keep in the oven for 24hrs,maintained at a temperature of 1050 to 1100 C and express its moisture content as the percentage of the oven dried weight.
  Transfer the remaining soil in the cup to the evaporating dish and clean the cup and the grooving tool thoroughly.
  Repeat the operation specified above for at least three more additional trials (minimum of four in all) with soil collected in evaporating dish to which sufficient water has been added to bring the soil to more fluid condition
  In each case record the number of blows and determine the moisture content as before.                  The specimens shall be of such consistency that the number of drops required to close the groove shall not be less than 15 or more than 35.

REPORT

 Plot a flow curve with the points obtained from each determination on a semi logarithmic graph representing water content on the arithmetical scale and the no of drops on the logarithmic scale.
  The flow curve is a straight line drawn as nearly as possible through the four or more plotted points.
 The moisture content corresponding to 25 drops as read from the curve shall be rounded off to the nearest second decimal and is reported as liquid limit of the soil.

 PRECAUTIONS
 This test should proceed from the drier (more drops) to the wetter (less drops) condition of the soil.  This test may also be conducted from wetter to drier condition provided drying is achieved by kneading the wet soil and not by adding dry soil.

                   DETERMINATION OF PLASTIC LIMIT AND PLASTICITY INDEX

STANDARDS  IS: 2720 (Part-5) 1985.

OBJECTIVE  Plastic limit is defined as minimum water content at which soil remains in plastic state.

APPARATUS
 Porcelain evaporating dish about 12cm in diameter.
 Flat glass plate 10mm thick and about 45cm square or longer.
 Spatula flexible with the blade about 8cm long and 2cm in wide.
 Ground glass plate 20 x 15 cm.  Airtight containers.
 Balance of capacity 500grams and sensitivity 0. 01gram.
 Thermostatically controlled oven with capacity up to 250 0 C.
 Rod 3mm in diameter and about 10cm long.
 PROCEDURE
 Take representative soil sample of approximately 20g from the portion of the material passing 425 micron IS sieve and mix thoroughly with distilled water in an evaporating dish till the soil mass becomes plastic enough to be easily molded with fingers. In the case of clayey soils, leave the soil mass to stand for 24 hours to ensure uniform distribution of moisture through out the soil. Form a ball with about 8 grams of this soil mass and roll between the fingers and the glass plate as shown in Fig: 2.7.1 with just sufficient pressure to roll the mass into a thread of uniform diameter throughout its length. The rate of rolling shall be between 80 and 90 strokes/minute counting the stroke as one complete motion of the hand forward and back to the starting position again. Continue the rolling till the thread crumbles exactly at 3mm diameter. If the soil thread doesn’t crumble exactly at 3mm knead the soil together to a uniform mass and roll it again. Continue this process of alternate rolling and kneading until the thread crumbles under the pressure exactly at 3mm diameter. Collect the pieces of crumbled soil thread in an airtight container and determine its moisture content. Plastic limit test. Determine the plastic limit for at least two points of the soil passing 425 micron IS sieve.

REPORT  Report the individual and the mean of the results as the plastic limit of the soil to the nearest second decimal.

 PRECAUTIONS  At no time shall an attempt be made to produce failure at exactly 3mm diameter by allowing the thread to reach 3mm then reducing the rate of rolling or pressure or both and continuing the rolling with out further deformation until the thread falls a part.

PLASTICITY INDEX DEFINITION
 The plasticity Index is defined as the numerical difference between its Liquid Limit and Plastic Limit.

REPORT  Plasticity Index = Liquid Limit - Plastic Limit.

PRECAUTIONS
 In the case of sandy soils plastic limit should be determined first.
 When plastic limit cannot be determined the Plasticity Index should be reported as NP (Non-Plastic).
 When the plastic limit is equal to or greater than liquid limit, the plasticity index shall be reported as zero.

2.LIQUID LIMIT TEST OF SOIL USING CONE PENETROMETER METHOD

Cone Penetrometer

OBJECTIVE

For determination of the liquid limit of soil using cone penetrometer.

REFERENCE STANDARD

IS : 2720(Part 5)-1985- Methods of test for soils : Determination of liquid and plastic limit.

EQUIPMENT & APPARATUS

• Oven
• Balance (0.01g accuracy)
• Sieve [425 micron]
• Cone penetrometer

PREPARATION SAMPLE

After receiving the soil sample it is dried in air or in oven (maintained at a temperature of 600C). If clods are there in soil sample then it is broken with the help of wooden mallet.

PROCEDURE

1. About 150 gm. of air dried soil from thoroughly mixed portion of material passing 425 micron IS sieve is  obtained.
2. Distilled water is mixed to the soil thus obtained in a mixing disc to form a uniform paste.
3. Then the wet soil paste is transferred to the cylindrical cup of cone penetrometer apparatus, ensuring that no air is trapped in this process.
4. Finally the wet soil is leveled up to the top of the cup and placed on the base of the cone penetrometer apparatus.
5. The penetrometer is so adjusted that the cone point just touches the surface of the soil paste in the cup and the initial ready is to be taken.
6. The vertical clamp is then released allowing the cone to penetrate into soil paste under its own weight for 5 seconds. After 5 seconds the penetration of the cone is noted to the nearest millimeter.
7. The test is repeated at least to have four sets of values of penetration in the range of 14 to 28 mm.
8. The exact moisture content of each trial is determined

CALCULATION

• A graph representing water content on Y – axis and the cone penetration on X – axis is prepared. A best fitting straight line is then drawn.
• The moisture content corresponding to cone penetration of 20 mm. is taken as the liquid limit of the soil.

REPORT

The liquid limit is to be reported to the nearest first decimal place.

SAFETY & PRECAUTIONS

• Soil used for liquid limit determination should not be oven dried prior to testing.
• After mixing the water to the soil sample , sufficient time should be given to permeate the water throughout out the soil mass
• Wet soil taken in the container for moisture content determination should not be left open in the air, the container with soil sample should either be placed in desiccators or immediately be weighed.

                                       GRAIN SIZE ANALYSIS(IS 2720 PART-4)

OBJECTIVE

(a)Select sieves as per I.S specifications and perform sieving.
(b)Obtain percentage of soil retained on each sieve.
(c)Draw graph between log grain size of soil and % finer.

SCOPE OF EXPERIMENT

The grain size analysis is widely used in classification of soils. The data obtained from grain size distribution curves is used in the design of filters for earth dams and to determine suitability of soil for road construction, air field etc. Information obtained from grain size analysis can be used to predict soil water movement although permeability tests are more generally used.

APPARATUS

1.Balance,2.IS Sieves,3.Rubber pestle and mortar,4.mechanical Sieve Shaker

PROCEDURE

There are two types of method to do grain size analysis
1. Dry Sieving method
2.Wet Sieving method

Dry Sieving Method-

Dry the material and then sieve throug  100mm,75mm,19mm,4.75mm,2mm,425 mocron,75micron respectively and find weight the fraction retain on each sieve.Where above 4.75 mm(4.75mm to 80mm) sieve is known as Gravel,In between 4.75 mm to 75 micron is called Sand & 75 micron Passing Material is Known as Silt and Clay.

Alternative method

This method is generally adopted in the road projects where finer or filler material is used to construct embankment, sub-grade or confinement .

Here we have to divide the dry material in two parts by 4.75 mm sive and then the retain portion sieves through 100mm,75mm,19mm Sieve respectively and note the retain weight in each sieve then the material Passes through the 4.75 mm sieve is then passes through 75 micron sieve by washing the material until clear water is emitting off but if the material is cohesive in nature then we have to add some dispersing agent in water and the mix is put in a bowl with the material and left for some time.
then the retain portion of the IS 75 micron sieve is then oven dried and sieve through 2mm & 425 micron sieve and the retain weight is notted down.
By this method we can find the sand content,silt&clay content & also gravel content in a particular soil.

                                                      FREE SWELL INDEX


OBJECTIVE

To determine the free swell index of soil as per IS: 2720 (Part XL) – 1977. Free swell or differential free swell, also termed as free swell index, is the increase in volume of soil without any external constraint when subjected to submergence in water.


APPARATUS

i) IS Sieve of size 425µm 

ii) Oven

iii) Balance, with an accuracy of 0.01g

iv) Graduated glass cylinder- 2 nos., each of 100ml capacity

Procedure to determine Free Swell Index Of Soil

i) Take two specimens of 10g each of pulverised soil passing through 425µm IS Sieve and oven-dry.

ii) Pour each soil specimen into a graduated glass cylinder of 100ml capacity.

iii) Pour distilled water in one and kerosene oil in the other cylinder upto 100ml mark.

iv) Remove entrapped air by gently shaking or stirring with a glass rod.

v) Allow the suspension to attain the state of equilibrium (for not less than 24hours).

vi) Final volume of soil in each of the cylinder should be read out

REPORTING OF RESULTS

Free swell index = [V_d – V_k] / V_k x 100%
where,
V_d = volume of soil specimen read from the graduated cylinder containing distilled water.
V_k = volume of soil specimen read from the graduated cylinder containing kerosene.

OBJECTIVE

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

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

This instruction sheet covers the laboratory method for the determination of C.B.R. of undisturbed and remoulded /compacted soil specimens, both in soaked as well as unsoaked state

APPARATUS

1. Cylindrical mould with inside dia 150 mm and height 175 mm, provided with a detachable extension collar 50 mm height and a detachable perforated base plate 10 mm thick. 

2. Spacer disc 148 mm in dia and 47.7 mm in height along with handle. 

3. Metal rammers- Weight 2.6 kg with a drop of 310 mm (or) weight 4.89 kg a drop 450 mm. 

4. Weights. One annular metal weight and several slotted weights weighing 2.5 kg each, 147 mm in dia, with a central hole 53 mm in diameter. 

5. Loading machine. With a capacity of atleast 5000 kg and equipped with a movable head or base that travels at an uniform rate of 1.25 mm/min. Complete with load indicating device. 

6. Metal penetration piston 50 mm dia and minimum of 100 mm in length. 

7. Two dial gauges reading to 0.01 mm. 

8. Sieves. 4.75 mm and 20 mm I.S. Sieves.

9. Miscellaneous apparatus, such as a mixing bowl, straight edge, scales soaking tank or pan, drying oven, filter paper and containers. 

DEFINITION OF C.B.R.

It is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material.

C.B.R. = (Test load/Standard load )*100

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

PREPARATION OF TEST SPECIMEN

Undisturbed specimen

Attach the cutting edge to the mould and push it gently into the ground. Remove the soil from the outside of the mould which is pushed in . When the mould is full of soil, remove it from weighing the soil with the mould or by any field method near the spot.

Determine the density

Remoulded specimen

This is the general and preferable method where we have to cast a CBR mould by fillng the mould(2250cc) in 5 layers and giving 56 blows in each layer by 4.9kg rammer(in case of heavy compaction ) or by 2.6 kg rammer (in light compaction) then the mould is left into the water for 96 hours and then after soaking .

Dynamic Compaction

Take about 4.5 to 5.5 kg of soil and mix thoroughly with the required water.

Fix the extension collar and the base plate to the mould. Insert the spacer disc over the base (See Fig.38). Place the filter paper on the top of the spacer disc.

   Compact the mix soil in the mould using either light compaction or heavy compaction. For light compaction, compact the soil in 3 equal layers, each layer being given 55 blows by the 2.6 kg rammer. For heavy compaction compact the soil in 5 layers, 56 blows to each layer by the 4.89 kg rammer.

Remove the collar and trim off soil.

Turn the mould upside down and remove the base plate and the displacer disc.

Weigh the mould with compacted soil and determine the bulk density and dry density.

Put filter paper on the top of the compacted soil (collar side) and clamp the perforated base plate on to it. 

Static compaction

Calculate the weight of the wet soil at the required water content to give the desired density when occupying the standard specimen volume in the mould from the expression.

                                       W =desired dry density * (1+w) V

Where W = Weight of the wet soil

            w = desired water content

           V = volume of the specimen in the mould = 2250 cm³ (as per the mould available in laboratory)

Take the weight W (calculated as above) of the mix soil and place it in the mould.

Place a filter paper and the displacer disc on the top of soil.

Keep the mould assembly in static loading frame and compact by pressing the displacer disc till the level of disc reaches the top of the mould.

Keep the load for some time and then release the load. Remove the displacer disc.

The test may be conducted for both soaked as well as unsoaked conditions.

If the sample is to be soaked, in both cases of compaction, put a filter paper on the top of the soil and place the adjustable stem and perforated plate on the top of filter paper.

Put annular weights to produce a surcharge equal to weight of base material and pavement expected in actual construction. Each 2.5 kg weight is equivalent to 7 cm construction. A minimum of two weights should be put.

Immerse the mould assembly and weights in a tank of water and soak it for 96 hours. Remove the mould from tank.

Note the consolidation of the specimen. 

Procedure for Penetration Test

Place the mould assembly with the surcharge weights on the penetration test machine. (Fig.39).

Seat the penetration piston at the center of the specimen with the smallest possible load, but in no case in excess of 4 kg so that full contact of the piston on the sample is established.

Set the stress and strain dial gauge to read zero. Apply the load on the piston so that the penetration rate is about 1.25 mm/min.

Record the load readings at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 4.0, 5.0, 7.5, 10 and 12.5 mm. Note the maximum load and corresponding penetration if it occurs for a penetration less than 12.5 mm.

Detach the mould from the loading equipment. Take about 20 to 50 g of soil from the top 3 cm layer and determine the moisture content. 

Observation and Recording

For Dynamic Compaction

Optimum water content (%)                                                                      

Weight of mould + compacted specimen g                                               

Weight of empty mould g                                                                          

Weight of compacted specimen g                                                              

Volume of specimen cm³                                                                            

Bulk density g/cc                                                                                       

Dry density g/cc                                                                                         

For static compaction

Dry density g/cc

Moulding water content %

Wet weight of the compacted soil, (W)g

Period of soaking 96 hrs. (4days). 

For penetration Test

Calibration factor of the proving ring                                                1 Div. = 1.176 kg

Surcharge weight used (kg)                                                                2.0 kg  per 6 cm construction

Water content after penetration test %

Least count of penetration dial                                                             1 Div. = 0.01 mm 

If the initial portion of the curve is concave upwards, apply correction by drawing a tangent to the curve at the point of greatest slope and shift the origin (Fig. 40). Find and record the correct load reading corresponding to each penetration.

                                         C.B.R. = P_T/P_S  100

where P_T = Corrected test load corresponding to the chosen penetration from the load penetration curve.

          P_S = Standard load for the same penetration taken from the table I. 

Note :Generealy we find the CBR at 2.5mm and 5mm penetration then if the value of  CBR@2.5 is higher than the CBR@5 then the CBR@2.5 is reported as the CBR Value of the material if the CBR@5 is grater than CBR@2.5 the re test is required if after the 2nd time it is showing the same result then the CBR@5.0 is reported as the CBR Value of the material and this method is basically based on 100% Compaction .

If it is required to find out the CBR Value at 97%MDD then the metod is different where we have to cast three mould in different blows .

STANDARD LOADS

2.5mm (Pennetration)-1370 kg

5.0mm(Penetration)- 2055 kg

Hence CBR@2.5=(Load at 2.5mm Penetration/1370)*100

           CBR@5.0=(Load at 5.0mm Penetration/2055)*100