MOISTURE CONTENT TEST OF SOIL(IS-2720-PART-2-1973)

Moisture Cans

Objective

For determination of the moisture content of soil by oven drying method.

Equipment’s & Accessories

• Oven (105⁰C to 110⁰C min.)
• Metal container
• Balance (0.01 g accuracy)

Procedure

1. The number of the container is recorded, cleaned, dried and weighed.(W₁)
2. About 15-30 g of soil is placed in the container and the weight of soil with the sample is recorded.(W₂)
3. The can with the soil is placed in oven for 24hours maintained at a temperature 105⁰ to 110⁰C.
4. After drying the container is removed from the oven and allowed to cool at room temperature.
5. After cooling the soil with container is weighed.(W₃) 

Calculation

         
W₁=Mass of container, g
W₂=Mass of container and wet soil, g
W₃=Mass of container and dry soil, g

Report

The water content of the soil is reported to two significant figures.

Safety & Precautions

• Use hand gloves while removing containers from oven after switching off.
• The soil should be loosely placed in the bin, so as to allow easy evaporation of moisture
• Over heating should be avoided.
• Oven dry soil should not be kept open to the atmosphere (for cooling) as it may absorb moisture from atmosphere
• Ensure the identification number on the base and the lid of the bin is same

HOW TO DO UNCONFINED COMPRESSIVE STRENGTH TEST OF SOIL?

Unconfined Compressive Strength Test of Soil

Purpose

The primary purpose of this test is to determine the unconfined compressive strength, which is then used to calculate the unconsolidated undrained shear strength of the clay under unconfined conditions. According to the ASTM standard, the unconfined compressive strength (q_u) is defined as the compressive stress at which an unconfined cylindrical specimen of soil will fail in a simple compression test. In addition, in this test method, the unconfined compressive strength is taken as the maximum load attained per unit area, or the load per unit area at 15% axial strain, whichever occurs first during the performance of a test.

Standard Reference

ASTM D 2166 – Standard Test Method for Unconfined Compressive Strength of Cohesive Soil

Significance

For soils, the undrained shear strength (s_u) is necessary for the determination of the bearing capacity of foundations, dams, etc. The undrained shear strength (s_u) of clays is commonly determined from an unconfined compression test. The undrained shear strength (s_u) of a cohesive soil is equal to one-half the unconfined compressive strength (q_u) when the soil is under the f = 0 condition (f = the angle of internal friction). The most critical condition for the soil usually occurs immediately after construction, which represents undrained conditions, when the undrained shear strength is basically equal to the cohesion (c). This is expressed as:
s_u = c = q_u/2
Then, as time passes, the pore water in the soil slowly dissipates, and the intergranular stress increases, so that the drained shear strength (s), given by s = c + s‘tan ϕ’ , must be used. Where s‘ = intergranular pressure acting perpendicular to the shear plane; and s‘ = (s – u), s = total pressure, and u = pore water pressure; c’ and ϕ’ are drained shear strength parameters.

Equipment

• Compression device
• Load and deformation dial gauges
• Sample trimming equipment
• Balance
• Moisture can

Test Procedure

(1) Extrude the soil sample from Shelby tube sampler. Cut a soil specimen so that the ratio (L/d) is approximately between 2 and 2.5. Where L and d are the length and diameter of soil specimen, respectively.
(2) Measure the exact diameter of the top of the specimen at three locations 120° apart, and then make the same measurements on the bottom of the specimen. Average the measurements and record the average as the diameter on the data sheet.
(3) Measure the exact length of the specimen at three locations 120° apart, and then average the measurements and record the average as the length on the data sheet.
(4) Weigh the sample and record the mass on the data sheet.
(5) Carefully place the specimen in the compression device and center it on the bottom plate. Adjust the device so that the upper plate just makes contact with the specimen and set the load and deformation dials to zero.

Fig-1

(6) Apply the load so that the device produces an axial strain at a rate of 0.5% to 2.0% per minute, and then record the load and deformation dial readings on the data sheet at every 20 to 50 divisions on deformation the dial.
(7) Keep applying the load until (1) the load (load dial) decreases on the specimen significantly, (2) the load holds constant for at least four deformation dial readings, or (3) the deformation is significantly past the 15% strain that was determined in step 5.

Fig-2

(8) Draw a sketch to depict the sample failure.
(9) Remove the sample from the compression device and obtain a sample for water content determination. Determine the water content as in Experiment

Analysis

(1) Convert the dial readings to the appropriate load and length units, and enter these values on the data sheet in the deformation and total load columns.
(Confirm that the conversion is done correctly, particularly proving dial gage readings conversion into load)
(2) Compute the sample cross-sectional area A₀ = π*(d²)/4
(3) Calculate the deformation (ΔL) corresponding to 15% strain (e).
Strain (e) = ΔL / L₀
Where L₀ = Original specimen length (as measured in step 3).
(4) Computed the corrected area, A’ = A₀ / (1-e)
(5) Using A’, compute the specimen stress, s_c = P/A’
(Be careful with unit conversions and use constant units).
(6) Compute the water content, w%.
(7) Plot the stress versus strain. Show q_u as the peak stress (or at 15% strain) of the test. Be sure that the strain is plotted on the abscissa. (See fig-3)

Fig-3

(8) Calculate shear strength s_u as follows,
s_u = c (or cohesion) = q_u/2

SIEVE ANALYSIS OF SOIL(IS-2720-PART-4-1985)

Objective

For determination of particle size distribution of fine, coarse and all-in-aggregates by sieving. 

Reference standard

IS : 2720 (Part 4) – 1985 – Method of test for soil (Part 4-Grain size analysis)

Equipment & Apparatus:

• Balance
• Sieves
• Sieve shaker 

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. The sample is dried to constant mass in the oven at a temperature of 110⁰±5⁰C and all the sieves which are to be used in the analysis are cleaned.
2. The oven dry sample is weighed and sieved successively on the appropriate sieves starting with largest. Each sieve is shaken for a period of not less than 2 minutes.
3. On completion of sieving the material retained on each sieve is weighed.

 Calculation

The percent retained (%), Cumulative retained (%) & percent finer (%) is calculated.
Percent retained on each sieve = Weight of retained sample in each sieve / Total weight of sample
The cumulative percent retained is calculated by adding percent retained on each sieve as a cumulative procedure.
The percent finer is calculated by subtracting the cumulative percent retained from 100 percent.

Report

The result of the sieve analysis is reported graphically on a semi log graph, taking sieve sizes on log scale and % finer in arithmetic scale. The observation is maintained in observation sheet.

Safety & Precautions:

• Clean the sieves set so that no soil particles were struck in them
• While weighing put the sieve with soil sample on the balance in a concentric position.
• Check the electric connection of the sieve shaker before conducting the test.

LIQUID LIMIT TEST OF SOIL USING CASAGRANDE APPARATUS(IS-2720-PART-5-1985)

CASAGRANDE APPARATUS

Objective

For determination of the liquid limit of soil using casagrande apparatus.

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]
• Casagrande apparatus

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. The soil passing 425 micron sieve is used in this test.

Procedure

1. About 120 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 uniform paste. The paste shall have a consistency that would require 30 to 35 drops of cup to cause closer of standard groove for sufficient length.
3. A portion of the paste is placed in the cup of casagrande device and spread into portion with few strokes of spatula.
4. It is trimmed to a depth of 1 cm. at the point of maximum thickness and excess of soil is returned to the dish.
5. The soil in the cup is divided by the firm strokes of the grooving tool along the diameter through the centre line of the follower so that clean sharp groove of proper dimension is formed.
6. Then the cup is dropped by turning crank at the rate of two revolutions per second until two halves of the soil cake come in contact with each other for a length of about 12 mm. by flow only.
7. The number of blows required to cause the groove close for about 12 mm. is recorded.
8. A representative portion of soil is taken from the cup for water content determination.
9. The test is repeated with different moisture contents at least 3 times for blows between 10 and 40.

Calculation

• A ‘flow curve’ is to be plotted on a semi-logarithmic graph representing water content in arithmetic scale and the number of drops on logarithmic scale.
• The flow curve is a straight line drawn as nearly as possible through four points
• The moisture content corresponding to 25 blows as read from curve is the liquid limit of that soil

Report

The liquid limit is to be reported to the nearest whole number.

Safety & Precautions

• Soil used for liquid limit determination should not be oven dried prior to testing.
• In LL test the groove should be closed by the flow of soil and not by slippage between the soil and the cup
• 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.

PLASTIC LIMIT TEST OF SOIL(IS-2720-PART-5-1985)

Plastic Limit Test

Objective

For determination of the plastic limit of soil.

Reference Standard

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

Equipment & Apparatus

• Oven
• Balance (0.01 g accuracy)
• Sieve [425 micron]
• Flat glass surface for rolling

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. The soil passing 425 micron sieve is used in this test.

Procedure

1. A soil sample of 20 gm. passing 425 micron IS sieve is to be taken.
2. It is to be mixed with distilled water thoroughly in the evaporating dish till the soil mass becomes plastic enough to be easily moulded with fingers.
3. It is to be allowed to season for sufficient time, to allow water to permeate throughout the soil mass.
4. 10 gms. of the above plastic mass is to be taken and is to be rolled between fingers and glass plate with just sufficient pressure to roll the mass into a thread of uniform diameter throughout its length. The rate of rolling shall be between 60 and 90 stokes per minute.
5. The rolling is to be continued till the thread becomes 3 mm. in diameter.
6. The soil is then kneaded together to a uniform mass and rolled again.
7. The process is to be continued until the thread crumbled with the diameter of 3 mm.
8. The pieces of the crumbled thread are to be collected in a air tight container for moisture content determination.

Report

The Plastic limit is to be determined for at least three portions of soil passing 425 micron IS sieve. The average of the results calculated to the nearest whole   number is to be reported as the plastic limit of the soil.

Safety & Precautions

• Soil used for plastic 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.

DIRECT SHEAR TEST OF SOIL(IS-2720-PART-13-1986)

Shear Box Assemblies

Objective

Determination of shear strength parameters of a silty or sandy soil at known density and moisture content.

Reference Standards

IS: 2720(Part 13)-1986- Methods of test for soils: Direct shear test.

Equipment / Apparatus

• Shear box
• Box container
• Porous stone and grid plate
• Tamper, Balance , Sieve(4.75 mm)
• Loading frame, Proving ring, Dial gauge.

Preparation sample

One kg of air dry sample passing through 4.75mm IS sieve is required for this test.

Procedure

1. Shear box dimensions is measured, the box is set up by fixing its upper part to the lower part with clamping screws, and then a porous stone is placed at the base.
2. For undrained tests, a serrated grid plate is placed on the porous stone with the serrations at right angle to the direction of shear. For drained tests, a perforated grid is used over the porous stone.
3. An initial amount of soil is weighed in a pan. The soil is placed into the shear box in three layers and for each layer is compacted with a tamper. The upper grid plate, porous stone and loading pad is placed in sequence on the soil specimen.
4. The pan is weighed again and the mass of soil used is computed.
5. The box is placed inside its container and is mounted on the loading frame. Upper half of the box is brought in contact with the horizontal proving ring assembly. The container is filled with water if soil is to be saturated.
6. The clamping screws is removed from the box, and set vertical displacement gauge and proving ring gauge to zero.
7. The vertical normal stress is set to a predetermined value. For drained tests, the soil is allowed to consolidate fully under this normal load. (Avoid this step for undrained tests.)
8. The motor is started with a selected speed and shear load is applied at a constant rate of strain. Readings of the gauges are taken until the horizontal shear load peaks and then falls, or the horizontal displacement reaches 20% of the specimen length.
9. The moisture content of the specimen is determined after the test. The test is repeated on identical specimens under different normal stress values.

Calculation

• The density of the soil specimen is calculated from the mass of soil and the volume of the shear box.
• The dial readings are converted to the appropriate displacement and load units by multiplying with respective least counts.
• Shear strains are calculated by dividing horizontal displacements with the specimen length, and shear stresses are obtained by dividing horizontal shear forces with the shear area.
• The shear stress versus horizontal displacement is plotted. The maximum value of shear stress is read if failure has occurred, otherwise read the shear stress at 20% shear strain. The maximum shear stress versus the corresponding normal stress is plotted for each test, the cohesion and the angle of shearing resistance of the soil is determined from the graph.

Safety & Precautions

• Before starting the test, the upper half of the box should be brought in contact of the proving ring assembly.
• Before subjecting the specimen to shear, the fixing pins should be taken out.
• The rate of strain should be constant throughout the test.

DETERMINATION OF FIELD DENSITY OF SOIL BY CORE CUTTER METHOD (IS-27270-PART-29)

Aim

To determine the field density of soil by core cutter method

Reference

IS-2720-Part-29-Determination of dry density of soil in place by the core-cutter method

Apparatus

1. Cylindrical core cutter
2. Steel rammer
3. Steel dolly
4. Balance
5. Steel rule
6. Spade or pickaxe
7. Straight edge
8. Knife

Core cutter, Dolly & Rammer

Procedure

1. Measure the height (h) and internal diameter (d) of the core cutter and apply grease to the inside of the core cutter
2. Weigh the empty core cutter (W₁)
3. Clean and level the place where density is to be determined.
4. Drive the core cutter, with a steel dolly on its top, into the soil to its full depth with the help of a steel rammer.
5. Excavate the soil around the cutter with a crow bar and gently lift the cutter without disturbing the soil in it.
6. Trim the top and bottom surfaces of the sample and clean the outside surface of the cutter.
7. Weigh the core cutter with soil (W₂)
8. Remove the soil from the core cutter, using a sample ejector and take representative soil sample from it to determine the moisture content.

Precautions

1. Core cutter method of determining the field density of soil is only suitable for fine grained soil (Silts and clay). This is because collection of undisturbed soil sample from a coarse grained soil is difficult and hence the field properties, including unit weight, cannot be maintained in a core sample
2. Core cutter should be driven into the ground till the steel dolly penetrates into the ground half way only so as to avoid compaction of the soil in the core.
3. Before lifting the core cutter, soil around the cutter should be removed to minimize the disturbances.

Observations and Calculations

Calculate wet unit weight (γ_wet) of the soil using the following relationship
γ_wet = (W₂-W₁)/V
Where,
W₁ = Empty weight of core cutter
W₂ = Weight of core cutter + soil
V = Volume of core cutter (πd²h/4)
D = Inner diameter of core cutter
H = Height of core cutter