SOIL PARTICLE SIZE DISTRIBUTION (GRADATION CURVE

Submission: 11/ 5

EXPERIMENT 1

SOIL PARTICLE SIZE DISTRIBUTION (GRADATION CURVE))

Standard Reference: ASTM D 422 – Standard Test Method for Particle-size Analysis of Soils or its British equivalent.

OBJECTIVE

This test is performed to determine the percentage of different grain sizes contained within a soil. The mechanical or sieve analysis is performed to determine the distribution of the coarser, larger-sized particles (gravel & sand), and the hydrometer method is used to determine the distribution of the finer particles (silt & clay).

THEORY

The main soil engineering properties are permeability, compressibility, and shear strength. The tests required to determine these engineering properties are generally elaborate and time-consuming. So, sometimes a geotechnical engineer may be interested to have a rough assessment of these engineering properties without conducting the abovementioned elaborate tests. This is possible if index properties such as soil particle-size distributions and others are determined.

EQUIPMENT REQUIRED

Balance; set of sieves; cleaning brush; sieve shaker; mixer (blender).

PROCEDURES (as per the British Standard)

1. Write down the weight of each sieve as well as the bottom pan to be used in the analysis. 2. Record the weight of the given dry soil sample (oven-dried sample – approximately 500 – 1000 grams).
2. Make sure that all the sieves are clean, and assemble them in the ascending order of sieve numbers (63 μm sieve at bottom). Place the pan below 63 μm sieve. Carefully pour the soil sample into the top sieve and place the cap over it.
3. Place the sieve stack in the mechanical shaker and shake for 10-15 minutes.
4. Remove the stack from the shaker and carefully weigh and record the weight of each sieve with its retained soil. In addition, remember to weigh and record the weight of the bottom pan with its retained fine soil.

DATA ANALYSIS

1. Obtain the mass of soil retained on each sieve by subtracting the weight of the empty sieve from the mass of the sieve + retained soil, and record this mass as the weight retained on the data sheet. The sum of these retained masses should be approximately equals the initial mass of the soil sample. A loss of more than two percent is unsatisfactory.
2. Calculate the percent retained on each sieve by dividing the weight retained on each sieve by the original sample mass.

• Calculate the percent passing (or percent finer) by starting with 100 percent and subtracting the percent retained on each sieve as a cumulative procedure.

1. Make a semi logarithmic plot of grain size vs. percent finer (or use a simple graph paper, as appropriate).
2. Compute Cc and Cu for the soil.
3. Determine the group name of the soil as per the BS standard.

DISCUSSION

Discuss the implication of your results; problems encountered and how you managed to solve that problem

CONCUSION

Provide some concluding remarks based on your results

Experiment 2: Field density test (soil bulk unit weight test)

Sand Replacement Method

Equipment:

1. Sand pouring cylinder
2. Calibrating container, 100mm diameter and 150mm height
3. Soil cutting and excavating tools, such as scrapper tool, bent spoon
4. Glass plate, 450mm square, 9mm thick
5. Metal container to collect excavated soil
6. Metal tray, 300mm square and 40mm deep with a hole of 100mm in diameter at the center
7. Weighing balance
8. Moisture content cans
9. Oven
10. Clean, uniform sand passing 1mm sieve and retained on 600 micron sieve in sufficient quantity.

Part-I: Calibration

Procedure:

1. Determine the internal volume of the calibrating container from the measured dimensions of the container.
2. Fill the sand-pouring cylinder with sand, within about 10mm of its top. Determine the mass of the cylinder + sand (M1) to the nearest gram.
3. Place the sand-pouring cylinder vertically on the calibrating container. Open the shutter to allow the sand to run out from the cylinder. When there is no further movement of the sand in the cylinder, close the shutter.
4. Lift the pouring cylinder from the calibrating container and weigh it to the nearest gram (M2(

5.Place the cylinder over a plane surface, such as a glass plate. Open the shutter. The sand fills the cone of the cylinder. Close the shutter when no further movement of sand takes place.

6.Remove the pouring cylinder and collect the sand left on the glass plate. Determine the mass of sand (M3) that had filled the cone by weighing the collected sand.

7. Determine the dry density of sand, as shown in the data sheet, Table-I.

Experiment: 3

Direct Shear Test

The general shear strength equation (Mohr-Coulomb failure criterion) in terms of effective stresses is  τ= c´+ σ´ tan φ´

where τ is shear strength, c’ is the effective apparent cohesion, υ’ is the effective angle of friction, and σ’ is the effective stress (σ – u) and subscript f represents shear stress at failure. For cohesionless soil (sand, gravel and some silt) the effective cohesion (c’) is zero and the shear equation reduces to  τ = σ´ tan φ´

The direct shear test set up consists of placing a soil sample in a split box having a cross-sectional area (A) and subjecting the test sample to a vertical normal load (N). Testing proceeds by displacing the lower half of the split box and measuring the horizontal shear forced (T) transmit through the soil to the upper portion of the box. Testing continues by displacing the lower box horizontally until the shear force increases to a maximum value and then decreases or remains essentially constant

Testing consists of determining the maximum shear for at least three test samples with three different applied normal stresses that are selected to be representative of anticipated field stresses.

Since a decrease in the sample void ratio will increase the soil internal angle of friction, test specimens are initially placed to the same density (unit weight). Shear strength parameters c’ and ϕ’ are determined by determining a best-fit line (y-intercept and slope) of the σ’f (abscissa) vs τmax (ordinate) plot.

Procedure

8. Repeat steps 1 to 7 for the other two samples and apply the appropriate normal load for each sample. Note the amount of compression of the sample when the normal load is applied; subtract this value from the original height of sample (if any).

Note that test is to be continued until a maximum reading on the load transducer has been passed and the readings have begun to decrease to a constant value. Do not continue the test past a horizontal displacement of 10 mm.

Shear box diameter = 60 mm

Required: Determine soil shear strength parameters (c’ and ϕ’) and use them in your Coursework Report

• Perform lab tests to generate data, which will aid them in identifying different types of soil and assess its strength to solve a soil settlement problem by evaluation of laboratory results; use appropriate geotechnical methods for analysis.
• Interpret laboratory-derived data for the design process and formulate an engineering approach to the solution of problems

REPORT CONTENT

OBJECTIVES AND THEORETICAL BACKGROUND

METHODS/PROCEDURES

ANALYSES/RESULTS/DISCUSSIONS

CONCLUSIONS