Question

Please kindly answer the following question. It will be really kind if you answer all the question. Thank you.

1. Explain the importance of coefficient of curvature as you determine from the particle-size distribution curve.

2. A test group G1 compacts the soil in the compaction mould in 3 layers, giving 25 blows of rammer to each layer. Another test group G2 of your laboratory session uses 5 layers, giving 25 blows of rammer to each layer. How will the compaction test parameters (maximum dry unit weight and optimum water content) of the two groups vary?

3. Classify the soil according to USCS based on the following information:

Passing 75 µm = 10% ,Passing 4.75 mm = 70%, Uniformity coefficient = 8, Coefficient of curvature = 2.8 , Plasticity index = 4

4. Is it possible to get the specific gravity value using 3 weight measurements? Justify your answer.

5. Derive the analytical expression for the specific gravity of soil based on its basic definition.

6. Explain the importance of ZAV curve, and plot it for the soil as you see in your suburb.

7. In a liquid limit test, the crank of the Casagrande liquid limit device, as you see in the video demonstration of the test available at the BB unit site, is turned at the rate of 2 r/s so that the cup is lifted and dropped until the two parts of the soil come into contact along the bottom of the groove for a distance of 10 mm. A test group G1 followed this standard practice, but another test group G2 used 1 r/s. How do the liquid limit values vary? Explain briefly.

Answer 1

1. Coefficient of curvature is used to classify the soil as well graded and poorly graded. It is obtained from particle size distribution curve of soil from sieve analysis. It is denoted by CC.

For a well graded soil Cc should lie between 1 and 3.

Cc = (D30)^2/(D60×D10)

2. The soil in which degree of compactive effort will be more will be more compacted and corresponding dry density achieved will be more and optimum moisture content will be less as compared to the soil with low degree of compactive effort where dry density achieved less and optimum moisture content is more.

So, group G1 compacted the soil in 3 layers with 25 number of blows to each layer wher as group G2 compacted the soil in 5 layers with same 25 number of blows to each layer.

In both group test up to 3rd layer compactive energy was same so compaction will be same but as group G2 added another two layer so bottom layer is subjected to more compactive effort in next 50 blows when layer 4 and layer 5 was placed.

So in group G2 degree of compaction will be more and hence dry density will be more and corresponding optimum moisture content will be less and vice versa for froup G1.

3. Since, percentage passing 75 micron sieve is 10% which is less than 50% so it is a coarse grained soil with fine fraction.

Now, percentage passing 4.75 mm sieve is 70% which is more than 50% so the soil is sand.

Now, Cu > 6 and Cc = 2.8 which lies between 1 and 3. So the soil is well graded sand.

Now, percent finer is 10% which lies between 5% and 12% and pasticity index of soil i.e, Ip = 4 < 7 so it is silt.

So finally the soil is, well graded Sand with Silt i.e, SW-SM.

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