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VTU Civil Engineering (Semester 5)
Geotechnical Engineering 1
June 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Derive an expression for the dry density of the soil in the form $\gamma_d = \dfrac { (1-n_1) G\gramma_w } {1+GW}$ with usual notations.
6 M
1 (b) Define the following with the help of three phase diagram. Indicate the units:
i) Water content
ii) Void ratio iii) Saturated unit weight iv) Degree of saturation.
8 M
1 (c) An embankment is to be constructed with a void ratio 0.85 and the quantity of embankment being 5000m3. Three borrow pits are available for the construction of the embankment and the corresponding void ratio and the cost of transportation for 1.0m3 of soil is given below. Determine the most economical borrow pit.
 Borrow Pit Void ratio e % Cost / m3 Rupees A 0.95 30 B 1.90 16 C 1.65 25
6 M

2 (a) What is consistency of soil? List and define consistency limits.
6 M
2 (b) Explain the following with the help of particle size distribution curve:
6 M
2 (c) In a liquid limit test on the clayey soil the following results are obtained:
Plot the Row curve and obtain
i) Liquid limit
ii) Plasticity Index if the plastic limit is 22%
iii) Flow Index
iv) Toughness Index.
 No. of flow 34 22 19 12 Water contents % 44.6 49.4 51.4 55.6
8 M

3 (a) Explain any two clay minerals with the help of neat sketches.
8 M
3 (b) Classify the soil on the basis of the following data as per IS 1498-1970.
 Soil Liquid limit % Plastic limit % Percent passing through 75 μ Percent gravel Percent sand Cu Ce A 400 45 100 0 0 - - B 40 20 70 10 20 - - C 40 20 20 20 60 7 2 D - Non plastic 10 10 80 5 10
12 M

4 (a) Explain briefly constant head permeameter test. Derive an expression to obtain coefficient of permeability under constant head condition.
8 M
4 (b) List and explain factors affecting the permeability of soil.
6 M
4 (c) In a falling head permeability test the length and area of cross section of soil specimen are 0.17m and 21.8×10-4m2 respectively. Calculate the time required for the head to drop from 0.25m to 0.10m. The cross sectional area of stand pipe is 2×10-4m2. The sample has three layers having permeabilities 3×10-5 m/s for first layer of 0.06m, 4×10-5 m/s for sectional 0.06m and 6×10-5 m/s for third 0.05 height. Assume the flow in taking place perpendicular to the bedding plane.
6 M

5 (a) What are the advantages and limitations of direct shear test?
6 M
5 (b) Explain the types of shear test based on different drainage conditions.
6 M
5 (c) A consolidated undrained test was carried out on a clay sample and the results are as follows.
Find total and effective shear parameters of soil.
 Cell pressure, kN/m2 100 200 400 600 Deviator stress at figure, kN/m2 300 410 610 850 Pore water pressure at failure kN/m2 -45 -15 +50 +110
8 M

6 (a) List the difference between standard and modified proctor compaction test.
5 M
6 (b) Briefly explain the use of proctor needle in field compaction control.
6 M
6 (c) On a compaction test following results are obtained
Volume of compaction mould is 95×10-4m3. Determine maximum dry density and OMC. Also plot zero air void line assuming the specific gravity of solids 2.65.
 Water content % 7.7 11.5 14.6 17.5 19.5 21.2 Weight of wet soil, N 16.67 18.54 19.92 19.52 19.23 18.83
9 M

7 (a) Explain Mass Spring Analog of theory of consolidation of soils.
7 M
7 (b) What is Pre-consolidation Pressure? How it is determined by Casagrande's method.
7 M
7 (c) List and brief explain the assumptions of one dimensional Terzaghi's theory of consolidation.
6 M

8 (a) Differentiate Compaction and Consolidation.
4 M
8 (b) Define Thixotropy and Sensitivity.
6 M
8 (c) The time to reach 40% consolidation of a two way drained saturated clay sample of 10mm thick in the laboratory is 40s. Determine the time required for 60% consolidation of the same soil 12m thick on an impervious layer subjected to same loading conditions as the laboratory sample.
10 M

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