Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III SOIL MECHANICS Previous Question Paper (March - 2024 - R16)
Note: Part A is compulsory (25 marks). In Part B, Answer any one question from each unit (50 marks).
Part A
Define the following terms: i) dry density, ii) submerged unit weight.
Answer
- Dry density (ρd): It is defined as the ratio of the mass of solids to the total volume of the soil mass. It represents the degree of densification of soil. ρd = Ms / V
- Submerged unit weight (γ'): Also known as buoyant unit weight, it is the unit weight of soil when it is below the water table, calculated as the difference between the saturated unit weight and the unit weight of water. γ' = γsat - γw
Sketch typical complete grain-size distribution curves for (i) well-graded soil and (ii) uniform silty sand.
Answer
- Well-graded soil: The grain-size distribution curve is smooth and covers a wide range of particle sizes, indicating a good representation of all sizes.
- Uniform silty sand: The curve is very steep, indicating that the soil particles are mostly of a similar size (poorly graded), with a small percentage of fines (silt).
What are the assumptions made in Darcy’s law?
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What is quick sand condition?
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Write down the Boussinesq equations of vertical pressure due to concentrated load.
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State any three assumptions of Westergaard’s theory.
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Define normally consolidated clay and over consolidated clay.
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Discuss Terzaghi’s theory of consolidation, stating the various assumptions and their validity.
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Explain the Mohr’s coulomb strength envelope.
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Explain briefly about Critical void ratio and Dilatancy.
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Part B
Answer the following:
The dry unit weight of a soil sample in the loosest state is 13.34 kN/m3 and in the densest state, it is 21.19 kN/m3. Determine the relative density of the sand when it has porosity of 33%. Assume the grain specific gravity as 2.68.
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Differentiate between Saturated density and Bulk density.
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Answer the following:
A sample of saturated soil has a water content of 25% and bulk unit weight of 20 kN/m3. Determine the dry unit weight, void ratio and the specific gravity of solids.
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What would be the bulk unit weight of the soil, if it is compacted to the same void ratio but has a degree of saturation of 90%?
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Answer the following:
The falling-head permeability test was conducted on soil sample of 4 cm diameter and 18 cm length. The head fell from 1.0 m to 0.40 m in 20 minutes. If the cross-sectional area of the stand pipe was 1 cm2, determine the coefficient of permeability.
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What is the critical gradient of a sand deposit of specific gravity = 2.65 and void ratio = 0.5?
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Answer the following:
Derive the expression for the critical hydraulic gradient.
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What are different methods for determination of the coefficient of permeability in the field? Discuss their limitations.
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Answer the following:
Explain in detail the construction of Newmark’s chart with an influence value of 0.005.
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Explain the concept of ‘Pressure bulb’ in soils.
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Two columns A and B are situated 6 m apart. Column, A, transfer a load of 500 kN and column B, a load of 250 kN. Determine the resultant vertical stress on a horizontal plane 2.0 m below the ground surface at points vertically below the points A and B. Use 2:1 stress distribution method.
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Answer the following:
There is a layer of soft clay 4 m thick under a newly constructed building. The overburden pressure over the center of the clay layer is 300kN/m2. Compute the settlement, if there is an increase in pressure due to construction of 100kN/m2. Take compression index, (Cc) = 0.50, specific gravity (G) = 2.70. The water content of the deposit was found to be 50%.
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Draw a typical time-consolidation curve for an increment of load and show the process of consolidation.
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Answer the following:
Differentiate between normally consolidated and over consolidated soils. How would you determine the over -consolidation pressure?
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What is coefficient of consolidation? What is its use in the settlement analysis?
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Answer the following:
Sketch the stress-strain relationship for dense and loose.
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Describe direct shear test. What are its merits and demerits?
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Answer the following:
The principal stresses at a point in a material are 80 kN/m2 and 40 kN/m2 determine the normal, shear and resultant stress on a plane inclined at 30 to the major principal plane. Find also, for this plane, the maximum value of obliquity.
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What are the factors affecting the shear strength of cohesive soils?
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