JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year GEOTECHNICAL ENGINEERING Previous Question Paper (January/February - 2023 - R18)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Define air content and % air voids.
Answer
Air content (ac) is the ratio of the volume of air voids to the total volume of voids in a soil mass, expressed as a fraction or percentage. It is defined by the formula:
where Va is the volume of air and Vv is the volume of voids.
Percentage air voids (na) is the ratio of the volume of air voids to the total volume of the soil mass, expressed as a percentage. It is defined by the formula:
where V is the total volume of the soil sample.
A clay soil has liquid limit and plasticity index are 60% and 30% respectively. If the natural moisture content of clay is 40%, estimate its consistency index.
Answer
The consistency index (Ic) of a soil is defined as the ratio of the difference between the liquid limit and the natural moisture content to the plasticity index of the soil. It is calculated using the following formula:
Given the values:
- Liquid limit (wL) = 60%
- Plasticity index (Ip) = 30%
- Natural moisture content (wn) = 40%
Substituting these values into the formula:
The consistency index of the clay soil is 0.67.
Write the limitations of Darcy’s law.
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Write about piping phenomena beneath the dam.
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Why sheep foot rollers are used in clay soil compaction?
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An isolated footing is subjected to a load intensity of 160 kPa and its size is 1.5m×1.5m. By using 2:1 stress distribution method estimate the vertical stress in soil at a depth of 4m below the ground level.
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How do you identify over consolidated soil?
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Define degree of consolidation in terms of void ratio and pore water pressure.
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Write any two applications of shear strength of soils.
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A saturated clay has failed at a deviator stress of 130 kPa corresponding to a cell pressure of 0 kPa. Estimate the shear strength parameters.
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Part B
Explain two phase and three phase diagrams and derive from definitions:
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Explain liquidity index, consistency index, flow index and toughness index.
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What are the characteristics of flow nests? Discuss the uses of flow nets.
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What are factors affecting permeability of soil? Discuss.
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Write a brief note on the various types of rollers and their effectiveness with respect to compaction of different soil types.
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The following results were obtained in a compaction test. Determine the optimum moisture content and the maximum dry density by plotting the data.
| Moisture Content (%) | 7.4 | 9.7 | 10.5 | 11.5 | 13.1 | 14.4 |
|---|---|---|---|---|---|---|
| Bulk Unit Weight (kN/m3) | 18.81 | 20.07 | 20.52 | 21.06 | 21.06 | 20.07 |
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Discuss the variation of vertical stress along the vertical plane due to a Boussinesq’s point load.
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A raft of size 4m×4m carries a load of 120 kPa. Determine the vertical stress increment at a point 5 m below the centre of the loaded area using Boussinesq’s theory. Compare the result with that obtained by the equivalent point load method. Use the influence factor formula for vertical stress at corner point of rectangular area.
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Discuss the following: Over Consolidated Soil, Normally consolidated Soil and Under Consolidated Soil.
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Discuss the following: (i) Compression index and (ii) Effect of drainage on coefficient of consolidation.
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A soft normally consolidated clay layer is 10 m thick. The natural water content is 40%. The saturated unit weight of clay is 18.50 kN/m3; the grain specific gravity is 2.68 and the liquid limit is 60%. The vertical stress increment at the centre of the clay layer due to the foundation load is 15 kPa. The ground water table is at the surface of the clay layer. Determine the consolidation settlement of the foundation.
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Discuss the following: UU test, CU test and CD test.
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Discuss the merits of triaxial compression stress test over direct shear test.
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Sketch the stress-strain relationship for dense and loose sand. And write a note on critical void ratio.
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The following data relate to a triaxial compression tests performed on a soil sample. Estimate the shear parameters in terms of effective stress and total stress.
| Test | Cell pressure (kPa) | Deviator stress (kPa) | Pore water pressure (kPa) |
|---|---|---|---|
| 1 | 80 | 175 | 45 |
| 2 | 150 | 240 | 50 |
| 3 | 210 | 300 | 60 |
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