JNTU
JNTU B.Tech III GEOTECHNICAL ENGINEERING Previous Question Paper (July/August - 2023 - R13)
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
What is flocculated structure in soil?
Answer
A flocculated structure is a soil fabric typically found in fine-grained soils like clays, where individual particles are arranged in a random, edge-to-face or edge-to-edge orientation. This structure arises due to the dominance of attractive inter-particle forces over repulsive forces, often occurring in environments with high electrolyte concentrations or acidic conditions that compress the diffuse double layer.
Define specific gravity and write its use in soil mechanics.
Answer
Specific gravity of soil solids is defined as the ratio of the mass of a given volume of soil solids to the mass of an equal volume of distilled water at a specified temperature (usually 27°C). It is a dimensionless quantity.
In soil mechanics, it is primarily used to:
- Calculate the void ratio (e) when the degree of saturation, water content, and specific gravity are known, using the relationship Se = wG.
- Determine the unit weight of soil solids and the dry unit weight of the soil mass.
- Assist in the classification of soil and the evaluation of its permeability and seepage characteristics.
Write the formula for capillary rise in soil.
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What is effective stress principle?
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Differentiate standard and modified compaction.
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Draw the vertical stress variation under point load along horizontal axis at any depth.
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Draw the e-logp curve for normally consolidated clay.
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What is degree of consolidation? Write in terms of pore pressure.
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Why dense granular soils have more strength?
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When do you prefer UCS test on soil? Write its limitations.
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Part B
What is the use of classification of soils? Discuss Indian standard classification system?
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The following values of sand are given: D60 = 0.77 mm, D30 = 0.41 mm and D10 = 0.30 mm. Determine, Cu and Cc and state if it is a well graded or poorly graded soil?
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Liquid limit test on a given sample gave the following values. Plot the values on semi log-sheet and determine the liquid limit and flow index.
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Discuss the uses of consistency limits and relative density.
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A soil strata consist of 3 layers of thickness 1.5m, 1.5m and 2.5m having the coefficient of permeability of 1.2 × 10-2 cm/s, 1.5 × 10-3 cm/s and 1.3 × 10-3 cm/s respectively. Estimate the average co-efficient of permeability in the direction i) parallel to the bedding plane ii) normal to the bedding plane.
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Derive an expression to determine the coefficient of permeability of soil by laboratory constant head permeability test.
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Discuss the factors affecting permeability of soil in detail.
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A sample in a variable head permeameter is 80 mm in diameter and 100 mm high. The permeability of the sample estimated to be 10 × 10-3 mm/s. if it is desired that the head in the stand pipe should fall from 240 mm to 120 mm in 180 s, determine the size of the stand pipe which should be used.
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Derive an expression to determine coefficient of permeability of soil by laboratory falling head permeability test.
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An earth dam of 60 m wide is built on an impervious foundation with a horizontal filter at the base near the toe. The permeability of the soil in the horizontal and vertical directions is 4 × 10-2 mm/s and 1 × 10-2 mm/s respectively. The full reservoir level is 30 m above the filter. A flow net constructed for the transformed section of the dam, consists of four flow channels and 16 head drops. Estimate the seepage loss for the entire length of dam.
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A rectangular area of 3m × 6m carries a uniformly distributed load 120 kPa at ground surface. Find the vertical pressure at 4m below the centre and corner of the loaded area. Solve the problem by a) dividing the rectangle into four equivalent rectangles, and b) 2:1 method.
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Discuss Terzaghi’s theory of consolidation by stating the various assumptions and its validity.
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Describe square root time fitting method.
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Explain the procedure for determining pre consolidated pressure.
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An oedometer test is performed on a 2 cm thick clay sample. After 5 minutes, 50% consolidation is reached. After how long time would the same degree of consolidation is achieved in the field where the clay layer is 3.70 m thick? Assume the sample and the clay layers have the same drainage boundary conditions (double drainage).
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Describe the stress-strain, pore pressure and volume change behaviour of normally and over consolidated soils.
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What are the merits of triaxial compression stress test compared to other shear tests?
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What is shear strength of soil? Discuss the factors which effect the shear strength of cohesionless soils.
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The flowing test results are obtained from the direct shear test. Compute the shear strength parameters. Dimensions of the sample are 6 cm × 6 cm × 2 cm.
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