JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II SOIL MECHANICS Previous Question Paper (December - 2018 - R13)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.
Part A
Discuss about coefficient of curvature and coefficient of uniformity.
Answer
The Coefficient of Uniformity (Cu), defined as Cu = D60 / D10, represents the range of particle sizes in a soil sample. A value of Cu = 1 indicates a uniform soil, while higher values indicate a well-graded soil with a wide range of particle sizes.
The Coefficient of Curvature (Cc), defined as Cc = (D30)2 / (D10 × D60), describes the shape of the particle size distribution curve. For a soil to be considered well-graded, Cc typically falls between 1 and 3 for gravels and sands.
Write about principle of effective stress.
Answer
The principle of effective stress, proposed by Karl Terzaghi, states that the effective stress (σ') at any point in a soil mass is the difference between the total stress (σ) and the pore water pressure (u). It is expressed by the formula:
This principle is fundamental to soil mechanics because the shear strength and volume change behavior of soil are governed by the effective stress rather than the total stress. The total stress is the pressure exerted by the weight of the soil and any external loads, while the pore water pressure is the pressure of the water filling the voids between soil particles. As the effective stress increases, the soil particles are pressed more firmly together, increasing the frictional resistance and shear strength of the soil skeleton.
Write about vertical stress distribution diagrams on horizontal plane and vertical plane.
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Write about preparation of Newmark’s influence chart.
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Write about merits of laboratory tri-axial test.
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Write about stress systems with principal planes parallel to the coordinate axes.
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Write the basic assumptions for Terzaghi’s theory of one-dimensional consolidation.
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Write about mechanism of compaction.
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Write about basic modes of failure of slip surfaces.
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Write about earth pressure at rest.
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Part B
A deposit of fine saturated sand layer over a clay strata is 6 m in depth from the ground level. The water is 2 m below the ground level. If the bulk density of saturated sand below the water table is 18 kN/m3, calculate the effective stress at the top of the clay layer. Take G=2.67.
Answer
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Explain about the procedure to determine field density of soil by using sand replacement method.
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A square footing of size 4 m × 4 m carries a uniform load of 160 kN/m2. Estimate the stress increment at a point in the soil which is 4 m below the centre of the loaded area by using point load approximation method with four equivalent point loads.
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A line load of 70 kN/m run extends to a very long distance. Calculate the intensity of vertical stress at a point 3 m below the ground when the load is directly under the line load and at a distance 1.5 m perpendicular to the line. Use Boussinesq’s analysis for line load.
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Explain about determination of shear strength by laboratory vane shear test with a neat sketch.
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Explain about undrained strength obtained from unconsolidated undrained test by the laboratory tri-axial test with the help of neat sketch.
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Explain the laboratory procedure to determine coefficient of consolidation by using logarithm of time fitting method.
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A clay layer of 5 m thick is placed in between two highly permeable sand stratums. A sample of this clay layer is tested in laboratory for 50% of ultimate settlement in 12 minutes after the application of a certain pressure. How long will it take for a building proposed to be constructed at this site? Assume laboratory sample and the clay layer at the site are subjected to same increase of stress.
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Explain about Rankine’s theory of active earth pressure on retaining walls for cohesionless backfill with and without surcharge.
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A retaining wall of 6 m high has cohesionless backfill. The backfill has a void ratio of 0.67 and 0.32 in the loose and dense state and the related Ø is 24° and 42° respectively. Estimate active and passive earth pressure for both the cases. Take G = 2.6.
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