JNTU
JNTU B.Tech III SOIL MECHANICS Previous Question Paper (August - 2022 - R16)
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Main
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.
Answer
Given: γd,min = 13.34 kN/m3, γd,max = 21.19 kN/m3, n = 33% = 0.33, Gs = 2.68, γw = 9.81 kN/m3.
First, calculate the void ratio in the current state (e):
Calculate the current dry unit weight (γd):
Calculate the void ratios at the loosest (emax) and densest (emin) states:
Calculate the relative density (Dr):
What are the different types of soil structures which can occur in nature?
Answer
Soil structures are determined by the mode of deposition and the forces acting between soil particles. The primary types include:
- Single-grained structure: Typical of coarse-grained soils (sands/gravels) where gravitational forces dominate over surface forces, resulting in a dense or loose arrangement.
- Honeycombed structure: Found in fine sands and silts where surface forces cause particles to form an arch-like structure with large voids.
- Flocculated structure: Occurs in clays where net attractive forces between particles lead to a random, edge-to-face orientation.
- Dispersed structure: Occurs in clays where net repulsive forces cause particles to align parallel to each other, often due to remolding or chemical changes.
- Coarse-grained skeleton structure: A composite structure where larger particles form a skeleton and smaller particles fill the voids.
What are the pumping out methods for the determination of coefficient of permeability in the field? What are their advantages and disadvantages? What are Dupuit’s assumptions?
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The water table in a deposit of uniform sand is located at 2m below the ground surface. Assuming the soil above the water table is dry, determine the effective stress at a depth of 5m below the ground surface. The void ratio is 0.75 and specific gravity of solids is 2.65. If the soil above the water table is saturated by capillary action, what is the effective stress at that depth?
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What are the factors that affect compaction? Discuss in brief.
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With a sketch, explain the construction of Newmark’s chart.
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A line load of 100 kN/m extends to a long distance. Determine the intensity of vertical stress at a point 2m below the surface at a distance of 2m perpendicular to the line load. Use Boussinesq’s theory.
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Explain Westergaard’s theory for determination of the vertical stress at a point. How is it different from Boussinesq’s solution?
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What is field compaction? Briefly describe different methods of field compaction.
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Discuss Terzaghi’s theory of consolidation, stating the various assumptions and their validity.
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A 15m thick hydraulically isotropic clay stratum overlies an impervious stratum. If the coefficient of consolidation is 5 × 10-4 cm2/sec, find the time required for 50% and 90% consolidation (Tv = 0.20 and 0.85 respectively).
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Derive expression for the vertical stress distribution at a point due to load using Boussinesq’s theory.
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Explain effective stress equation for downward flow condition.
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What is Mohr’s circle? Discuss its importance characteristics.
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A Sample of dry cohesion less soil was tested in a triaxial machine. If the angle of shearing resistance was 30° and the confining pressure of 100 kN/m2, determine the deviator stress at which the sample failed.
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A shear vane, 7.5 cm diameter and 11.25 cm long, was pressed into soft clay at the bottom of a bore hole. Find the shear strength of the clay, if the torque required for failure was 40 N-m.
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Define critical void ratio. Explain the shear behavior of a soil whose void ratio is less than the critical void ratio.
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Explain Mohr-coulomb’s shear strength theory.
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