JNTU
JNTU B.Tech II SOIL MECHANICS Previous Question Paper (April - 2018 - R13)
Note: This question paper contains two parts A and B. 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.
Part A
Explain the soil three phase diagram.
Answer
A soil mass is a three-phase system consisting of soil solids (particles), water, and air. The three-phase diagram represents these components as separate volumes (V_s, V_w, V_a) and weights (W_s, W_w, W_a), where W_a is assumed to be zero, simplifying the system to solids, water, and air.
Classify I.S soil classification.
Answer
The Indian Standard Soil Classification System (ISSCS) classifies soils based on grain size and plasticity characteristics:
- Coarse-grained soils: Gravel (G) and Sand (S), further subdivided by gradation (W, P) and fines (M, C).
- Fine-grained soils: Silts (M) and Clays (C), classified by plasticity (Low L, Medium I, High H) using the plasticity chart.
- Highly organic soils (Pt).
Give expression for vertical stress of a uniformly loaded circular area.
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Explain the concept of Boussinesq equation.
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Draw the Mohr circle of stresses.
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What are advantages of triaxial test?
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Differentiate between standard and modified compaction test.
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Define coefficient of consolidation.
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What is the difference between Rankine’s and Coulombs theories?
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Give the importance of Taylor’s stability number.
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Part B
What are index properties of soil?
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Give the classification of soils.
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Define the following:
Void ratio
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Porosity
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Specific gravity
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Soil structure
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Liquid Limit.
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Explain Westergaard’s theory for the determination of the vertical stress at a point.
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How is Westergaard’s theory different from Boussinesq’s solution? What are Boussinesq’s limitations?
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A rectangular foundation 3 m × 2m is perfectly flexible and carries a load of 300kN/m2. Determine the vertical pressure at a depth of 5m below a point P which is at a depth of 0.7m and a horizontal distance of 2.0m.
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There is a line load of 120kN/m acting on the ground surface along y axis. Determine the vertical stress at a point P which has x and z axis coordinates as 2m and 3.5m respectively.
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Explain about Mohr-Coulomb theory for stress analysis.
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Discuss the tests for shear strength of soils.
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The stresses on a failure plane in a drained test on a cohesionless soil are normal stress, σ=100kN/m2, shear stress, τ= 40kN/m2. Find the major and minor principal stresses and also the angle shearing resistance.
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Differentiate between compaction and consolidation.
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Discuss how quality control of compacted earth mass is ensured in the in-situ by using Proctor’s needle method.
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Discuss Terazaghi’s theory of consolidation, stating the various assumptions and their validity.
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A clay stratum 2.5m thick lies over a sandy stratum and has drainage on both sides. Calculate the values of the pore water pressure and the effective stress at the middle of the stratum when 60% consolidation has taken place under an increment of load from 500kN/m2 to 2500kN/m2.
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Discuss the Rankine’s earth pressure theory on passive earth pressure in cohesionless soils.
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A retaining wall is 7 m high, with its back face smooth and vertical. It retains sand with its surface horizontal. Using Rankine’s theory, determine active earth pressure at the base when the backfill is (i) dry, (ii) saturated and (iii) submerged, with water table at 2 m below the surface. Take γt=18 kN/m3, γsat=21 kN/m3 and ϕ=300.
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What is a stability number? What is its utility in the analysis of stability of slopes?
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Discuss the factors influencing the slope stability. What are the types of slope failures?
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