JUP – 084

*JUP084*

I Semester M.E. (Civil) (Geotechnical Engg.) Degree Examination, February 2014 (Semester Scheme) (2K8) Gt 104/EQ 104 : ADVANCED SOIL MECHANICS (Common to GT/EQ) Time : 3 Hours

Max. Marks : 100

Instructions : i) Answer any five full questions. ii) Missing data if any, may be assumed suitably.

1. a) What are clay forming minerals ? Briefly explain the structure of any two clay forming minerals.

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b) Explain the meaning of “Texture” and “Structure” of a soil.

6

c) Distinguish between “Black Cotton Soil” and “Laterite” from an engineering point of view.

6

2. a) Write an explanatory note on “Base exchange capacity” of soils.

6

b) What is diffused double layer ? Explain briefly the Guoy-Chapman diffused double layer theory.

6

c) Explain the following :

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i) X-ray diffraction analysis ii) SEM studies. 3. a) Discuss the effect of compaction of various engineering properties of soils.

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b) Explain the structure of soil samples along the compaction curve, as influenced by the varying compactive effort. c) Briefly discuss the factors influencing the shear strength of soils.

6 8 P.T.O.

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*JUP084*

4. a) What is Newmark’s influence chart ? Write a brief critical notes on this.

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b) Explain and construct the Newmarks chart with an influence value of 0.002. A raft foundation of size 4m x 4m carries a uniform load of 200 kPa. Using Newmarks, chart, calculate the stress increment at a point in the soil which is 4m below the centre of the loaded area. 14 5. a) Explain the shear strength characteristics of sand and normally loaded clays. b) Why is sand thought to be a “friction type” material ? Can saturated sand exhibit a φ = 0 ? If so under what circumstance ?

6

6

c) Two samples of a soil were subjected to shear tests. The results were as follows. σ3

(kPa)

100

300

σ1

(kPa)

240

630

If a further sample of the same soil was tested under a minor principle stress of 200kPa, what value of major principle stress can be expected at failure ? 6. a) Differentiate between shear strength parameters obtained from total and effective stress considerations. b) Define effective stress. Explain the concept of effective stress with the help of spring analogy.

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6

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c) A thin Layer of silt exists at a 18 m below the surface of the ground. The soil above thin level has an average dry density of 18 KN/m3 and an average water content of 30%. The water table is at the ground surface. Tests on undisturbed sample of silt indicated, Cu = 45 kPa, φ u = 18°, C1 = 36 kPa and φ′ = 27°. Estimate the shearing resistance of the silt on a horizontal plane, i) When the shear stresses builds up rapidly ii) When the shear stresses builds up very slowly.

8

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7. a) Differentiate between total settlement and differential settlement. How do they influence the design of a foundation ? Which one is critical from the design print of view ? Explain.

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b) A shallow foundation of size 3m x 3m, in plan, is resting in sand at a depth of 2 m (unit weight = 20 KN/m3) and exerts a pressure of 200 kPa. The variation of Young’s modules of soil with depth is as follows : Depth below GL : Es, kPa

2m

: 8,000

4m

6m

8m

10m

8,000

10,000

10,000

12,000

Estimate the immediate settlement of the foundation 5 years after the construction by using strain influence factor method. 8. Write notes on the following :

12 (5×4=20)

a) Pre-consolidation pressure. b) Pore-pressure co-efficients. c) Lambe’s compaction theory. d) Stress-strain behaviour of sand. e) Consolidatory settlement.

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