ED – 790

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IV Semester B.E. (Civil) Degree Examination, December 2014/January 2015 (Semester Scheme) (2K6) CE-404 : BASICS OF SOIL MECHANICS Time : 3 Hours

Max. Marks : 100

Instructions : 1) Answering Questions no. 8 is compulsory. 2) Answer other four questions selecting one question each from Part A and Part B and two questions from Part C. 3) All main questions carry 20 marks each. 4) Assume missing data suitably. PART – A 1. a) What are Residual soils and Transported soils ? Explain the salient features of both the soils.

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b) Define: i) void ratio ii) porosity iii) water content.

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c) A soil sample with a moisture content of 15% is coated with paraffin wax of specific gravity of 0.9 displaced 135 CC of water and weighs 2 N. The weight of soil sample was 1.6 N. Given the specific gravity of soil solids as 2.7, find void ratio, porosity, bulk unit weight and dry unit weight.

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2. a) What is the smallest opening BIS sieve used in sieve analysis ? What is the basis for selecting that size ?

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b) With the help of particle size distribution curves, explain uniformly graded, well graded and gap graded soils.

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c) A sedimentation analysis by hydrometer was done with 50 g of oven-dried soil. The hydrometer reading in 1000 CC of soil suspension, 60 minutes after the commencement of sedimentation is 19.5. The effective depth for Rh = 20, is 12 cm from the calibration curve. The meniscus correction is +0.50 and composite correction is 2.50. Assuming G = 2.7 and viscosity of water as 0.007 poise. Calculate the smallest particle size which would have settled in the internal of 60 minutes and the percentage finer than this size. 10 P.T.O.

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PART – B 3. a) What is the purpose of soil classification ? How are soils classified as per BBIS classification system ? Explain briefly with smallest features and the plasticity chart. 10 b) Write briefly about structure of clay minerals Illite, Kaolinite and Montmorillonite with sketches.

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c) Differentiate between flocculated and dispersed structures seen in clay soils.

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4. a) Explain the variable head permeability test of derive the equation to determine the co-efficient of permeability of clayey soils of very low permeability in the laboratory. 10 b) Determine the average co-efficient of permeability in directions parallel and normal to the bedding planes of a stratified deposit of soil consisting of 3 layers of total thickness 3 M. The top and bottom layers are 0.5 M and 0.8 M thick. The values of K for the top, middle and bottom layers are 2×10–4 cm/sec, 3×10–3 cm/sec and 1×10–2 cm/sec respectively. 10 PART – C 5. a) Define compaction. Explain the factors which affect the compaction of soils. 10 b) Following results refer to a standard compaction test. Water content (%)

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10

14

20

25

Bulk density kN/M3

17.6

19.8

21

21.7

21.5

Determine the optimum moisture content and maximum dry density. Also determine the degree of saturation and percentage air voids at maximum dry density G = 2.7. 10 6. a) Distinguish between compaction and consolidation. b) What are curve fitting methods ? Describe the square root of time filling method.

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c) In a consolidation test, the co-efficient of consolidation was found to be 0.5×10–3m2/sec for a load increment of 20 to 40 kN/M 2. Determine the co-efficient of permeability of the soil if Ce = 0.25 and initial void ratio = 0.95. 10

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ED – 790

7. a) Distinguish between normally consolidation and over consolidated clays. What is their practical significance ?

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b) Describe the method of estimating pre-consolidation pressure of a soil deposit by conducting consolidation test on a sample from the same soil.

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c) A clay layer whose total settlement under a given load is expected to be 250 mm, settles by 50 mm at the end of 15 days after the applications of load increment. How many days will be required to reach a settlement of 25 mm ? How much settlement will occur in 300 days ? The layer has double drainage. 10 PART – D 8. a) Derive the relationship es = WG with usual notations.

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b) Why do we use a long-stem hydrometer in the soil laboratory ? Why is it marked only upto 1.03 g/cc ?

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c) What are Aquifers ? When is an aquifer called confined or unconfined ?

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d) Explain briefly how the compaction is controlled in the field.

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