SOIL MECHANICS I ( SEMESTER - 5 )

Transcription

1 SOIL MECHANICS I ( SEMESTER - 5 ) CS/B.TECH (CE)/SEM-5/CE-501/07/(08) 1. Signature of Invigilator 2. Signature of the Officer-in-Charge Reg. No. Roll No. of the Candidate CS/B.TECH (CE)/SEM-5/CE-501/07/(08) ENGINEERING & MANAGEMENT EXAMINATIONS, DECEMBER 2007 SOIL MECHANICS I ( SEMESTER - 5 ) Time : 3 Hours ] [ Full Marks : 70 INSTRUCTIONS TO THE CANDIDATES : 1. This Booklet is a Question-cum-Answer Booklet. The Booklet consists of 32 pages. First page of the Booklet shows Instructions to the Candidates. The questions of this concerned subject commence from Page No a) In Group A, Questions are of Multiple Choi e type. You have to write the correct choice in the box provided against each questio b) For Groups B & C you ha e to answer the questions in the space provided marked Answer Sheet. Questions of Group B are Short answer type. Questions of Group C are Long answer type. Write on both si es of the paper. 3. Fill in your Roll No. in the box prov d d as in your Admit Card before answering the questions. 4. Read the instructions given inside carefully before answering. 5. You should not forget to write the corresponding question numbers while answering. 6. Do not write your name or put any special mark in the booklet that may disclose your identity, which will render you l able to disqualification. Any candidate found copying will be subject to Disciplinary Action under the relevant rules. 7. Use of Mobile Phone, Calculator or Log table is totally prohibited in the examination hall. 8. You should return the booklet to the invigilator at the end of the examination and should not take any page of this booklet with you outside the examination hall, which will lead to disqualification. 9. Rough work, if necessary is to be done in this booklet only and cross it through. No additional sheets are to be used and no loose paper will be provided Question Number Marks Obtained FOR OFFICE USE / EVALUATION ONLY Marks Obtained Group A Group B Group C Total Marks Examiner's Signature Head-Examiner/Co-Ordinator/Scrutineer

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3 3 ENGINEERING & MANAGEMENT EXAMINATIONS, DECEMBER 2007 SOIL MECHANICS I SEMESTER 5 Time : 3 Hours ] [ Full Marks : 70 GROUP A ( Multiple Choice Type Questions ) 1. Choose the correct alternatives for any ten of the following : 10 1 = 10 i) Soil in which some of the intermediate size particles are missing is known as a) poorly graded soil b) non-uniform soil c) ill proportioned soil d) skip graded soil. ii) The water content of a saturated soil is 50%. If the specific gravity of the solid is 2 4, its void ratio is a) 0 6 b) 1 2 c) 1 8 d) 2 4. iii) The natural void ratio of a sand sample is 0 6 and its density index is 0 6. If its void ratio in the loosest state is 0 9, then the void ratio in the densest state will be a) 0 2 b) 0 3 c) 0 4 d) 0 5. iv) The hydraulic head that would produce a quick condition in a sand stratum of thickness 1 5 m, specific gravity 2 67 and void ratio 0 67 is equal to a) 1 0 m b) 1 5 m c) 2 0 m d) 3 0 m.

4 4 v) The soils most susceptible to liquefaction are a) saturated dense sands b) saturated fine and medium sands of uniform particle size c) saturated clays of uniform size d) saturated gravels and cobbles. vi) Select the correct statement : a) The greater the viscosity, the greater is permeability b) The greater the unit weight, the greater is permeability c) The greater the unit weight, the smaller is permeability d) Unit weight does not depend upon permeabili y. vii) Which of the following methods is best suited for determination of permeability of coarse grained soils? a) Constant head method b) Falling head method c) Both of these d) None of these. viii) Quick sand is a a) type of sand b) flow condition occurring in cohesive soils c) flow cond tion occurring in cohesionless soils d) flow condition occurring in both cohesive and cohesionless soils. ix) Which of the following parameters have influence on permeability of soil? I. Void ratio II. III. IV. Degree of saturation Pressure head Grain size. Select the correct answer using the codes given below : Codes : a) I, II and IV b) II, III and IV

5 c) I, II and III d) I, III and IV. 5 x) Vertical stress on a vertical line at a constant radial distance from the axis of a vertical load a) is same at all depths b) increases with depth c) first increases, attains a maximum value and then decreases xi) xii) d) first decreases, attains a minimum value and then increases. The clay mineral with the largest swelling and shrinkage characteristics is a) Kaolinite b) Illite c) Montmorillonite d) none of these. The admixture of coarser particles like sand or silt to clay causes a) decrease in liquid limit and increase in plasticity index b) decrease in liquid limit and n change in plastic limit c) decrease in both liquid limit and plasticity index d) increase in both liquid limit and plasticity index. GROUP B ( Short Answer Type Questions ) Answer any three of the following questions. 3 5 = State and discuss the various factors that affect coefficient of permeability. 3. Define total, effective and pore water pressure in soil. 4. Establish the relationship : i c = G e, where G = specific gravity of soil particle e = void ratio, i c = critical gradient. 5. A constant head permeability test was carried out on a cylindrical sample of sand 10 cm dia and 15 cm height. 160 cm 3 of water was collected in 1 75 min, under a

6 6 head of 30 cm. Compute coefficient of permeability in m/year and flow velocity in m/sec. 6. The dry unit weights of sand in the loosest and densest states are respectively kn/m 3 and kn/m 3. Assuming the specific gravity of the solids as 2 67, determine the relative density of sand with porosity 30%. 7. In an oil well drilling project, drilling mud was used to retain the sides of the borewell. In one litre of suspension in water, the drilling mud fluid consists of the following materials : Material Weight ( gm ) Sp. Gravity Clay Sand Iron fillings Find the unit weight of the drilling f uid of uniform suspension. GROUP C ( Long Answer Type Questions ) Answer any three questions = a) Draw a Plasticity chart and explain its utility in the soil classification. b) The liquid and plastic limits of a given soil sample were 52 & 23 percents respectively. Classify the soil as per IS classification systems. c) A 1000 c.c. container was just filled with sand in its loosest possible state and then the container was filled at the densest possible state. The dry weights of sand, occupying the container space were 1520 gm and 1830 gm respectively. The sand in situ has a void ratio of If the specific gravity of the sand

7 7 particles is 2 65, determine the limiting void ratio and the relative density in situ a) A fully saturated clay sample has a volume of 65 c.c. and weighs 130 gm. After drying in oven at 105 C for 24 hrs., its weight reduced to 105 gm. Determine the specific gravity of soil solids, void ratio, porosity and dry density. b) The values of liquid limit, plastic limit and shrinkage limit of a soil were reported as below : W l = 60%, W p = 30% and W s = 20%. If a sample of this soil at liquid limit has a volume of 40 c.c. and its volume measured at shrinkage limit was 28 5 c.c., determ ne the specific gravity of the solids. What are the shrinkage ratio and volumetric shrinkage? c) Explain and discuss the significance of the values of uniformity coefficient and the coefficient of curvature a) What are Isobar and Pressure bulb? b) A long flexible strip footing of 2 5 m width having a smooth base, is subjected to a uniformly distributed load of 80 kn/m 2. Determine the vertical stress at a depth 2 m below the centre l ne of the footing. c) A trench is excavated in fine sand for a building foundation, upto a depth of 4 m. The excavation was carried out by providing the necessary side support for pumping water. The water levels at the sides and the bottom of the trench are shown in the figure below. Examine whether the bottom of the trench is subjected to quick sand condition if G = 2 64 and e = 0 7. If so, what is the remedy? dia

8 8 11. A 60 cm diameter well is being pumped at a rate of 1360 lt/min. Measurements in the nearby wells were made at the same time as follows : At a distance of 6 m from the well being pumped, the drawdown was 6 m and at 15 m the drawdown was 1 50 m. The bottom of the well is 90 m below the ground water table. Drawdown in the pumped well was m. Calculate (a) the coefficient of permeability, (b) the specific capacity of the well and (c) the rate at which maximum water can be drawn from this well a) A falling head permeameter accommodates a soil sample 6 m high and 50 cm 2 ross-sectional area. The sample of soil is made of three layers. The thickness of the first layer from top is 8 cm and has a value of k 1 = cm/sec, the thickness of second layer is 10 cm and has a valu of k 2 = cm/sec and the bottom layer of thickness 4 cm has k 3 = cm/sec. If it is desired that the head in the stand pipe should fall from 30 cm to 10 cm in 40 minutes, determine the size of the stand pipe. Assume that the flow is taking place perpendicular to the layers of the soil sample. b) Establish the relationship ( with neat sketch ) that is used in the above problem a) What are the as umpt ons made in Boussinesq s formula for stress distribution in soil? b) Two concentrated loads of 200 kn & 300 kn spaced at 5 metre act at the ground surface. Find the increase in the vertical stress at a depth of 5 metre below each load and also midpoint between load at the same depth. c) Explain Darcy s law and coefficient of permeability. d) Sand lying below a masonry dam has a porosity of 40% and a specific gravity of Find out the values of the critical hydraulic gradient END