Code No: RR Set No. 1

Transcription

1 Code No: RR Set No. 1 III B.Tech Supplimentary Examinations, Aug/Sep 2008 GEOTECHNICAL ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) A cylinder contains cu.m of loose dry sand which weighs 7.5 N. Under a static load of 200Kpa, the volume is reduced by 1 % and then by vibration it is reduced by 12% of the original volume. If the solid unit weight of the grains is N/ cu.m, compute the void ratio and bulk unit weight under the static load and vibrated load. (b) Explain what is Relative density and thixotropy and their use. [8+8] 2. (a) Explain the difference between compaction and consolidation. (b) Proctor compaction test was conducted on a soil sample, and the following observations were made: Water content,% Weight of wet soil,kg If the volume of the mould used was 950c.c and the specific gravity of soil was 2.65, Make necessary calculations and draw i. compaction curve and ii. 80% saturation line. [6+10] 3. (a) What is Stoke s law as applied to soils. (b) Describe the procedure used for doing hydrometer analysis for determining grain size distribution of fine-grained soils. [6+10] 4. (a) Mention two different methods of determining the permeability coefficient of a soil. Explain when you prefer each of them. (b) Write a note on factors affecting permeability. [8+8] 5. (a) Briefly explain the uses of flow net. (b) Derive an expression for seepage force per unit volume of soil interms of the hydraulic gradient and unit weight of water. [8+8] 6. (a) How would you determine the stresses at a point due to i. Strip load ii. Circular load. Compare the zones of influence due to the two types of loads. (b) A load of 16KN/m 2 is uniformly distributed over a circular area of 6m diameter at the ground surface. Calculate the vertical stress at a point P which is at a depth of 5m directly below the center of the loaded area. [10+6] 1 of 2

2 Code No: RR Set No (a) Describe a suitable procedure for determining pre consolidation pressure. (b) Explain secondary consolidation. (c) The total anticipated settlement due to consolidation of a clay layer under a certain. Pressure is 150 mm. If 45 mm of settlement has occurred in 9 months, what is the expected settlement in 18 months? [6+6+4] 8. The results of consolidated undrained triaxial test conducted on a soil sample are given below: Cell Pressure(kPa) Additional stress at failure(kpa) Pore pressure at failure(kpa) Find the shear strength parameters with respect to (a) total stress (b) effective stress [16] 2 of 2

3 Code No: RR Set No. 2 III B.Tech Supplimentary Examinations, Aug/Sep 2008 GEOTECHNICAL ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Prove from first principles, void ratio e is given by the expression γ d = G.γw 1+e where γ d is dry unit weight. (b) Soil A has dry density of 1.65g/cc (16.5 kn/m 3 ). Soil B has a dry density 1.75g/cc (17.5 kn/m 3 ). Both soils have G = 2.65, loose density 1.20 g/cc (12kN/m 3 ) and max density of 2 g/cc (20kN/m 3 ). Which soil is having higher relative density? Which soil has higher void ratio in natural state? [8+8] 2. (a) Briefly explain the factors affecting compaction. (b) A laboratory compaction test on soil having specific gravity 2.68 gave a maximum. Dry density of 1.82 g/cm 3 and a water content of 17 %. Determine the degree of saturation, air content and percentage air voids at the maximum dry density. What would be the theoretical maximum dry density corresponding to zero air voids at the optimum moisture content? [8+8] 3. (a) One kg of dry soil was subjected to sieve analysis. The mass of soil retained on each sieve is IS Sieve No. 2.00mm 1.40mm 1.00mm 500µ 250µ 125µ 75µ Mass,g Plot the grain size distribution curve and compute the % gravel, coarse sand, medium sand, fine sand and silt and also the Uniformity co-efficient. (b) What are index properties of soil? Why are they required? [8+8] 4. (a) What are the different types of soil water. Discuss. (b) The following data pertains to the coefficients of permeability of a stratified soil deposit. Soil Coefficient of permeability(mm/sec) Thickness of stratum(m) A B C Determine the ratio of coefficients of horizontal permeability to the vertical permeability. [8+8] 5. (a) Briefly explain the uses of flow net. (b) Derive an expression for seepage force per unit volume of soil interms of the hydraulic gradient and unit weight of water. [8+8] 1 of 2

4 Code No: RR Set No (a) How would you determine the stresses at a point due to i. Strip load ii. Circular load. Compare the zones of influence due to the two types of loads. (b) A load of 16KN/m 2 is uniformly distributed over a circular area of 6m diameter at the ground surface. Calculate the vertical stress at a point P which is at a depth of 5m directly below the center of the loaded area. [10+6] 7. (a) Bring out the points of difference between compaction and consolidation. (b) A normally consolidated clay layer of 10 m thickness has a unit weight of 20 kn/m 3 and specific gravity The liquid limit of the clay is 58%. A structure constructed on this clay increase the overburden by 10%. Estimate the ultimate consolidation settlement. There is no secondary compression. [8+8] 8. (a) Explain with a simple sketch, how triaxial compression test is conducted on a soil sample. (b) In an undrained triaxial test on a sample of saturated clay the cell pressure is maintained at 100 kpa. The unconfined compressive strength of the clay is 300 kpa. At what vertical stress in addition to cell pressure, should the sample fail? [10+6] 2 of 2

5 Code No: RR Set No. 3 III B.Tech Supplimentary Examinations, Aug/Sep 2008 GEOTECHNICAL ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Explain two fundamental building blocks of clay minerals. (b) Define specific surface of soils. How does it influence the engineering behaviour of soils. (c) Distinguish between adsorbed water and free water. [6+4+6] 2. (a) Explain the difference between compaction and consolidation. (b) Proctor compaction test was conducted on a soil sample, and the following observations were made: Water content,% Weight of wet soil,kg If the volume of the mould used was 950c.c and the specific gravity of soil was 2.65, Make necessary calculations and draw i. compaction curve and ii. 80% saturation line. [6+10] 3. (a) Explain laboratory method of determining Shrinkage limit of a given soil 08 (b) Soil A is silty sand and soil B is highly plastic clay, which soil will have higher i. Liquid limit ii. Shrinkage Limit iii. Void ratio iv. Natural Water content. Explain why? [8+8] 4. (a) What are the factors affecting the permeability of soil? Explain. (b) A constant head permeability test has been carried out on a soil sample, 10 cm in diameter and 15 cm long. With a hydraulic head of 30 cm, 300 c.c of water has been collected in 15 minutes time. Compute the coefficient of permeability of soil. [10+6] 5. (a) Write short notes on : i. critical hydraulic gradient ii. phreatic line (b) In a flownet the number of flow channels is 6 and the number of equipotential drops is 12. The co-efficient of permeability is cm/sec. Calculate the quantity of seepage under a head of 3m. [10+6] 6. (a) Derive the expression for vertical pressure due to a line load 1 of 2

6 Code No: RR Set No. 3 (b) A rectangular area 3 2mis uniformly loaded with load intensity of 150kN/m 2 at the ground surface. Calculate the vertical pressure at a point 3m below one of its corners by Newmark s chart. [8+8] 7. (a) The water table in a lake has been lowered by 20m below the bed, will this cause a settlement of a clay layer 5m thick, lying 25m below bed level? Explain. (b) An oedometer test is performed on a 2cm thick clay sample. After 5 minutes, 50% consolidation is reached. After how long a time would the same degree of consolidation be achieved in the field where the clay layer is 3.7m thick? Assume the sample and the clay layer have the same drainage boundary conditions (double drainage). [8+8] 8. (a) How is critical void ratio determined in the direct shear test? What is the significance of critical void ratio? (b) The following results were obtained from a direct shear test on specimens of sandy clay of cross section 60 mm 60 mm: Normal load,n Shear force at failure,n Find the shear strength parameters. If a triaxial test is carried out on a specimen of the same soil with a cell pressure of 120 kpa, find the deviator stress at which the failure would be expected. [8+8] 2 of 2

7 Code No: RR Set No. 4 III B.Tech Supplimentary Examinations, Aug/Sep 2008 GEOTECHNICAL ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Distinguish between Cohesive and non-cohesive soils. (b) While boring was done the soil sample was found to be saturated with kerosene oil. The saturated density of the soil is kg/m 3. Determine the void ratio and dry density if specific gravity for soil grain and kerosene oil were 2.65 and 0.89 respectively. [8+8] 2. (a) Explain the difference between compaction and consolidation. (b) Proctor compaction test was conducted on a soil sample, and the following observations were made: Water content,% Weight of wet soil,kg If the volume of the mould used was 950c.c and the specific gravity of soil was 2.65, Make necessary calculations and draw i. compaction curve and ii. 80% saturation line. [6+10] 3. (a) The Laboratory test on a particular sample of soil gave the following: Effective Size D 10 = 0.115, D 60 = 2.7 and D 30 = obtain the values of C c and C u. (b) Briefly explain the different Index properties of soils. [6+10] 4. (a) Explain the Phenomena of capillarity in detail. (b) In a falling head test the head fell from 300 mm to 100 mm in 800 seconds for a sample whose diameter was ten times that of stand pipe and whose length was 100mm. Find the coefficient of permeability. (Soil sample has a void ratio of 0.52). What would be your answer if void ratio is increased to [8+8] 5. (a) What is flow net? Draw a typical flow net for a homogeneous earth dam section and indicate the phreatic line. (b) A single row of sheet piles is driven upto a depth of 4m in a bed of clean sand having a co-efficient of permeability of cm/sec. An impermeable layer of very stiff clay exists at a depth of 10m below the G.L. The sheet pile wall has to retain water upto 4m above G.L. The height of water level on the down stream side is 0.5m. Construct the flow net and determine quantity of seepage loss considering unit width of the sheet pile. [8+8] 6. (a) How would you determine the stresses at a point due to i. Strip load 1 of 2

8 Code No: RR Set No. 4 ii. Circular load. Compare the zones of influence due to the two types of loads. (b) A load of 16KN/m 2 is uniformly distributed over a circular area of 6m diameter at the ground surface. Calculate the vertical stress at a point P which is at a depth of 5m directly below the center of the loaded area. [10+6] 7. (a) Distinguish between normally consolidated and over consolidated soils. (b) Explain in detail any one method for determining the coefficient of consolidation of soil. (c) The void ratio of a clay is 1.56, and its compression index is found to be 0.8 at Pressure of 180 kn/m 2. What will be the void ratio if the pressure is increased to 240 kn/m 2? [4+8+4] 8. (a) Derive the relation among major principal stress, minor principal stress and shear strength parameters at incipient failure condition. (b) An unconfined compression test was conducted on a saturated clay specimen 38 mm in diameter and 80 mm in height. The specimen failed when an axial load of 400 N was applied and the corresponding axial deformation was 7 mm. Find the unconfined compressive strength of the soil. When a triaxial compression test was carried out on a specimen of the same soil at a cell pressure of 100 kpa, the sample failed at a deviator stress of 400 kpa. Determine the shear strength parameters of the soil. [8+8] 2 of 2