R5410101 Foundation Engineering

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Code No: R5410101

IV B.Tech I Semester(R05) Regular/Supplementary Examinations, December 2009 FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) What are the objectives of soil exploration and what data would be collected for a construction of twelve storeged RCC framed structure building. (b) Explain in detail the following Preliminary steps required for site investigations.

[8+8]

2. (a) For a c-φ soil, derive the equation for F.S. in infinite slope. (b) Derive the equation for F.S. for a purely cohesive soil by total stress analysis, which gives the stability of an embankment after its construction. [6+10] 3. (a) Obtain the equation for the total active earth pressure of a cohesive horizontal back fill on a vertical wall. (b) A retaining wall 6m high, with vertical back, supports a cohesive back fill having unit weight γ = 19kN/m3 apparent cohesion = 26 kPa; φ = 0. i. Calculate the internal pressure intensity at the top of the wall ii. Depth of tension crack iii. lateral pressure intensity at the base.

[8+8]

4. A retaining wall with a vertical smooth back retains Cohesionless back fill of height 6 m. The properties of the back fill are γ = 17 kN/m3 . The water table may raise up to top of the backfill. Initially its F.S. with out W.T. is 1.5. Find the F.S. after the W.T. rises to top level of wall. Against sliding and over turning. [16] 5. A load of 400 kN/m2 is carried by a strip footing, 2m wide, located at a depth of 1.5m in a clay soil with γsat = 20 kN/m3 . Water table is quite closed to the ground surface. Determine the factor of safety with respect to shear failure. (a) When cu = 10 kN/m2 and φ = 0 and (b) When c0 = 15 kN/m2 and φ0 =280 .

[16]

6. (a) Describe standard Penetration Test. What are its uses? (b) Discuss the effect of water tabel on the bearing capacity of the soil.

[8+8]

7. A 600 mm diameter pile is to be installed at a site that is characterized by two sand layers. The top layer is 12 m thick, has a γ = 20 kN/m3 and θ = 300 the bottom layer is 20 m thick, has a γ = 22 KN/m3 and θ =350 . The ground water table is of the ground surface. Compute the unit end bearing and the unit skin friction at depths of 10, 15, 20 and 25m below the ground surface. Use Nq = 20 for φ = 300 and Nq = 50 for φ = 350 . Take δ = φ and K = 1.0. [16] 8. What do you understand by the term ’efficiency of a pile group’ ? Derive the expression of spacing between friction piles for 100% efficiency of the pile group. [16] ?????

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Code No: R5410101

IV B.Tech I Semester(R05) Regular/Supplementary Examinations, December 2009 FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) State the various methods of soil exploration and explain in detail the penatration tests. (b) Draw a neat sketch of split spoon. Sampler showing all the salient parts.

[8+8]

2. (a) Derive the equation for F.S. for a purely cohesive soils slope stability of total stress analysis. (b) A vertical cut was made in a plastic clay having γ= 19kN/m3 . The cut was failed at a depth of excavation 4.5m. Determine the cohesive strength of clay. [6+10] 3. A smooth vertical back retaining wall is 6.5 high and retains a soil with γ = 18 kN/m3 andφ = 180 . The top of the soil is in level with the top of the wall and is horizontal. If the soil surface carries a u.d.l. of 4.5 kPa. Determine the total active earth pressure and its point of application. [16] 4. A masonry retaining wall of trapezoidal section is 6m high and 1m wide at top, retaining soil level with its top. Find the minimum base width of the wall to avoid tension at the base. γ of masonry is 23 kN/m3 and γ of the soil is 16kN/m3 ; φ =300 . The back face of the wall is vertical. [16] 5. A three- story building is to be constructed on a sand beach. Ground water rises to a maximum of 3m below ground level. The beach sand has the following properties: γd = 16.5 kN/m3 , φ = 320 .(Nc = 40, Nq = 25, Nγ = 30). The maximum column load will be 700 kN. Determine the sizes of footing for depths of 1m and 2m using a factor of safety of 3. Settlements are not to be considered. Evaluate the two alternatives of suitable foundation from practical consideration (difficulties of construction and cost). [16] 6. A footing 2.0m × 2.0m is located at a depth of 1.5m in a sand deposit. Borings have indicated that the average corrected N value at the site is 25. Water table is at a depth of 2m below the ground surface. Determine the net allowable bearing pressure for a factor of safety of 3 against shear failure and a permissible settlement of 25mm. used Teng’s equations. [16] 7. Write in detail the correlations for calculating: (a) End bearing resistances and (b) Frictional resistance of piles with SPT and CPT results.

[8+8]

8. What do you understand by the term ’efficiency of a pile group’ ? Derive the expression of spacing between friction piles for 100% efficiency of the pile group. [16] ?????

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Code No: R5410101

IV B.Tech I Semester(R05) Regular/Supplementary Examinations, December 2009 FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) State the various methods of soil exploration and explain in detail the penatration tests. (b) Draw a neat sketch of split spoon. Sampler showing all the salient parts.

[8+8]

2. (a) For a c-φ0 soil, derive an equation for F.S. by Swedish method of slices, describing to obtain the locations of most critical slip circle. (b) An embankment 6m high has a slope of a 1V : 2H. The soil has φ=300 . c = 5KPa and γ=19KN/m3 . A trial slip circle has a radius of 8.8m and its centre is at the same level as the top of the embankment the slip circle passes through the toe. Find the F.S. with respect to this slip circle by the method of slices. [8+8] 3. Describe in detail the Culman’s graphical method for Active and passive earth pressure determination on retaining wall. Give the procedure in steps for both the active and passive cases. [16] 4. Calculate the variation of stresses at the base of a masonry retaining wall with a top width of 2 m , bottom width 4 m and height 6 m. The face retaining the soil is vertical. The soil properties are c = 20 kPa, φ =300 ; γsat = 22 kN/m3 . Water table is 2 m below the top of wall. The coefficient of friction between base of wall and the soil is 0.3. Check the stability against sliding. [16] 5. (a) What is the function of a ‘foundation?? (b) Write in detail about the general types of foundations, with suitable sketches? [8+8] 6. A strip footing 1.2 m wide is located at a depth of 1.5 m in a non - cohesive soil deposit for which the corrected N - Value of SPT is 20. Water table is located at a depth of 2 m below ground surface. Find the allowable bearing pressure for the soil by. (a) Meyerhof’s equation (b) Terzaghi’s empirical relationship.

[16]

7. A concrete pile 16 m long and 410 mm × 410 mm in cross section. The pile is fully embedded in sand for which γ = 17 kN/m3 and φ1 = 300 . Calculate: (a) Given K = 1.3 & δ = 0.8 φ0 , determine the frictional resistance( fs ) (b) Estimate end bearing resistance by Meyerhof’s method. (c) Estimate allowable load - carrying capacity of the pile: Let FS = 4.

[16]

8. What do you understand by the term ’efficiency of a pile group’ ? Derive the expression of spacing between friction piles for 100% efficiency of the pile group. [16] ?????

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Code No: R5410101

IV B.Tech I Semester(R05) Regular/Supplementary Examinations, December 2009 FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) State the various types of penetration tests and explain in detail the SPT test with all corrections. [16] 2. (a) Explain in detail the Felonious method of locating centre of critical slip circle. (b) How many methods of testing could be made for the stability analysis of earth dam? Explain in detail the stability of upstrean and downstream slopes immediately after construction. [6+10] 3. (a) Differentate between Rankine’s and coulomb’s theories of earth pressures. (b) A retaining wall 4 m high retains cohesion less backfill; the ground surface sloping at an angle of 100 . (β) with the horizontal. The back of the wall is inclined to the vertical at a positive batter angle of 90 , γ= 19 kN/m3 , φ = 300 wall friction 120 . Determine the total active pressure by Coulomb’s method. [8+8] 4. A masonry retaining wall of trapezoidal section is 6m high and 1m wide at top, retaining soil level with its top. Find the minimum base width of the wall to avoid tension at the base. γ of masonry is 23 kN/m3 and γ of the soil is 16kN/m3 ; φ =300 . The back face of the wall is vertical. [16] 5. A square column transfers a load of 1650 kN on c-φ soil and rests on a soil which weighs 19 kN/m3 and has shear strength parameters as c = 10 kN/m2 and φ= 360 considering a factor of safety of 2.5, find the size of the footing if it is placed at the ground surface. Examine whether it would be cheaper to lower the footing to place it at the ground surface if the column is 450 mm2 and the footing is 500mm thick. The cost of concrete and the cost of excavation for hard soil at a site are Rs. 4,600 /m3 and Rs. 60/m3 , respectively. [16] 6. A footing, 2m square, is founded at a depth of 1.5 m in a sand deposit, for which the corrected value of N is 28. The water table is at a depth of 2m from the surface. Determine the net allowable bearing pressure, if the permissible settlement is 40 mm and a factor of safety of 3 is desired against shear failure. [16] 7. A concrete pile is 25 m long and 305 mm × 305 mm in cross section. The pile is fully embedded in sand for which γ = 17.5 kN/m3 and φ = 350 . Calculate: (a) The ultimate point load (QP) by Meyerhof’s method (b) The total frictional resistance. (For K = 1.3 and δ = 0.8 φ).

[16]

8. What do you understand by the term ’efficiency of a pile group’ ? Derive the expression of spacing between friction piles for 100% efficiency of the pile group. [16] ?????