Rr420101 Advanced Foundation Engineering

Set No. 1

Code No: RR420101

IV B.Tech II Semester Supplimentary Examinations, May 2008 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) When the footing is subjected to eccentric loading, the load carrying capacity of footing may reduces, why? Explain clearly. (b) A rectangular footing of size 3 × 6 m is founded at a depth of 2 m in medium dense sand of angle of friction φ = 360 . The soil is submerged up to base level and is saturated above. The saturated unit weight of sand is 18 kN/m3 . Using Hansen method, determine ultimate bearing capacity for the following cases. i. The loading is vertical and symmetrical. ii. The loading is vertical and acts an eccentricity of 0.5m in both the length and width direction of the footing. iii. The loading is symmetrical but inclined at an angle of 200 to the vertical parallel to shorter side. Take for φ = 360 , Nq = 38 and Nγ = 40. [6+10] 2. (a) How does the settlement of a footing influence its design and how can a designer take into consideration the settlement of a footing? (b) A square footing 1.5m × 1.5m is founded at a depth of 1.0m in a deep deposit of dry sand. The average standard penetration penetration resistance of sand was found to be 20. The unit weight of sand is 18 kN/m3 . Estimate the settlement of the foundation due to a load of 500 kN acting on the footing. [10+6] 3. A friction pile group (4 × 3) consists of square piles having sides of 450 mm. The piles are 18 m long and are embedded in a normally consolidated clay deposit 26 m thick, followed by shale. The clay has an average cu value of 30 kN/m2 . The cu value at the pile base is 40 kN/m2 . The piles are spaced at 1.22 m centre-tcentre. Determine the load carrying capacity of the group using a factor of safety of 4. Assume the water table to be at the ground surface. What would be the settlement of the group, given that the saturated unit weight of clay as 19 kN/m3 , initial void ratio is 1.12 and the slope of the e- logp curve in the virgin compression portion is 0.24? [16] 4. (a) What is negative skin friction and its effect? How will you estimate the negative skin friction of group of piles? (b) A square pile group of 9 piles pass through a recently filled up material of 4.5 m depth. The diameter of the pile is 300 mm and the pile spacing is 0.9 m centre-to-centre. If the unconfined compressive strength of the cohesive material is 60 kN/m2 and unit weight is 15 kN/m3 , compute the negative skin friction of the pile group. [8+8] 1 of 2

Set No. 1

Code No: RR420101

5. (a) Describe various methods for the design of well foundations. What are their relative merits? (b) A circular well of 4.5 m external diameter and 3 m internal diameter is embedded to a depth of 10 m in a uniform deposit of sand (γsat = 19.8 kN/m3 , φ′ = 300 ). The well is subjected to a resultant horizontal force of 600 kN and a total moment of 4800 kN-m at the scour level. Compute the allowable equivalent resisting force due to earth pressure, applying a factor of safety of 2. Compute the maximum bending moment and determine its point of application when the well rotates at a certain point above the base. [10+6] 6. (a) With sketches differentiate between free earth support method and fixed earth support method. (b) An anchored sheet pile wall has a granular backfill whose density is 20 kN/m3 and φ = 330 , up to 5m depth. It is driven into cohesive soil (c= 20 kN/m2 and γ = 18kN/m3 ). The anchor is located at 1m below the surface. The water table is 2m depth below the top surface of the backfill. Using freeearth support method, determine the depth of penetration and force in the anchor. [8+8] 7. (a) What are the factors influencing the swell pressure of soil? (b) What are the tests available to determine the swell pressure of an expansive soil and explain any one of them very clearly? [8+8] 8. When are under-reamed piles used? Analyse a typical under-reamed pile and give the various design implications. [16] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR420101

IV B.Tech II Semester Supplimentary Examinations, May 2008 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Draw the bearing pressure diagram for an isolated footing under: i. ii. iii. iv. v.

Direct axial load Eccentric axial load Inclined and eccentric axial load Axial load and moment Axial load with moments in two directions.

(b) An isolated footing of dimensions L and B metres is subjected to a load P at ex and ey from its center of gravity. If the allowable bearing capacity of the soil below is q kN/m2 find P for ex = 0 and ey = 0.2B. [10+6] 2. (a) What are the types of settlements? Explain the method of estimation of immediate settlement in cohesionless soils using Schmertmann’s method. (b) A concrete footing 4m × 4m, is placed at a depth of 3m in a bed of stiff clay underlain by rock at 5m below the ground surface. The footing carries a net pressure of 150 kPa. The clay is overconsoildated. OCR= 3, and has mv = 0.08 m2 /MN and E= 55 MN/m2 . Estimate total, immediate and consolidation settlement? [10+6] 3. (a) Discuss the settlement of a pile group in sand with the help of settlement of an individual test pile data. (b) Discuss the settlement of pile groups in cohesive soils.

[8+8]

4. (a) What is down drag force on a pile? How to determine the down drag force in single piles and also in a group of piles? (b) A square pile group of 16 piles pass through a filled up soil of 3 m depth. The pile diameter is 250 mm and pile spacing is 750 mm. If unit cohesion of the material is 18 kN/m2 and unit weight is 15 kN/m3 , compute the negative skin friction on the group. [10+6] 5. (a) How to determine the safe load carrying capacity of a well foundation in different soils? (b) A circular well has external diameter of 7 m and is embedded in a sandy soil to a depth of 25 m below the maximum scour level. The submerged unit weight is 10 kN/m3 and φ is 350 . Resultant horizontal force= 1500 kN. Determine the allowable total equivalent resisting force due to earth pressure which can be adopted assuming the well to tilt: 1 of 2

Set No. 2

Code No: RR420101 i. about a certain point above the base and ii. about the base.

The well is subjected to a total moment of 30000 kN-m at the maximum scour level. [8+8] 6. (a) What are the differences between the anchored sheet pile wall with ‘free-earth support’ and the anchored sheet pile wall with ‘fixed-earth support’ ? (b) The height of a cantilever sheet pile from the top of the dredge level is 8 m. The water level in the backfill is 2 m from the top. The soil above the water table can be assumed to be dry. The saturated unit weight of the soil is 20 kN/m3 and the dry unit weight is 17.6 kN/m3 . The specific gravity of soil particles is 2.70. The coefficients of active and passive earth pressures are 0.33 and 3 respectively. Calculate the depth of penetration for a factor of safety of 1.0. [8+8] 7. Discuss the various laboratory methods of determining the swelling pressure and swelling potential of expansive soils. [16] 8. (a) Discuss the reactions that take place when soil is stabilized with lime and also discuss the various types of limes. (b) What is soil stabilization? Discuss the mechanism of soil stabilization. [8+8] ⋆⋆⋆⋆⋆

2 of 2

Set No. 3

Code No: RR420101

IV B.Tech II Semester Supplimentary Examinations, May 2008 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss the differences in Terzaghi and Meyerhof theories. Derive the expression of ultimate bearing capacity using Meyerhof’s approach. (b) Explain how to estimate the bearing capacity of shallow foundation when it is subjected to eccentric loads. [12+4] 2. (a) Explain the recommended construction practices to avoid detrimental differential settlement in large structures. (b) A clay layer 25m thick has a saturated unit weight of 19.2 kN/m3 . Ground water level occurs at a depth of 5m. It is proposed to construct a reinforced concrete foundation, 12.5m × 50m, on top of the layer, to transmit a uniform pressure of 150 kN/m2 . Determine the settlement at its centre, assuming that the void ratio drops from 0.725 to 0.700 due to loading. E for the clay is 30 MN/m2 . [8+8] 3. (a) How to estimate the settlement of pile groups in sandy soils? (b) Discuss in detail the settlement pile groups in cohesive soils.

[8+8]

4. (a) What do you understand by negative skin friction in pile foundation? Explain the situation which causes negative skin friction and explain how do you account for it in pile design. (b) A single under-reamed pile is installed in a deep deposit of stiff fissured clay. The diameter of the stem is 1.0 m and that of under-ream is 2.5 m. The length of the pile is 16 m. the unconfined compressive strength of clay is 140 kN/m2 . Estimate the allowable load carrying capacity of the pile for a factor of safety of 3.0. [8+8] 5. (a) Discuss the designing component parts of a well foundation in detail. (b) A circular well with external and internal diameter of 7 m and 5 m respectively is sunk in a sandy soil deposit to a depth of 20 m below the maximum scour level. The submerged unit weight of the deposit is 10 kN/m3 and its angle of internal friction is 350 . Due to an instantaneous, resultant horizontal force of 1000 kN, the well is subjected to a total moment of 15000 kN-m at the maximum scour level. Assuming the well to tilt about a certain point above the base, compute the allowable total horizontal equivalent resisting force for a factor of safety of 2.0. [10+6] 6. (a) How do you design the bulkheads by free earth support method? 1 of 2

Set No. 3

Code No: RR420101

(b) What are the different types of sheeting’s and bracing systems for braced cuts and describe them? [8+8] 7. (a) What is the cause of swelling in expansive soils? What are the tests available to identify expansive soils? Give the relative values. (b) Distinguish between differential free swell and swell potential. Discuss briefly the methods available to reduce swelling in soils. [8+8] 8. (a) Describe briefly the lime, cement and bitumen stabilization? (b) Discuss the principles and scope of soil-cement stabilization. ⋆⋆⋆⋆⋆

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[8+8]

Set No. 4

Code No: RR420101

IV B.Tech II Semester Supplimentary Examinations, May 2008 ADVANCED FOUNDATION ENGINEERING (Civil Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss the differences in Terzaghi and Meyerhof theories. Derive the expression of ultimate bearing capacity using Meyerhof’s approach. (b) Explain how to estimate the bearing capacity of shallow foundation when it is subjected to eccentric loads. [12+4] 2. (a) Write brief critical note on ‘settlement of foundations’ resting on different soils. (b) How to proportion the footings for equal settlements.

[10+6]

3. (a) Discuss the settlement of pile groups in sandy soils. (b) Design a pile group consisting of RCC piles for a column of size 650mm × 650 mm carrying a load of 5000 kN. The exploration data reveal that the sub-soil consists of deposit of soft clay extending to a greater depth. The other data of the deposit are: Compression index = 0.10, Initial void ratio = 0.9, Saturated unit weight = 19 kN/m3 , Unconfined compressive strength= 40kN/m2 . Also proportion the pile group for the permissible settlement of 50 mm. [8+8] 4. (a) Discuss the load carrying capacity of under-reamed piles. (b) An under-reamed bored pile is to be constructed in a stiff clay stratum. The diameter of the pile shaft and under-reamed base are 1 m and 3m, respectively. The pile is to extend from a depth of 2 to 20 m in the clay, the top under-ream bulb being at a depth of 18 m. The undrained shear strength of the soil is found to increase linearly from a value of 70 kN/m2 at 2m depth to 210 kN/m2 at 20 m depth from the surface. Determine the safe design load for the pile: i. to ensure overall factor of safety of 2; ii. a factor of safety of 3 under the base when shaft resistance is fully mobilized. Assume the value of adhesion coefficient α= 0.5.

[8+8]

5. (a) What are the various components of a well foundation? Discuss them in detail. (b) State the problems associated with well sinking and its remedial measures. [8+8] 6. Design an anchored bulkhead to support backfill of 6 m height above the level of dredge line. Both the soils below the dredge line as well as in the backfill are granular, having G= 2.7, e= 0.8 and φ = 300 . The ground water table is at a height of 3.5 m above the dredge line. Assume that: 1 of 2

Set No. 4

Code No: RR420101

(a) the anchor rod is at a depth of 1.5 m from the top of the backfill, (b) the desired factor of safety is 2.0.

[16]

7. (a) Define free swell index and differential free swell index and how to find out them? What is the normal range of values of differential free swell index for expansive soils? (b) Discuss the effect of swelling on building foundations.

[8+8]

8. (a) Describe the various steps involved in the process of soil stabilization using lime as additive. (b) What is sand cushion technique? How to use it in expansive soils? ⋆⋆⋆⋆⋆

2 of 2

[8+8]