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IV B.Tech. I Semester Regular Examinations, November 2010GEOTECHNICAL ENGINEERING- II

(Civil Engineering )Time: 3 Hours Max Marks: 80

Answer any Five QuestionsAll Questions carry equal marks

*******1. (a) state the objectives of site exploration and explain the importance of the depth of

exploration for different structures(b) What is standard penetration number. Explain the procedure for determining it in

the field. Mention the corrections to be applied to the observed values of standard penetration number.

2. (a) Derive the expression for the factor of safety of an infinite slope in cohesive soils.(b) What will be the factor of safety of a 15 0 slope of infinite extent in a cohesion-

less soil whose angle of shearing resistance is 25 0?

3. A 10 m high wall retains dry gravel with a dry unit weight d = 22 kN/m 3. Show that for a trialwedge with a failure plane, passing through the toe of the wall, at 20 o to the vertical the

minimum force that the wall must provide is 212 kN/m, if for the gravel c = 0, = 38o

andbetween the gravel and the wall c w = 0, w = 32 o.

4. For the cantilever retaining wall shown in Figure, let the fallowing data be given:Wall dimensions: H = 5.4 m, x 1 = 0.45 m, x 2 = 0.75 m, x 3 = 1.20 m, x 4 = 1.80 m, x 5 = 0.85mD = 1.20 m, = 10 0.Soil properties: 1 = 18.5 kN/m 3, 1' = 34 0, 2 = 17.8 kN/m 3, 2' = 18 0, c2'= 50 kPa.Calculate the factor of safety with respect to overturning, sliding and bearing capacity.

Set No. 1Code No: M0121 / R07

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5. (a) What are the assumptions made in Terzaghi analysis of bearing Capacity?(b) A strip footing 1 m wide rests on the surface of dry Cohesion-less soil having

= 25 0 and = 1.8 t/m 3, what is the ultimate bearing capacity? What is its value if there as complete flooding Assume N = 10; N q =12.

6. The following are the results of a load settlement test carried out on a 30 cm X 30 cm plateinside a pit 3.5 m x 3.5 m x 1.2 m in sandy soil.

Load (kN) 4.0 10.0 15.0 20.0 25.0 30.0Settlement

(mm)

1.5 3.8 5.1 7.4 11.3 14.2

Design a spread footing for a column 450 mm x 450 mm in size carrying a vertical load of 1200 kN. The allowable settlement is 25 mm.

7. (a) Describe the procedure for the estimation of settlement of a pile group byconsidering only the frictional resistance of the pile group.


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(b) A group of 16 piles 25 m long and 450 mm in diameter is to be arranged in asquare form in a clay soil with an average unconfined strength of 36 kN/m 2.Workout the center to center spacing of the piles for a group efficiency factor of 1.Neglect bearing at the tip of the piles

8. (a) Discuss the IRC method for the design of Well foundations.(b) Sketch and List out the component parts of Well foundation and discuss about its

functions.

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Code No: M0121 / R07Set No. 1



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*******1. (a) What is the object of exploration program and list out the phases of the exploration

program and explain in brief?(b) Write short note on the depth of exploration and how can you fix the depth of boring in

different cases of foundations? i.e. Shallow and deep foundations.

2. A new canal is excavated to a depth of 5.5 m below ground level through a soil having c =14.3 kN/m 2, = 15 0, e = 0.8 and G = 2.80. The slope of the bank is 1:1. Calculate the factor of safety with respect to the cohesion when the canal runs full. If it is suddenly and completelyemptied, what will be the factor of safety? The stability numbers are as fallows: S n = 0.083 for450 Slope and = 15 0; Sn = 0.11 for u = 10

0 and S n = 0.138 for u = 50. Use linear

interpolation for the other values of u.

3.

A vertical gravity retaining wall, 12 m high, is to retain a clayey soil for which c u = 25 kN/m2

,u = 15 o and the bulk unit weight b = 19 kN/m 3. The soil surface is horizontal and level with

the top of the wall. The water table is horizontal and level with the bottom of the wall.Determine the magnitude and direction of the minimum force on the wall for a trial wedgewhose slip surface rises from the bottom of the wall at 70 o to the horizontal. Assume that theangle of wall friction is 10 o and the wall adhesion is 15 kN/m 2. Hint: You need to considerthe possibility of tension cracks.

4. A gravity retaining wall is shown in Figure. Calculate the factor of safety with respect tooverturning and sliding, given the fallowing data:Wall dimensions: H = 6 m, x 1 = 0.6 m, x 2 = 2 m, x 3 = 2 m, x 4 = 0.5 m, x 5 = 0.75 m, x 6 = 0.8m, D = 1.5 m.Soil properties: 1 = 16.5 kN/m 3, 1' = 32 0, 2 = 18 kN/m 3, 2' = 22 0, c2'= 40 kPa. Use theRankine active earth pressure in your calculations.

Code No: M0121 / R07 Set No. 2

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5. (a) How would you fix the depth of the foundation? Discuss the Rankines formulafor the minimum depth.

(b) Using Skemption theory, compute the bearing capacity of a square footing of 2 x 2 m,resting on the saturated clay at undrained condition at a depth of 1.5 m from the groundlevel. Depth correction factor, d c = 1 + 0.2D/B, shape correction factor, s c = 1 + 0.2 B/L,where D, B and L are the depth of foundation, width and length of the footingrespectively.

6. A soil deposit consists of 2 m of gravel overlaying an 8 m thick deposit of an over-consolidatedclay overlaying rigid permeable sandstone. The gravel has a unit weight of 22 kN/m 3 whensaturated and a unit weight of 18 kN/m 3 when dry. The properties of the clay are uniform

throughout the layer and indicated below: Void Ratio,e= 1.2; Specific Gravity,G s =2.7; Pre-consolidation pressure, 'pc=70 kPa; Compression Index,C c = 0.1; Recompression Index, C r = 0.02; Consolidation coefficient,c v=0.5 m 2 /year. Calculate the settlement under the centre of asquare tank of side 5 m exerting an average pressure of 175 kPa constructed on the groundsurface after a long period of time and estimate the time for 75% of this settlement to occur.Assume that initially the water table is at the surface of the gravel but that after construction it islowered to the surface of the clay. The clay should be divided into two equal sub-layers.


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7. (a) Differentiate critically in principles in deriving the Engineering News formulaand Hileys formula for Pile load capacity.

(b) What are the basis on which the dynamic pile formulae are derived?. Discusscritically the limitations of dynamic pile formulas.

(c) What will be the penetration per blow of a pile, which must be obtained indriving with a 3t steam hammer falling through 1 m allowable load, is 25 tones?

8. (a) Discuss the method of construction of well foundation and its sinking into theground. What are the cares to be taken, if there is a difference in level of sinkingof well during the construction?

(b) An open well 20 m deep is of cylindrical shape with external and internaldiameters of 9 m and 6 m respectively. If the water table is 2m below the top of the open well. Determine the minimum thickness of the seal required. Check forperimeter shear also. Assume c = 2400 kN/m 2; con = 24 kN/m 3(concrete).Allowable perimeter shear stress = 650 kN/m 2.


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*******1. (a) What are the major uses of boring program in soil exploration? Explain any one method

of boring and its suitability depending on the site conditions.

(b) Distinguish between the undisturbed and disturbed samples.

2. (a) Compute the factor of safety of an infinite slope in a cohesionless soil for a steadyseepage condition when the flow is parallel to the slope.

(b) The laboratory test gave the fallowing soil parameters: c = 40 kN/m 2, = 30 0. Theexpected parameters of the mobilized shearing resistances are c m = 25 kN/m 2 and m =220. The average effective pressure on the failure plane is 150 kN/m 2. Find the factor of safety with respect to the average shear strength, cohesion and angle of internal friction.

3. The figure below shows a 8 m high sea wall at a location where 4 m of sand overlie a deep claydeposit. The water table in the soil is at the same level as the sea level on the other side of thewall. Tests have been performed to determine the relevant soil properties. For the sand dry =17 kN/m 3, sat = 19 kN/m

3, and a series of shear box tests gave the following results at failure

Shear stress, (kN/m 2)

16 37 72

Normal stress, (kN/m 2)

20 50 100

A series of triaxial tests were performed on samples of the clayey soil ( sat = 16.5 kN/m2). This

has included 3 undrained unconsolidated tests in which pore pressures were measured and oneconsolidated undrained test. The stresses at failure are given below.


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Test type Cell pressure3

(kN/m 2)

Deviatorstress

1 - 3 (kN/m 2)

Pore pressureu

(kN/m 2)

Unconsolidated Undrained 0 50 -34.4Unconsolidated Undrained 50 50 15.6Unconsolidated Undrained 100 50 65.6

Consolidated Undrained 200 90 127.2By determining the soil strength parameters calculate, using Rankine's method, the minimum

force required to maintain the stability of the wall: (a) in the short term (b) in the long term

4. Check the stability of a cantilever concrete retaining wall having a stem thickness of 0.4 muniform throughout, 6.0 m height bed block thickness 0.8 m and a projection of 2.5 on theheel side and 1.5 m on the toe side. The unit weight of the wall material is 25 kN/m 3. The soilhas a unit weight of 18 kN/m 3 and an angle of internal friction of 36 0. Take in to account auniform surcharge on the ground of 50 kN/m 2. The ground level on the toe side is 1.2 m highabove the base of the wall.

Clay

Sea WaterSand

2 m

2 m

4 m

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5. A square footing has to carry a load of 1000 kN. Find the size of the footing for a factor of safety of 2.50. The depth of the foundation is 1.5 m. The soil has the fallowing properties: G= 2.60, e = 0.53, S = 0.50, = 30 0 and C = 10 kN/m 2. What will be the safe bearing capacityof the soil if the void ratio of the soil is 0.72 instead of 0.53. In this case find the size of thefooting and what will be the safe bearing capacity and size of the footing if the water tablerises to ground level. For = 30 0, Nc =30 N q = 18.4 N = 22.4.

6. (a) Differentiate between total settlement and differential settlement. What are the harmful

effects of differential settlements on structures? What are the possible remedial measures?(b) A rectangular footing 4 m x 2m exerts a pressure of 80 kN/m 2 on a cohesive soil (E s = 5.1

X 10 4 kN/m 2, = 0.50). determine the immediate settlement at the center assuming thefooting is (a) flexible (b) rigid. For flexible Influence factors for L/B = 2 are 1.53 at center

and 0.77 at corner. For rigid 0.8.

7. (a) From the cyclic pile load test the following data is obtained. Compute Skin frictionalresistance and Base resistance.

Load(tons)

0 1 3 5 7 8 10 15 25 35 50

Elastic

Settlement(mm)

0 16.97 22.33 24.23 25.43 25.93 26.81 28.69 32 35.15 39.75

(b) Compute the briefly outline how the load carrying capacity of a pile is determined in thefield. What are its limitations?

8. (a) What do you understand about the grip length? What is its importance in wellfoundations?

(b) Determine the outside diameter of an open well to be sunk through 40 m sand and waterto bed rock, If the allowable bearing capacity is 2000 kN/m 2. The well foundationreceives a load of 50 MN from the superstructure. The mantle friction is 30 kN/m 2. Testthe feasibility of sinking. Also calculate the thickness of the seal.


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5. A foundation 2.0 m square is installed 1.2 m below the surface of uniform sandy gravelhaving a density of 19.2 kN/m 2 above the water table and a submerged density of 10.1kN/m 3. The effective strength parameters are c 1 = 0 kN/m 2 and 1 = 30 0. Find the grossultimate bearing capacity for the conditions of water table well below the base (with rupturezone above the water table) Water table rising to the level of the base of the foundation andthe water table raises to the ground level. Use Meyerhof theory. The bearing capacity factors

are, = 30 0, Nq = 18.4 and N r = 15.7. Shape factors: S q = S r = 1+ 0.1 k p L B and d q =d r = 1 +

0.1 B D

k p , where k p = tan2(45+ /2).

6. A square footing has to carry a load of 1000 kN. Find the size of the footing for a factor of safety of 2.50. The depth of the foundation is 1.5 m in a dense sand deposit. The recordedSPT value at the foundation level is 20. The soil has the fallowing properties: G = 2.68, e =0.53, S = 0.10. The permissible settlement is 40 mm. Use IS code method.

Code No: M0121 Set No. 4

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7. (a) Write short note on(b) A group of 9 piles

ground level to a gr10 m respectively.piles were placed atgroup on the basis

8. (a) What do you undercontrol them.

(b) Discuss about the T

Code No: M0121 / R07

on the settlement of pile group.ith 3 piles in a row were driven into soft cl

eat depth. The diameter and the length of thehe unconfined compressive strength of the c90 cm center to center, compute the allowabf shear failure criteria for a factor of safety o

stand tilts and shifts in well foundations? Ex

erzaghi method of design of well foundation.

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y extending frompiles were 30 cm andlay is 70 kPa. If thele load on the pilef 2.5.

lain the measures to

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