JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year FOUNDATION ENGINEERING Previous Question Paper (April - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
Define the area ratio.
Answer
The area ratio is a parameter used to quantify the degree of disturbance caused by a soil sampler during the collection of an undisturbed soil sample. It is defined as the ratio of the difference between the outer area of the cutting edge and the inner area of the sampling tube to the inner area of the sampling tube.
Where D_o is the outer diameter of the cutting edge and D_i is the inner diameter of the sampling tube. For a sample to be considered undisturbed, the area ratio should generally be less than 10%.
Describe standard penetration test.
Answer
The Standard Penetration Test (SPT) is an in-situ dynamic penetration test used to determine the relative density and shear strength parameters of cohesionless soils. The test involves driving a split-spoon sampler into the soil at the bottom of a borehole using a 63.5 kg hammer falling freely from a height of 760 mm.
The procedure consists of the following steps:
- The sampler is first driven 150 mm into the soil to seat it, and the number of blows required for this is recorded.
- The sampler is then driven two additional 150 mm increments, and the number of blows for each is recorded.
- The N-value is defined as the total number of blows required to drive the sampler through the final 300 mm of penetration, excluding the initial seating drive.
The resulting N-value is used in empirical correlations to estimate soil properties such as the angle of internal friction and allowable bearing capacity.
What are the assumptions made in Bishops theory?
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Discuss the factors leading to the failure of soil slopes.
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What are the assumptions in Coulomb’s theory?
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What is the practical significance of earth pressure theory?
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The load carrying capacity of end bearing pile is estimated as 100 kN. How the capacity can be doubled for the same length?
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State the factors affecting location of footing.
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Comment on well sinking.
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Write a note on shifts?
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Part B
Explain with neat sketch how dynamic cone penetration test is carried out in the field.
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If you are in-charge of subsoil exploration of important structures, how would you decide the depth of exploration? List out the factors you will consider and their importance.
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What are the assumptions that are generally made in the analysis of the stability of slopes? Discuss the factors leading to the failure of soil slopes. Also sketch the different types of slope failures.
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What is meant by infinite slope? What is the criterion for the stability of an infinite slope in sand?
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Define various factors of safety used in the analysis of stability of slopes.
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Explain about the construction of Culmann’s graphical method.
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Write a note on stability of earth retaining structures.
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A retaining wall has a smooth vertical back and is 8.5m in height. It retains a horizontal backfill of sand with φ = 33°. Find out the total active earth pressure per meter length of wall, if γ = 18 kN/m3 and γsat = 20 kN/m3
a) The water table is far below the base of the wall
b) The water table rises up to 4.0 m level above the base.
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How do you estimate the settlement of a footing on sand using plate load test? How is depth correction applied?
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The foundation for a Square footing of width 2m is to be founded at a depth of 1.5m. The soil properties are c=0, φ=36°, γ=18.2 kN/m3, γsat=20 kN/m3. Determine the net ultimate bearing capacity, when the water table is at i) 1 m below ground level ii) 1 m below foundation level (for φ=36°, Nc=52, Nq= 32 & Nγ=35)
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A bored concrete pile 30 cm diameter and 6.50 m length passes through stiff fissured clay subjected to seasonal shrinkage and swelling upto a depth of 1.50 m. The average undrained shear strength of clay is 50 kPa upto pile tip and 100 kPa below the pile tip. Find the ultimate load carrying capacity assuming adhesion factor of 0.3 and neglect the top 1.50 m soil.
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What considerations govern the fixing of the depth of a well foundation.
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What do you understand by grip length? What is its importance in well foundations?
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Briefly explain the procedure adopted in well sinking and bring out the problems that are encountered in open sinking.
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