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GATE 2022 CE (CE1) – Question 54

Geotechnical Engineering · Deep foundations: piles and pile groups · 2 marks · Numerical answer

A square concrete pile of 10 m length is driven into a deep layer of uniform homogeneous clay. Average unconfined compressive strength of the clay, determined through laboratory tests on undisturbed samples extracted from the clay layer, is 100 kPa. If the ultimate compressive load capacity of the driven pile is 632 kN, the required width of the pile is _______ mm. (in integer) (Bearing capacity factor Nc = 9; adhesion factor α = 0.7)

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Correct answer: 400

Explanation

For undrained clay, $c_u=q_u/2=50$ kPa. For square width B in metres, tip resistance is $9(50)B^2$ and skin resistance $\alpha c_u(4B)L=0.7(50)(4B)(10)$.

Thus $632=450B^2+1400B$. The positive root is B=0.4 m, verified by $72+560=632$ kN. **Width = 400 mm**.