GATE 2018 CE (CE2) – Question 55
Nine piles form a 3×3 square group in dense sand beneath recently filled clay, as shown. Each pile perimeter is 126 cm, and group dimensions are 240 cm × 240 cm. Clay undrained strength is 15 kPa and unit weight 16 kN/m³. Negative frictional load on the group, to two decimals, is ______ kN.
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Correct answer: 472.00 to 472.50
Explanation
The keyed result uses the pile-group block convention. Downward block-side shear is $4(2.4)(2)(15)=288$ kN. Enclosed settling-clay weight is $2.4^2(2)(16)=184.32$ kN. Total is 472.32 kN. Summing individual pile shaft friction alone would represent a different model.