Civil Engineering > GATE 2026 SET-1 > Pile Foundation
A circular pile of 600 mm diameter and 6 m length is embedded in a saturated clayey soil. Undrained cohesion of the soil is 80 kPa. Unit weight of the soil is 19.20 kN/m3. The adhesion factor is 0.54. If the diameter of the pile is doubled to 1200 mm (keeping the length constant), the ratio of pile capacity of 1200 mm diameter pile to that of 600 mm diameter pile is ______ (rounded off to two decimal places).
Correct : 2.00
For a friction pile in clay, the pile capacity is governed by skin friction:
Q = α × c × π × d × L
The capacity is directly proportional to the pile diameter d through the perimeter term π × d. All other parameters — adhesion factor α, undrained cohesion c, and length L — remain unchanged when only the diameter is doubled.
For d₁ = 600 mm = 0.6 m:
Q₁ = 0.54 × 80 × π × 0.6 × 6 = 488.1 kN
For d₂ = 1200 mm = 1.2 m:
Q₂ = 0.54 × 80 × π × 1.2 × 6 = 976.2 kN
Ratio = Q₂/Q₁ = 1.2/0.6 = 2.00
The unit weight (19.20 kN/m³) given in the question is not needed for this calculation — end bearing is not considered for this friction pile problem, and the ratio depends only on the ratio of diameters.
Correct answer: 2.00 ✓
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