Pile Foundations MCQ with answer and solution

Concept

Laterally Loaded Long Piles

Formula

Yes, the ultimate lateral load capacity (Qu) for a long pile is determined using Broms' formula based on the ultimate moment capacity (My) of the pile section, given by Qu = My / (e + zf), where e is the eccentricity of the applied load above the ground surface and zf is the depth to the point of maximum bending moment.

Step-by-step solution

- Identify the ultimate moment capacity (My) of the pile section. - Determine the eccentricity of the applied load (e) and the depth to maximum bending moment (zf). - Calculate the effective depth/lever arm by adding the eccentricity to the depth: (e + zf). - Divide the ultimate moment capacity by the effective depth: Qu = My / (e + zf).

Explanation

For a long, flexible pile under lateral loads, the pile bends significantly. Failure occurs when the bending moment exceeds the structural strength of the pile material, causing a plastic hinge to form and the pile itself to fail structurally before the soil along its entire length reaches its maximum capacity.

Shortcut

For laterally loaded piles: - Long pile = Pile/Structural failure (bends/breaks under load) - Short pile = Soil failure (rotates in soil without breaking)

Common mistake

Many students incorrectly select Option A or Option C (shear failure of the soil) because they confuse long flexible piles with short rigid piles, which fail due to soil resistance/shear failure, whereas long piles govern by structural bending failure of the pile itself.