Among common foundation substrates, which has the highest bearing value?

• A. Bedrock
• B. Sand
• C. Clay
• D. Gravel

Answer: (A)

Understanding bearing value means knowing how much load a foundation base can carry safely without excessive settlement or failure. Bedrock provides the highest bearing value because it’s solid rock with extremely high shear strength and very little compressibility. Loads are transmitted through a stiff, stable base, so settlements are minimal.

Sand and gravel can offer good capacity when they’re well compacted and properly graded, but their strength depends on density, moisture, and how they’re laid down, so it’s more variable. Clay tends to have lower bearing capacity and more time-dependent settlement, especially when saturated, due to its cohesive and deformable nature.

In practice, while bedrock can have the highest bearing value, its actual capacity depends on rock quality and joints or fractures; engineers may design appropriate foundations (like rock sockets or piers) to use solid rock when available.