What is the effect of the water table on the ultimate bearing capacity if its depth below the base of the footing is more than a certain multiple of the footing width?

The correct choice asserts that the water table has no effect on the ultimate bearing capacity if its depth below the base of the footing is more than a specific multiple of the footing width. This principle is rooted in geotechnical engineering and is particularly relevant when considering effects such as pore water pressure and effective stress in saturated soil.

When the water table is significantly below the footing, the soil above this level primarily contributes to the bearing capacity based on its effective stress, which is the stress carried by the soil skeleton. At such depths, the influence of pore water pressure is minimal, and the soil remains stable under typical loading conditions. As a result, the bearing capacity is primarily determined by the soil's shear strength rather than being adversely affected by the presence of water.

Thus, if the depth of the water table surpasses a certain ratio relative to the footing width, its influence on the soil's bearing capacity diminishes, allowing the soil to effectively support structural loads without significant concerns about buoyancy or strength reduction due to increased pore pressures. This emphasizes the importance of understanding soil mechanics principles when assessing foundation design and stability.

Understanding these dynamics is crucial when designing foundations, as it allows engineers to make informed decisions that ensure safety and performance under various conditions.