The rise of water table below the foundation influences the bearing capacity of soil mainly by reducing

When the water table rises up to or above the foundation level, it alters these soil parameters in two main ways:
Reduction in Cohesion (C')
): Submergence or moisture increase significantly reduces or destroys the apparent cohesion (especially in fine-grained or partially saturated soils).
Reduction in Unit Weight (Y)
: The soil becomes submerged. This forces you to use the effective (buoyant) unit weight (Ysub) instead of the bulk or dry unit weight. This effectively cuts the soil's unit weight value roughly in half.
Friction Angle (phi): The effective angle of shearing resistance is an intrinsic shear strength parameter of the soil skeleton and remains largely unchanged by a simple rise in the static water table.