How does water table affect foundation design?

Water table significantly impacts foundation design: (1) Reduces effective stress and bearing capacity - submerged unit weight is about half of saturated weight, (2) Uplift pressure on foundation (buoyancy), requiring adequate dead load or anchoring, (3) Increases settlement due to reduced soil stiffness, (4) Requires dewatering during construction, (5) Potential for seepage and piping in excavations, (6) Corrosion risk for steel elements. Seasonal water table fluctuation must be considered using highest expected level.