A 10 m thick clay layer is underlain by a sand layer of 20 m depth (see figure below). The water table is 5 m below the surface of clay layer. The soil above the water table is capillary saturated. The value of γ_sat is 19 kN/m³. The unit weight of water of γ_w. If now the water table rises to the surface, the effective stress at a point P on the interface will