Soil investigation at a site gave the following information. Fine sand exists to a depth of 10.6 m and below this lies a soft clay layer 7.60 m thick. The water table is at 4.60 m below the ground surface. The submerged unit weight of sand \gamma_{b} is 10.4 \mathrm{kN} / \mathrm{m}^{3}, and the wet unit weight above the water table is 17.6 \mathrm{kN} / \mathrm{m}^{3}. The water content of the normally consolidated clayw_{n}=40 \%, its liquid limit w_{l}=45 \%, and the specific gravity of the solid particles is 2.78. The proposed construction will transmit a net stress of 120120 \mathrm{kN} / \mathrm{m}^{2} at the center of the clay layer. Find the average settlement of the clay layer.