An excavation is proposed for a site consisting of a homogenous, isotropic later of silt clay, 14.24 m thick, above a deep deposit of sand. The groundwater is 2m below ground level outside the excavation. The groundwater level inside the excavation is at the bottom. The void ratio of the silt clay is 0.62 and its Gs is 2.7. What is the limiting depth of the exacavation to avoid heaving? Assume artesian condition is not present.