Abstract: This research focuses on the double-layer soft clay foundation with an upper soft layer and lower hard layer in Tianjin coastal area. The bearing property and failure mode of the double-layer soft clay grounds are studied by laboratory load test and numerical simulation. The results show that the P-S curves of double-layer soft clay foundation have an obvious concave-convex turning point due to the reinforcement effect of the underlying sedimentary soil, which is different from the reclaimed homogeneous ground. What’s more, the position of the turning point is closely related to the width-thickness ratio. The smaller the width-thickness is, the later the turning point appears, and the less significant reinforcing effect of underlying sedimentary soil is. Numerical results demonstrate that the failure modes of the double-layer soft clay grounds are trivially affected by the thickness of upper soft soil layer, all of them are general shear failure. The failure mode of the double-layer soft clay grounds varies from punch-shear failure mode to local shear failure mode with increasing the width of the load plate. When the width of the load plate is more than 3.0 m, the general shear failure mode occurs.

Key words: double-layer soft clay grounds, model test, bearing property, failure mode