Bearing capacity of cohesive soil with surface crust

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An attepmt was made to develop a new experimental technique with which a normally-consolidated clay layer overlain by hard syrface crust can be made. A series of centrifuge model tests was carried out using this technique and the bearing capacities were predicted by the upper-bound theory. Following conclusions were obtained from this study.1. The two-step consolidation has proven to be very successful for making normally-consolidated clay with surface crust; lst step --- To consolidate clay slurry layer by layer under the lap. floor reducing the consolidation pressures. 2nd step --- To turn upside down the consolidated clay and consolidate it in centrifugal field.2. The bearing capacitites are higher when the strength of the crust is higher and particularly large deformations take place in the area of the interface between the crust and nomally-consolidated clay where the strength is lowest.3. When the ratio of the strength at the crust surface(c_<u2>) to that at the interface(c_<u1>) is around 1/5, the bearing capacities become smaller with the increase of the width of footings. This trend is opposite to that observed for normally-consolidated clay layers without surface crust.4. Bearing capacities calculated by the upper-bound calculations are approximately 30% higher than the experiments, although failure mechanisms theoretically obtained agree fairly well with the observations. It has been found experimentally that the bearing capacity factor N_c increases with the strength ratio c_<u2>/c_<u1>l. The upper-bound calculations confirms this result.