Bearing capacity of cohesive soil with surface crust

为了开发一种新的实验技术，利用该技术可以制作出由坚硬的界面壳覆盖的正常固结的粘土层。利用该技术进行了一系列的离心机模型试验，并用上限理论进行了承载能力预测。本研究得出了以下结论：1.两步固结法已被证明是非常成功的，用来制造具有表面结皮的正常固结的粘土；第一步-在搭接下逐层固结粘土浆液。底板减小固结压力。第二步-将固结的粘土倒置并将其固结在离心场中。当地壳强度较高时，其承载能力较高，特别是在地壳与正常固结粘土之间强度最低的界面区域发生较大变形。当壳面强度比(c&lt；U2&gt；)与界面强度(c&lt；U1&gt；)之比约为1/5时，随着地基宽度的增加，地基承载力变小。这一趋势与观察到的没有表面结壳的正常固结粘土层的趋势相反。通过上限计算得到的承载能力比实验值高出约30%，尽管理论上得到的破坏机制与观测结果吻合得很好。试验发现，承载力系数N_c随强度比c_&lt；U2&gt；/c_&lt；U1&gt；L的增大而增大，上限计算证实了这一结果。

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.