含弱透水夹层饱和砂土坡体滑坡的实验研究

TESTING STUDY ON LANDSLIDE OF SATURATED SAND SLOPE SANDWICHED WITH LOW-PERMEABILITY LAYER

通过含有细砂夹层的饱和砂土在冲击载荷下的滑坡模拟实验,考察了土层参数不均匀的坡面的滑坡模式,坡体变形,破坏和不均匀渗流引起的滑坡,特别是散体粒径不均匀时出现的含水层和通道与滑坡的关系,各控制参数(载荷的和土体的)对滑坡的影响,并对这类滑坡中的现象给出了定性解释。

The pattern of uneven seepage-induced landslide in the saturated sand slope sandwiched with a low-permeability layer under impact loading is explored by means of simulation tests. Especially, the relations between the development of landslide and the emergence of water layer and drainage pathway are described. Some major influencing factors are also examined. The testing results show that, under a certain impact loading, the structure of the sand sample undergoes irrecoverable deformation, the pore water pressure is built up immediately, and the sand sample is liquefied. The seepage is uneven in the sand sample because of the presence of the low-permeability layer (the thin fine sand layer). During the upward seepage process of the pore water in the liquefied sand, the pore water accumulates underneath the fine sand layer and thus the shear strength at that location becomes lower than that of neighboring region, providing that the liquefied sand still holds certain strength value. When the pore water accumulates and the shear strength beneath the fine sand layer is lost gradually, the sliding of the sand slope is initiated under the combining action of gravity and pore water pressure. The shear resistance and the sliding potential are determined by the sand sample and related to the location. The slope surface is separated into two parts because the lower reach of the sand slope undergoes a larger displacement relatively. The slide of the slope is damped, because the footing of the slope is elevated and the angle of the slope becomes smaller. A thin pore water seam can be observed just underneath the thin fine sand layer from the lateral side of experimental setup. The water flows along the water seam to form a drainage pathway and spills out at the fractured position of the upper surface of the slope. The whole process of the liquefaction, drainage, settlement, and sliding is a coupling one in which some fine sand may flush away and accumulate at the location with lower initial permeability. Under a certain intensive impact loading, the sand slope will experience the process described above. Therefore, the presence of the thin fine sand layer of lower-permeability in the sand slope is one of the important factors to cause this kind of landslide.