Abstract：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，such as intensity of loading，thickness of fine sand layer，angle of slope，and densification degree of sand，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 pore water is driven quickly because the permeability of the initial liquefied sand is larger than that of the origin sand，and that caused simultaneously settlement of the sand. Given that the drainage in the sand slope is along the maximum water pressure gradient (i.e. the direction perpendicular to the slope surface)，the sudden settlement of the surface of sand slope is observed. 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.
