Investigation On Mechanism Of Low-angle Landslide In Permafrost Regions Under Earthquakes

Qinghai-Tibet Plateau is one of the main permafrost region in China, and also one of the main seismic zone. With the development of the western regions, more and more large-scale construction projects are carried out in the Tibetan Plateau. Now, more attentions should paid to the construction and maintenance of such projects. So, it’s necessary to study the instability mechanism of the slope in permafrost regions, and it will be of significance influencing on the engineering construction.The shaking table test and numerical modeling method were used to study the mechanism of low-angle landslide in permafrost regions. Based on the results of the previous studies and site investigation, synthetic wave simulating the seismic characteristics in Qinghai-Tibet, the low-angle slope model with approximate prototype in permafrost region was completed, the shaking table tests were performed subjected to horizontal and vertical loading. The results show that the failure of low-angle slope model is characterized by complete slip along the interface between unfrozen soil and ice layer, while the deformation of soil in slope body does not occur. The horizontal natural frequency of vibration at the failure state decreased obviously while the vertical one does not change obviously compared with that of the initial state. The amplification of the acceleration along the slope increase with the elevation increasing, and the change is not obvious along the surface of the top slope before sliding, but obvious between the sliding and after that, and they are bigger subjected to the horizontal seismic loading than that of vertical one, in the soil-ice interface they are obviously smaller than that of the soil and ice layer. The pore water pressure increases obviously in soil-ice interface of the slope, which is sensitively affected by the horizontal seismic loading. During the vibration process, the temperature of the upper soil increased, and so did the moisture content at the unfrozen soil-ice layer. By numerical calculation on dynamic response of the slope under seismic loading, it pointed out that the safety factors of the slope decrease with the increasing of the vibration amplitude while the pore water pressure of the soil-ice layer increase, and the increasing is significantly when the vibration amplitude is large; The maximum shear strain mainly exists in soil-ice layer during the loading process. Considering all the factors, the existence of the soft soil-ice layer is the main factor of the slope sliding along the layer when an earthquake happens, and the increasing of excess pore water pressure, the water content and shear stress caused by the soft soil-ice layer are the inducing factors for the landslide in permafrost regions.This research was supported by the Open fund of State Key laboratory of frozen soil engineering(No.SKLFSE201209).