Engineering-related slope failure in permafrost regions of the Qinghai-Tibet Plateau

Thaw slumping existing on two slopes in permafrost region of the Qinghai-Tibet Plateau is studied with their geological features, deformations and ground temperature in this paper. The failure shows as collapse and slide of active layer along the massive ground-ice surface. The field-monitored data show that the retrogressively extending area, soil-body sliding velocity and the water content of the soils in the failed area strikingly change with the air temperature and slope facing aspect. On the south-facing slope, the values of all of these items are higher than that on the north-facing slope. The mean annual ground temperature in the failed area on the south-facing slope is evidently higher than that in the undisturbed natural ground and that in the north-facing slope. In addition, the input of heat into the permafrost below the sliding mass on the south-facing slope is more than the output. Therefore the permafrost in the slope processes degradation when landslide occurs. The genesis of this kind of slope failure is closely related to ice-rich frozen soils and activities of engineering cut. Based on static balance analysis, the stability estimating method for such landslide is presented considering the seepage of ice-melting ground water in the paper. At last, the engineering measures of preventing thaw slumping are proposed too.