奉节白衣庵老苍屋新滑坡成因分析

Analysis of mechanism of a new landslide in Fengjie, Chongqing, China

通过对奉节白衣庵古滑坡体上发生在老苍屋附近的新滑坡的现场调查、地质钻孔勘探以及降雨坡面产流的调查情况,结合对滑坡边界的演化、渗入坡体水的软化作用等因素的分析,阐明了该滑坡发生的主要原因是降雨产流汇聚形成冲沟,而冲沟对坡体坡角的不断下切使其逐渐丧失了支撑。此外,降雨坡面的入渗增加了上覆荷载以及土石介质遇水软化的效应,也是滑坡发生的原因之一。滑坡前缘的冲沟坡降急剧下切也为滑动的持续提供了客观的地质条件。最后,对滑后坡体的治理方案进行出了初步地探讨。

A new landslide occurred on July 22, 2003 in Fengjie, Chongqing, China. This new landslide is developed on Baiyi'an ancient landslide on which many old and new landslides exist. Because the landslide group is on the right left side of Yangtse River, once the hazard happened, it would be dangerous for not only the residents living on the slope but also the highway just through the landslide group, the docks along the river, and the normal running of the reservoir of the Three Gorges. Therefore, attention should be given to the landslides which occur possibly in the future and some measures must be taken. In this paper, the mechanism of the new landslide is analyzed after detailed surveying on the debris for the runoff and infiltration on the slope, the slope boundary, and its geological condition by drilling. Combining the analysis of the evolution of the slope boundary due to erosion by rainfall and the softening effect of the soil-rock media by infiltrated water, we conclude the main reason of the occurrence of this landslide is that the foot of the slope had been continuously eroded by the water-flow down from the up-reach during rainfall. The existence of the deep gully also provided well geological condition for continuing sliding. Though there is no life loss in the event, the distance between the resident house and west boundary of the slope is less than 10 m, and some houses have been damaged with long cracks. Measures should be taken on the slope after slide to prevent larger hazard from happening, especially for the security of the local residents. A primary plan has been presented in this paper. It should note that these measures are identical with the scheme for treatment of whole Baiyi'an landslide group, which has been proposed in existed literature.