三峡库区树坪滑坡受库水位变化产生的变形特征

中国三峡工程是当今世界上最大的水利水电工程。在2003年6月第一次蓄水至高程135m以后,发生了大量的滑坡复活及失稳现象。树坪滑坡是变形较为严重的滑坡之一。树坪滑坡属于发生在三叠系巴东组砂岩及页岩中的大型古滑坡。三峡库区的初次蓄水引起了树坪滑坡的复活,并对坡体居民的生活和长江航道的安全构成极大威胁。在GPS观测、坡体裂缝观测以及伸缩计观测数据的基础上,对库水位变化所引起的树坪滑坡的变形特征进行了分析。同时,为了解滑坡范围内地下水的分布特征,进行1m深地温测试,并对地下水存在状况进行推测。变形观测结果表明,在古滑坡的头部没有明显变形。在滑坡体上部,变形以拉伸为主,在滑坡体下部,变形以压缩为主;在滑坡体中部,没有明显的压缩和拉伸。与水库蓄水同步开始的GPS观测结果表明,蓄水开始时,滑坡体下部的变形速率较上部快,而在2005年6月,滑坡体下部的变形基本结束,滑坡变形主要体现为上部滑坡的向下滑落并挤压下部滑坡体。根据地下水的探测结果以及对滑坡变形与降雨量之间的比较,可以推测树坪滑坡的变形不仅受到库水位变化的影响,同时也受到地下水的影响。

DEFORMATION FEATURES OF SHUPING LANDSLIDE CAUSED BY WATER LEVEL CHANGES IN THREE GORGES RESERVOIR AREA, CHINA

The Three Gorges dam construction on the Yangtze River in China is the largest hydroelectric project in the world.After the first impoundment in June 2003,many landslides occurred or were reactivated.Shuping landslide is one of the most active landslides among them,which is a reactivated landslide occurred in shale and sandstone of Tertiary period.As soon as the first impoundment of the Three Gorges reservoir was conducted,serious deformation occurred in the Shuping landslide.It formed a large dangerous factor for the local residents and the shipment in the main stream of the Yangtze River.The deformation of the Shuping landslide is monitored by GPS extensometers;and crack measurements are summarized.Based on the monitored data,the deformation features of the Shuping landslide caused by water level changes are analyzed.Also,for the investigation of the groundwater situation,1 m-depth ground temperature measurement was conducted;and the groundwater veins were estimated.It is found that there was no obvious deformation occurred in the head of the landslide.Extension deformation occurred in the upper part,and comparison deformation occurred in the lower part,while the deformation at the middle part was not obvious.As indicated in GPS monitoring results sooner after the impoundment of the reservoir,the lower part has faster displacement rate downward faster than that of the upper part.Currently,the displacement of the lower part was almost terminated while the upper part displaced downward gradually and compressed the lower part at the current water level.Through the investigation on the groundwater and comparison of deformation with rainfall data,it is estimated that the water level change of the Yangtze River is not the only affecting factor for the reactivation of the Shuping landslide.Groundwater condition of the Shuping landslide should also be further investigated.