三峡库区靠椅状土质滑坡变形规律及机理--以秭归八字门滑坡为例

Study on the deformation law and mechanism of chair-shaped soil landslide in Three Gorges Reservoir area--Taking the landslide of Baguamen in Zigui as an example

三峡水库蓄水以来,不少滑坡监测位移-时间曲线呈阶跃变化,导致稳定状态识别难度较大,严重影响滑坡预警预报,靠椅状土质滑坡尤为明显。以八字门滑坡为例,通过多次野外地质调查、长期现场巡查、10多年的GPS位移监测数据、2年多全自动监测数据等,较深入研究了该滑坡在库水涨落及降雨条件下的变形规律。结果表明,库水位下降期间,特别是库水位下降15m以后,由160m下降至145m,滑坡体变形存在20d左右的滞后,滑坡变形曲线出现突跃,日位移量达1.5~2.2mm。一次降雨量在80mm以上会明显诱发坡体加速。库水位上升期间,库水位在175m左右时,月位移量出现5~10mm负值。一次降雨量在150mm左右未能诱发坡体加速;但一次降雨量在200mm以上,滑坡体位移速度明显加大。滑坡体在降雨量诱发后,位移加速后在降雨结束后持续5~7d恢复正常水平。在周期性降雨和库水位涨落的循环作用下,滑坡体反复受到"推-拉"作用,导致滑坡的位移-时间曲线呈阶跃特征。靠椅状土质滑坡为一类特殊的滑坡,库水位升降是八字门滑坡目前变形的主要因素,而降雨对滑坡变形起到了促进作用。受靠椅状等坡体结构特征制约,在库水位升降作用下坡体会反复变形,但难以发生快速的整体破坏。

Since the impoundment of the Three Gorges Reservoir,the displacement-time curve of many landslides has shown a step change,which makes it difficult to identify the steady state and seriously affects the landslide early warning and prediction.The chair-shaped soil landslide is particularly obvious.Taking the Bazimen landslide as an example,this paper studied the landslide in the reservoir water through multiple field geological surveys,long-term on-site inspections,GPS displacement monitoring data obtained for more than 10 years and additional 2 years of fully automatic monitoring data.Deformation law under fluctuations and rainfall conditions were studied in depth.The results showed that during the decline of reservoir water level,especially after the water level dropped by 15 m,it decreased from 160 mto 145 m,and the landslide body deformation would have a lag of about 20 d.The landslide deformation curve suddenly jumped and the daily displacement reached 1.5 mm to 2.2 mm.When the rainfall occurred more than 80 mm it obviously induced the acceleration of the slope.During the escalation of the reservoir water level,the reservoir water level was around 175 mand the monthly displacement have a negative value of 5 to 10 mm.When rainfall was about 100 mm,it failed to induce the acceleration of the slope.But once the rainfall was above 200 mm,the displacement speed of the landslide body increased significantly.After the rainfall was induced,the landslide body accelerated to a normal level after 5-7 days of rain.Under the cyclical action of periodic rainfall and reservoir water level fluctuation,the landslide body was repeatedly subjected to the "push-pull" effect,resulting in the step-time curve of the landslide′s displacement-time curve.The chair-like soil landslide was a special type of landslide.The increased and decrease of the reservoir water level was the main factor of the current deformation of the Bazimen landslide,and the rainfall has promoted the deformation of the landslide.Restricted by the structural characteristics of the chair and other slopes,the slope would be repeatedly deformed under the elevation of the reservoir water level,but it was difficult to cause rapid overall damage.