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

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 15 m 以后, 由 160 m 下降至 145 m, 滑坡体变形存在 20 d 左右的滞后, 滑坡变形 曲线出现突跃, 日位移量达 11 5~ 21 2 mm。一次降雨量在 80 mm 以上会明显诱发坡体加速。库水位上升期间, 库 水位在 175 m 左右时, 月位移量出现 5~ 10 mm 负值。一次降雨量在 150 mm 左右未能诱发坡体加速; 但一次降雨量 在 200 mm 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~ 7 d 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0 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 t he im poundment o f the T hree Gorg es Reserv oir, the displacement2t ime curve of many landslides has shown a step chang e, w hich makes it difficult to identify the steady state and seriously affects the landslide early w arning and prediction. The chair2sha ped so il landslide is particularly o bv ious. T aking the Bazimen landslide as an ex ample, this paper studied the land2 slide in the r eser voir w ater throug h multiple field geo log ical sur vey s, long2term o n2sit e inspectio ns, GPS displacement monito2 ring data o bt ained for mo re than 10 years and additional 2 y ea rs o f fully automat ic mo nitoring data. Defo rmatio n law under fluc2 tuatio ns and rainfall conditions wer e studied in depth. The results showed that during the decline of r eser voir w ater lev el, espe2 cially after the w ater level dro pped by 15 m, it decr eased fr om 160 m to 145 m, and the landslide bo dy deformat ion would have a lag of about 20 d. T he landslide defo rmation curve suddenly jumped and the daily displacement reached 11 5 mm to 21 2 mm. When the rainfall occurr ed mor e than 80 mm it o bv io usly induced the acceler atio n o f the slo pe. During the escalation of the res2 er voir w ater level, the reserv oir water lev el was ar ound 175 m and t he monthly displacement hav e a neg ative value of 5 to 10 mm. When rainfall w as abo ut 100 mm, it failed to induce the acceler at ion of the slope. But o nce the r ainfall was abo ve 200 mm, the displacement speed of the landslide body increased significantly. After the rainfall was induced, the landslide body acceler2 ated t o a normal level after 527 day s of rain. Under the cyclical action of periodic rainfall and r eser vo ir water level fluctuatio n, the landslide body w as repeatedly subjected to the " push2pull" effect, resulting in the step2time curv e o f the landslidec s displace2 ment2time curv e. The chair2 like soil landslide w as a special type of landslide. The increased and decrease of the r eser vo