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。

Study on the deformation law and mechanism of chair2shaped soil landslide in Three Gorges Reservoir area --Taking the landslide of Baguamen in Zigui as an example

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 ir w ater level was the main factor of the current defo rmatio n of the Bazimen landslide, and the rainfall has promo ted the deformat ion of the landslide. Rest ricted by the st ruct ur al characteristics of the chair and other slo pes, the slope w ould be repeatedly defo rmed under the elevation of the reserv oir wat er lev el, but it w as difficult to cause rapid over all damag e.