丹巴县莫洛村滑坡的地质成因与稳定评价

Geological cause and stability evaluation of Moluocun landslide, Danba county

莫洛村滑坡位于大渡河左岸猴子岩水库库尾的梭坡堆积体前缘,是丹巴县古碉的集中分布区之一。由于古碉群独特的历史、人文和旅游价值,其稳定性不论是对古碉群保护,还是对水库蓄水位选择均十分重要。在简介滑坡区域地质环境的基础上,基于地质勘察和现场调查资料,分析了堆积体与滑坡地质成因与稳定现状,同时采用三维强度折减法和二维极限平衡法预测了不同蓄水位与水库运行方案对其稳定性的影响。结果表明:梭坡堆积体是冰川作用形成的;莫洛村滑坡是堆积体前缘近3 300年来蠕变和局部解体形成的,总方量约为4 000×104m3;导致滑坡变形的原因是1983年后向坡体引水,坡体地下水位抬升;现状下滑坡的二维极限平衡法和三维强度折减法安全系数分别为1.048和1.07,处于临界稳定状态;不论是1 842m还是1 852 m水位方案,水库蓄水与运行对滑坡稳定的影响均很小;排水是维持滑坡稳定和保护古碉的最有效措施。

Moluocun landslide lies on the left bank of the Dadu river and at the tail of Houziyan reservoir.It is at the toe of Suopo deposit,on which the renowned Danba watchtowers concentrate.Due to their unique historical,cultural and sightseeing values,the stability of the landslide is important both to the preservation of the towers and to the selection of rational reservoir level.After introduction to local geoenvironmental conditions,the formation and stability of both Suopo deposit and Moluocun landslide are analyzed based on site investigation and field reconnaissance,numerical evaluation is also made to the stability of the landslide under different reservoir levels and operation schemes by three dimensional strength reduction technique and two dimensional limit equilibrium method.Results show that： Suopo deposit is the result of glaciations.Moluocun landslide is formed due to the long-term creep and disintegration of the toe of Suopo deposit in the past 3 300 years and its total volume is around 40×106 m3.The two diversion ditches constructed after year 1983 raised the water level in the landslide,worsened its stability and made its head and toe crack successively.Under present state,the landslide is in critical state and its safety factor is 1.048 and 1.070 obtained by using 2D limit equilibrium method and 3D strength reduction method respectively.Whether the reservoir level is 1 842 m or 1 852 m,the influence of reservoir impounding and operation on landslide stability is quite small.Drainage is the most efficient measure to maintain the landslide stability and to preserve the watchtowers.