泸定县四湾村滑坡的地质成因与稳定评价

GEOLOGICAL ORIGIN AND STABILITY EVALUATION OF SIWANCUN LANDSLIDE IN LUDING COUNTY

四湾村古滑坡体位于在建的大渡河泸定水电站下游约1 km处,其稳定性对电站的设计、建设和运营均存在较大影响。为评价滑坡的稳定性,对其进行详细的地质勘察和测试分析工作,并在此基础上分析其形成与演变过程,建立地质结构模型。该滑坡为一由地震诱发形成的高速滑坡,ESR法测年揭示其形成年代为17.2±2 ka B.P.,即晚更新世晚期。滑坡曾堵塞大渡河,滑坡坝溃决后滑坡堆积体发生过3次次级滑移。残留的滑坡堆积体呈帚形,长约700 m,宽约800 m,最大厚度137.62 m,体积约5.0×107 m3。堆积体前缘延伸至大渡河河床,临河为40°的陡坎,中后缘整体平缓。物质成分为花岗岩和闪长岩块石,夹块碎石土,透水性良好。勘察期间没有发现滑坡存在有宏观变形迹象。采用三维强度折减法和极限平衡法对滑坡的稳定性进行评价,安全系数分别为1.49和1.42。滑坡稳定性良好。

Siwancun landslide locates at 1 km downstream of the dam site of Luding Hydropower Station and its stability has great influence on the dam design, construction and operation. In order to evaluate its stability, detailed geological investigation and tests are carried out; geological origin and evolution are analyzed, and a geological structural model is established. The landslide is a high-speed one induced by earthquake dated back to 17.2+2 ka B. R, i.e. the late period of Late Pleistocene by ESR method. The landslide dammed Dadu River experienced at least 3 secondary slides after dam break. The present landslide fills is of broom-shaped, around 700 meters long, 800 meters wide and the maximum depths of 137.62 m. The total volume is about 5.0 × 107 m3. Its toe extends into the bed of Dadu River. At its front, the bank slope is steep with a slope of 40°, while the middle and rear parts of the slope are gentle. The slide fills are mainly composed of boulders and granular soils of granite and diorite origin, with good permeability. No deformation is evidenced during site investigation. Three-dimensional stability evaluation is carried out using the strength reduction technique and limit equilibrium method; and the factors of safety are 1.49 and 1.42, respectively. It is shown that the landslide is stable.