金沙江白格滑坡裂缝区失稳概率分析

Instability Probability Analysis of the Cracking Zones at the Site of the Baige Landslide in Jinsha River

金沙江上游白格滑坡于2018年10月10日和11月3日连续发生两次滑坡堵江–溃坝事件,给沿岸居民带来巨大灾害。滑坡发生之后,在滑坡体后缘形成3个裂缝区,存在再次滑坡堵江的可能。鉴于白格滑坡岩土体试验数量有限,试验成果难以反映坡体抗剪强度参数的统计特征,本文针对白格“11·3”滑坡,采用基于极大似然估计的优化算法,对滑坡岩土体的抗剪强度参数进行了反演;并利用反演参数,采用蒙特卡洛方法对滑坡后缘裂缝区进行了可靠度计算和稳定性评价。研究表明:1)将响应面法与基于极大似然的概率反分析方法结合起来对滑坡体参数进行反演,计算过程简便,计算方法适应性强。2)根据白格“11·3”滑坡反演得到的滑坡岩土体抗剪强度黏聚力后验分布为N(13.05 kPa,32),内摩擦角后验分布为N(0.64,0.042),计算结果表明通过反演可以降低先验参数的不确定性。3)采用自动搜索最危险滑动面方法得到各裂缝区的局部破坏模式。计算得到的最危险滑动区范围与现场调查及监测得到的失稳区范围基本一致,且局部破坏模式下的破坏概率均明显大于整体破坏模式,表明裂缝区破坏以渐进牵引破坏为主,与实际的裂缝发展规律及破坏模式一致。4)白格滑坡后缘3个裂缝区的潜在失稳区域C1–1、C2–1和C3–1的体积分别为7×105 m3、3.2×106 m3和1.3×106 m3,对应的失稳概率分别为21.70%、33.90%和27.30%,均为极高危险性。因此,有必要对滑坡堵江–溃坝洪水灾害链进行风险评价,并提出合理的处置措施和应急预案。

Baige landslide,which located on the upper reaches of Jinsha River,happened successively on October 10 and November 3,2018 and blocked the river twice.The dammed lakes and their breaching flood brought about severe disaster to local residents along the river.After the sliding,three cracking zones were formed at the back edge of the landslide,which may block the river again.In view of the uncertainty of the physical and mechanical parameters of the landslide,the optimization algorithm was utilized based on the maximum likelihood estimation to inverse the shear strength parameters of the landslide,and the inversion parameters were used to calculate the reliability and evaluate the stability of the cracking zones by Monte Carlo method.The results showed that:1)Combining the response surface method with the maximum likelihood based probability back analysis method,the calculation process was simple and the calculation method had a strong adaptability.2)According to the inversion results of Baige“11·3”landslide,the posterior distribution of shear strength cohesion and internal friction angle were N(13.05 kPa,32)and N(0.64,0.042),respectively.The uncertainty of prior parameters could be reduced by inversion.3)The local failure mode of each cracking zone was obtained by searching the most dangerous sliding surface.The calculated scope of the most dangerous sliding area of each cracking zone was approximately the same as that of the instability area obtained from the field investigation and monitoring,and the failure probability under the local failure mode was significantly greater than that under the overall failure mode,indicating that the failure of the cracking zone was mainly progressive traction failure.4)The volumes of the cracking zones C1–1,C2–1 and C3–1 at the back edge of Baige landslide were 7×105 m3,3.2×106 m3 and 1.3×106 m3,respectively,with the corresponding instability probability of 21.70%,33.90%and 27.30%,all of which were extremely dangerous.It is necessary to carry out risk assessment on the damming-breaching-flooding disaster chain,and put forward appropriate disposal measures and emergency plans.