摘 要 大光包滑坡是汶川地震触发的规模最大的巨型滑坡。滑坡位于安县高川乡、汶川地震发震断裂上盘，滑动距离4.5 km，堆积体宽度2.2km，面积7.8 km2，估算体积7.5亿m3。与地震灾区178处特大滑坡相比，大光包滑坡除了强震触发崩滑灾害具有的震动溃裂、溃滑失稳、超强动力和大规模高速抛射与远程运动等特征之外，其存在一个长度大于1km的长大滑面，是其余滑坡绝无仅有的！作者在去年研究的基础上，又多次到现场调查、测绘并取样分析，初步认为大光包滑坡发生过程为一次性完成，滑带物质组成较为复杂，主体为震旦系（Zd）风化程度较高的泥质灰岩，局部夹泥盆系沙窝子组（Ds）磷矿及其伴生矿。滑坡形成机理主要分为以下3个阶段：即(1)坡体震裂阶段：在强震作用下后缘拉裂边界及上游拉裂边界形成，并与下游侧的岩层层面构成巨大的V型楔形体；(2)滑面碎裂化，摩阻力急剧降低阶段：滑坡下游边界（主控滑动面）滑床被震裂、松弛、剪胀-扩容并碎裂化，产生滚动摩擦效应，导致滑面摩阻力急剧降低；(3) 前部锁固段剪断，高速溃滑阶段：滑体前部滑面上的锁固段在强震持续作用下，产生突发性剪断，从而导致整个巨大的楔形体，如同拉抽屉一样，沿岩层走向高速溃滑而下；（4）震动堆积阶段，滑体冲过黄洞子沟，受到迎面山体的强力阻挡，逆冲爬高500余m后，表部惯性极大的松散岩土体快速折返并震动堆积、荡平，余势不减的碎屑流汇入滑坡扩容抛撒体，向黄洞子沟下游流动1km，止于大偏桥。
Abstract Daguangbao landslide in Anxian county Gaochuan town is located on the upper plate of the Causative Fault of wenchuan earthquake. Its slide distance is 4.5 km, and its maximum width of accumulation is 2.2 km. The area is 7.8 km2, and estimated volume is 750 million m3. It is the largest landslide among individual landslides triggered by Wenchuan earthquake. Comparing with the other 178 large landslides in earthquake disaster area, Daguangbao landslide has the same characteristics as falls and slide disaster triggered by strong earthquake. They include shake debacle, unstability of debacle and slide mechanism, super-dynamic characteristics, large-scale and high-speed projectile, and long-distance movement．But it has itself standout trait, namely, a long-large sliding surface more than 1 km long and 100～250 m wide, which is in a class by itself. On the basis of the study last year, the author has further progressed the site investigation many times, and has finished mapping and sampling analysis. The preliminary view is that Daguangbao landslide occurring process is one-time completion. Composition of sliding zone is very complex. It is mainly composed of stronger weathering argillaceous limestone of Sinian, and its part stratum contains Devonian shawozi sub-group (Ds) and its associated phosphate ore. Its formation mechanism can be divided into the following 3 stages. (1) Stage of slope shattering cracking. Rear fracturing boundary and upstream fracturing boundary were shaped under strong earthquake, and they composed huge wedge Vwith downstream rock beddings. (2) Stage of friction decrease and slope shattering-sliding. Sliding bed at downstream boundary (the main controlling sliding surface) began shattering-cracking, relaxation, cutting expand-bulk enlarge. Strolling scrape effect made the friction decrease sharply, and made the huge wedge slide with high speed along bedding strike, like pulling drawer. (3) Stage of shattering-slidingshaking- accumulating. Landslide body rushed into Hongdongzi gully and was barred strongly by faced mountain，so it thrust up more than 500 m，and then its surficial loose accumulation with large inertia began fastly backing and shaking, accumulating, shaking level. Debris flows whose inertia force did not decrease imported landslide and enlarged ejection body. At last, it stopped at Dapianqiao bridge after flowing 1 km towards downstream of Hongdongzi gully.
Key words Daguangbao landslide, character of landslide, model of geomechanics, formation mechanism,
shattering expand and surper press