2012年6·29贵州岑巩龙家坡滑坡灾害的基本特征与成因机理一个由侧向剪切扰动诱发大型滑坡的典型案例

摘要

侧向剪切扰动诱发滑坡是一种新型滑坡类型，深入研究其成因机理，有助于开展滑坡预警工作。2012年6月29日6时20分左右，贵州省岑巩县思旸镇龙家坡山体发生大规模滑坡，300～400万 m3岩土体失稳后堵塞坡下的马坡河，形成20余 m高的堰塞坝及库容达7万余 m3的堰塞湖。笔者在对灾害现场进行详细地质调查的基础上，结合现场调绘、航拍、颗分试验等手段，对龙家坡滑坡的基本特征进行了分析研究，对滑坡发生及成灾原因进行了初步分析。结果表明：滑坡区风化破碎的厚层堆积体、有利的岩层倾向以及前缘临空是滑坡发生的基本条件；滑坡区南侧地下水径排区被堆填大量粉黏土弃渣，不仅为该区斜坡人为增加了巨大推力，还使该区斜坡地下水局部富集。在强降雨条件下，南侧堆积区首先发生滑动，其对主滑体的侧向剪切扰动作用带动主滑区大规模失稳破坏。由此，对这类侧向剪切扰动诱发的滑坡，在进行地质灾害调查和预警时，除了应调查其岩土体特征外，还必须查明其边界条件。%As a new landslide type,its genetic mechanism of landslide is triggered by lateral shear disturbance.The large scale landslide occurred at Longjiapo,Cengong in Guizhou Province on June 29, 2012.The landslide,with its volume ranging from 300×104 to 400×104 m3 ,became a 20 m weir dam in height blocking up the Mapo River in the lower part and a dammed-lake with about 7×104 m3 in volume. Based on site investigation,the authors provide detailed characteristics of the landslide and analyze the mechanism of the landslide.It is combined with in-situ grain size composition experimentation,aerial photography and other means.The results indicate that,there were weathered thick accumulation body in the landslide area,and that inclination direction of rock stratum and terrain condition of slope were the favorable fundamental conditions to the landslide.The south part of slide areas,which was a natural guiding gutter of groundwater,had been filled in large amounts of silty clay.In that case,it exerted a large additive gravity force on the ground,and it also induced local groundwater enrichment in the slope body.After the rainfall,part of water seeped into the soil mass and reduced the shearing strength of soils.Then,the slope body in the south area slid firstly,and the motion took great lateral shear perturbation to the main slide area.The main slide area was driven to slide.It deserves intensive study as it is pretty special that the lateral shear disturbance triggered a large landslide.Hence,in addition to its characteristics of rock and soil in the landslide,the geo-conditions of both sides must be investigated in disaster early warning and mitigation.