中国西部地区典型岩质滑坡机理研究

中国西部具有独特的地域地质环境和活跃的内外动力地质条件。在这样的背景下,崩滑地质灾害十分发育,给人类居住环境及重大工程建设带来极大威胁和重大的损失。阐明这些灾害的形成机理,尤其是大型滑坡的发生机理,对灾害的防治具有重要的理论及现实意义。根据作者在中国西部地区多年的研究工作实践,对几类典型的大型岩质斜坡变形及失稳机理进行了较为深入的分析,重点阐述了这些大型滑坡形成的地质条件、斜坡变形过程及发生机理 的"概念模型",其中包括滑移-拉裂-剪断的三段式模式、挡墙溃决模式、"超级强夯"模式等。这些机理及模式的提出,对这一地区的防灾减灾实践具有一定的指导意义。

MECHANISM OF LARGE SCALE LANDSLIDES IN WESTERN CHINA

China is a big country with various topography types and geological structures, especiallyin its southwestern part, the interior and epigeneticgeological process are very active because of the special location of the margin area of Tibet Plateau. The intensive uplift of the Plateau since the Quarterly time resulted in a distinctive topographical contrast with the plateau and lower basins, high mountains and deep valleys. Moreover, the extension of the Plateau towards the east and southeast resulted from the collision between Indian plate and Europe Asian one brings about the appearanceof large active faults around the Plateau and strong earthquakes. All of these lay a strong geoenvironmental backgrounds for the occurrence of large scale landslides in this area. 
A lot of evidences show that a new increase period of landslides has comes in China since 1990s,especially some typical hazardous landslides occurred in this period. Even though this kind of increase has been thought to be related to the large scale infrastructures construction, it is a common sense that the fundamental geologic mechanics model should be involved in the sliding process. Therefore, it is very significant to discuss the mechanism of these landslides and summery some typical models. The author's work reveals following typical huge landslides mechanism.
(1) Creep tension shearing fracture model (three segments mechanism): This kind of mechanism occurs in the slope contained nearly horizontal or gently out inclined soft layers or weak planes. The slope deformation and failure is controlledby the weak plane generally located at the base of the slope. With the unloading process of the slope from river down erosion or slope cutting, the creep deformation occurs along the weak plane and a tension crack will appear at the top of the slope. The continuous creep deformation will promote the gradually deepening of the tension crack and a locked segment will appear at the middle part of the potential slip surface. Obviously, stress will be concentrated at the locked section and this section will be formed to be a key part controlling the slope stability. When the concentrated stress reaches to a criticalextent, the locked section will be cut through with a sudden brittle shearing failure, and a hazardous landslide occurs.
(2) “Retailing wall” collapsemodel: it is generally involved in the slope with a soft base and a rigid section above it. The later one can be regarded as a "locked section" on theslip surface and it acted as a “retailingwall”because it supports the driving force from the upper slope. Obviously, the stress will be accumulated gradually in the “retailing wall”with the increasingof the driving force from the upper slope and the continuous squeezing out deformation of its soft base. Finally, the “retailing wall” located at the middle part of the slope will be destroyed due to exceed stress accumulation, and the slip surface will be formed.
(3) “Super punching”mechanism model: it describes the process that a unstable block slides down from a sharply steep slope or mountain and it impacts very strongly on a debris at the slope foot, and induces the debris integrating suddenly and flowing a long distance in a moment time. Generally, the unstable block has very huge potential energy for its high position and its instabilitycomes very suddenly. The induced debris flow moves very quickly and has almost all the characters of high speed mass flows such as high velocity, long travelingdistance, lower apparent friction angle, special moving trajectory, air cushion effect traces, even forming a lake as it reaches a river. In most cases this kind of model means a big hazard and beyond recall losses. 