高寒高海拔山区节理化花岗岩高速远程滑坡启滑机制研究――以理塘乱石包滑坡为例

Mountains made up of granite are commonly regarded as geological bodies with high stability, but the jointed fissures induced by tectonics often make the granite become structural plane developed rock mass. However, in recent years, several large/giant-scale and long-runout landslides associated with jointed granite rock have occurred or been found along active faults and with no earthquakes happened, on the high altitude and alpine mountain area, the eastern part of the Tibetan Plateau. This problem severely restricts the planning and construction of major infrastructure projects, such as the Sichuan-Tibet railway. In this project, the particularity of mechanical properties of the jointed granite rock mass in active tectonic regions with extreme cold weather and at high-altitudes will be analyzed. Field studies will be conducted to investigate the effect of varying conditions on the properties of granite. In particular, changes in microstructure, macro-mechanical properties along with weakening mechanisms under freeze-thaw and other extreme climate conditions. In addition, we will use the conventional and unconventional rock mechanical testing, coupled with numerical simulations, etc., in order to understand the failure mechanisms of jointed granite under extreme conditions. The giant long-runout landslide is examined here as a case study, which took place in granite rock, in Litang County. The inversion of the formation process will be simulated for the landslide. The numerical model is based on tectonic background analysis, structure analysis and mechanical testing of jointed granite rock mass. In addition, spatial development characteristics and evolvement rule of landslide detritus are taken into account. Key factors that trigger landslides are investigated in this study. Formation condition, starting mechanism and kinematical characteristics of landslides coupled with effects of temperature, force and ice/water will be analyzed. A detailed analysis of present stability conditions, development trends, and instability criterion for landslides in riprap areas will be discussed. This study has important theoretical and practical significance to facilitate understanding and enable early identification of the landslide activation mechanisms for long-runout landslides of jointed granite in extreme cold weather conditions at high-altitude.

花岗岩通常被认为是稳定性较好的地质体，但构造作用产生的节理裂隙常使其成为结构面发育的节理化岩体。近年来，在青藏高原东部高寒高海拔山区，在断裂带附近、在未发震的情况下发现很多与节理化花岗岩有关的高速远程滑坡，严重制约着川藏铁路等重大工程规划建设。本项目拟抓住高寒高海拔活动构造区节理化花岗岩力学性质的特殊性，采用野外调查、常规和非常规岩石力学测试、数值模拟等手段，剖析节理化花岗岩的岩体结构特征、宏微观力学性质及冻融作用下的弱化机理。以理塘乱石包高速远程滑坡为例，基于节理化花岗岩的构造背景分析、岩体结构分析、不同状态下的力学性质测试、滑坡碎裂物质空间分布与演变规律分析等，反演乱石包滑坡的形成过程，深入研究温度－力－冰水三场耦合作用下滑坡的启滑机制和运动学特征；对乱石包滑坡的现今稳定性和发展趋势进行分析，探讨其失稳判据。本项研究对认识节理化花岗岩类高速远程滑坡的启滑机制和早期识别具有重要指导意义。

以青藏高原东部发育的高速远程滑坡为研究对象，在典型高速远程滑坡野外调查、试验测试和数值模拟分析的基础上，取得如下主要成果：.（1）川西理塘乱石包高速远程滑坡位于川西理塘毛垭坝盆地东北侧，滑坡的滑动方向垂直于理塘－德巫断裂的北西段，约形成于1980±30a BP左右，最大滑行距离达3.83km，滑坡后壁与前缘堆积区的高差约820m，方量约0.64~0.94×108m3，滑动速度可达53.25m/s。.（2）乱石包滑坡一带古地形较为平缓，仅为25~26°，有限元模拟结果表明，仅在重力和降雨作用下，乱石包古斜坡发生失稳滑动的概率小，研究认为：① 理塘－德巫断裂全新世以来活动强烈，具有强震地质背景，由断裂活动诱发强震应是乱石包滑坡形成的主要因素；② 距今2000a BP左右，青藏高原温度变化较大，该时期发生的大规模冰川可能是诱发乱石包滑坡发生的因素之一。.（3）新发现西藏加查拉岗村高速远程滑坡、日阿莫巨型崩塌等地质灾害，研究认为背斜构造对拉岗村高速远程滑坡具有重要的控制作用，背斜的翼部造成的斜坡应力场与一般岩体斜坡具有较大差异，往往容易形成高速远程滑坡。.（4）冻融岩石力学和微观结构测试分析认为花岗岩内部损伤程度随着冻融次数的增加而增加，单岩石波速则随着冻融次数的增加而明显降低；从核磁共振T2弛豫时间规律认为风化较严重的岩样经过冻融循环后裂隙尺寸进一步增大，而风化程度微小的岩石经过冻融后裂隙尺寸范围较为集中。岩石的单轴抗压强度和弹性模量随冻融次数增大而减小，而泊松比和内摩擦角没有表现出明显变化规律。基于试验数据和理论分析，提出了冻融损伤本构模型，可对不同围压和冻融循环次数条件下的岩石应力应变全过程进行模拟和预测。.（5）通过对比国内外典型高速远程滑坡的数据，建立了高速远程滑坡的体积、活动距离相关性公式，L=12.52V0.37，对滑坡风险管理和防灾减灾具有一定指导意义。.（6）结合研究成果和重大工程规划建设，提出了川藏铁路毛垭坝盆地段、西藏加查段线路优化建议，并应用于四川茂县6•24特大滑坡灾害应急调查中。