水库环境中结构复杂大型滑坡内地下水的力学作用规律与滑坡复活模式研究

It has long been recognized that occurrence and activity of most landslides in the world are closely related to mechanical roles of groundwater within landslides. However, mechanical roles of groundwater within landslides can not be properly quantified when the landslides' structure are complex due to groundwater's complicated occurence and runoff, which has been thought to be one of the most chalenging issues in the field of landslide research. Reservoir is one of artifical environments which leads to significant change of groundwater regime within its bank slopes. Consequently, many landslides occur there. Of them, most are reactivated old landslides due to their loose materials and exiting weak zones (slip zones). However, kinematic patterns of these landslide vary greatly. Three Gorge reservoir area is one area where old landslides are the most widely distrubted in China and many of them have been reactived since operation of the reservoir. To investigate mechanical roles of groundwater within the reservoir-induced large landslides with complex structures and their relationship with landslides' kinematic patterns, this proposal attempt to focus on reactived landslides with complex structures in the Three Gorge area. Mechanical role of groundwater within the landslides and kinematic patterns as well as their relations will be explored by ananlysing mornitoring data of the landslides and physical model tests and numerical simulation based on typical prototype landslides in the area. It iis expected that groundwater's mechanical role of within the landslides can be quantified based on variation of seepage filed following reservoir fluctuation, and that kinematic pattern of lanslides' reactivation can be generalized according to variation of stress field and displacement field upon changes of the seepage field.

地下水力学作用是滑坡形成与活动的主要原因之一。然而结构复杂滑坡中地下水的赋存、径流方式纷繁，造成地下水在滑坡中的力学作用类型及其作用强度变化多样。结构复杂滑坡内地下水力学作用规律是滑坡研究中最有挑战性的科学问题之一。水库是对滑坡地下水动态改变最大的外部环境，大型老滑坡是自然界中结构最复杂的滑坡。老滑坡复活是对水库威胁最大的斜坡失稳类型。本项申请拟以三峡库区复活老滑坡为研究对象，在对该地区复杂大型滑坡结构类型划分和水文地质概化模型研究基础上，基于典型的滑坡多年监测数据，分析大型老滑坡复活模式；通过一系列物理模型试验、数值模拟，探索库水位波动条件下，各类复杂滑坡中地下水渗流场变化规律及其主控因素，研究滑坡应力场、位移场随渗流场变化规律，进而探寻地下水在不同类型结构复杂滑坡中的力学作用类型及其作用强度以及各类滑坡复活模式。

由于其先天存在的软弱结构面和破碎滑体结构，滑坡复活是库水位波动引发的最常见滑坡形式。滑坡复活的本质是库水位导致滑坡内地下水渗流场改变造成的孔隙水压力变化。老滑坡内地下水渗流场变化受滑坡结构控制。本项研究以三峡库区秭归-万州段大型老滑坡为主要研究对象，在系统研究60个大型老滑坡发育特征和地下水动态及其与库水位波动关系后发现，三峡库区分布三大类、七个亚类不同结构滑坡。不同结构类型滑坡复活模式及其强度不同，滑坡复活模式受滑坡结构和滑体渗透性差异控制。基于大型物理模型试验研究发现，随着库水位波动和不同结构滑坡滑体渗透性的差异，滑坡内地下水的力学作用表现为不同方式的孔隙水压力，孔隙水压力的作用方式表现为滑体内浮托力、滑带底部扬压力和滑体内渗透压力；不同类型地下水力学作用强度受滑体渗透性控制。不同渗透性滑体内孔隙水压力变化幅度与滑体渗透性负相关，与库水位升降速度正相关；分层变形模式，波动式累进性发展，变形速率与滑体渗透性负相关、库水位波动速率正相关。渗透性最小滑体变形最大，反之变形最小，滑坡变形伴随库水位升降的波动式累进性发展。对不同结构滑坡的数值模拟研究结果与物理模拟试验结果基本一致。复活滑坡中，水库蓄水很短时间内滑坡复活不仅与地下水升高造成的力学作用有关，还与滑带残余强度衰减有关；反之，水库蓄水较长时间后，滑坡复活仅与随库水位升降变化的地下水力学作用直接相关。