水库老滑坡间歇性复活机制与地表位移预测模型研究

The intermittent reactivation of reservoir ancient landslides brings great difficulties to decision managers who should judge the landslide which deformation phase be and what the future development trend will be. In order to reveal the mechanism of intermittent reactivation and develop an applicable model for predicting ground displacement, 60 reactivated landslides in the Three Gorges Reservoir will be selected as the study cases. The kinetic equations which describe the intermittent reactivation will be proposed based on statistical analysis and theoretical derivation. On this basis, the tests which cover three aspects, i.e. shear rate effects on residual shear strength, peak shear strength recovery with different consolidation duration and pore-water pressure diffusion, will be performed on the soil specimens from the sliding zone. The above three groups of tests correspond to sliding, sliding dormancy and excitation of sliding dormancy to sliding, respectively. Landslide boundary conditions like fluctuation of reservoir water level and precipitation will be united to the variation of groundwater level. The delayed response of landslide reactivation caused by variation of groundwater level to landslide boundary conditions will be investigated, and the empirical equation that describes the delayed response will be obtained. The displacement prediction model can be proposed based on the delayed equation and kinematical equation above with the predicted series of groundwater level. The results will have important scientific significance on revealing the intermittent reactivation of reservoir ancient landslides and improving the displacement prediction model, as well as formulating the plans of disaster prevention and mitigation.

水库老滑坡的间歇性复活给决策管理者判断滑坡处于何种变形阶段，以及未来将会出现何种发展趋势带来了极大的困难。为揭示此复活机制并建立适用的地表位移预测模型，本项目拟以三峡库区60个处于复活期的老滑坡为研究对象，基于统计分析和理论推导建立描述这一间歇性复活过程的动力学方程。在此基础上开展滑带土残余强度剪切速率效应试验、不同固结时长下的峰值强度恢复试验及孔隙水压力扩散试验。试验分别对应水库老滑坡间歇性复活过程中的滑动期、间歇期以及由间歇期进入滑动期的激发过程。将滑坡边界上库水位变动与降雨入渗统一到滑坡体地下水位的变动，研究地下水位变动激发滑坡由间歇期进入滑动期相对于库水位变动和降雨的滞后性，并建立滞后响应方程。将滞后响应方程嵌入动力学方程中，结合地下水位预测序列建立基于地下水位变动的滑坡地表位移预测模型。研究成果对揭示水库老滑坡间歇性复活机制、发展位移预测模型和制定防灾减灾预案具有重要的科学意义。

库岸深层老滑坡在季节性降雨和周期性库水位变动联合作用下表现出间歇性复活特征。在这一复活过程中，滑动期与间歇期交替出现，滑带土经历不同速率的剪切和不同时长的固结。从滑动期内残余强度的剪切速率效应、间歇期内峰值抗剪强度的恢复特征以及间歇期过渡到滑动期的孔隙水压力触发过程 3 个方面着手，建立了描述库岸深层老滑坡间歇性复活的动力学方程。塘角村 1 号滑坡滑带土试样的环剪试验结果显示：残余强度在较小速率范围内表现出负速率效应，而当剪切速率达到一定值后残余强度不再减小，且有微弱增长趋势；峰值强度在短时间内有较明显的恢复，但在较小位移后衰减至残余强度；孔隙水压力触发剪切破坏的发生滞后于所施加的水压力，这一滞后过程为孔隙水压力的扩散过程。基于试验成果，根据所建立的动力学方程，对库岸深层老滑坡间歇性复活的动力学机制进行了讨论，从而为此类滑坡的预测和防灾减灾提供有价值的参考。将周期性库水位变动及季节性降雨入渗统一到滑坡体的地下水位变动，基于刚体极限平衡原理与Mohr-Coulomb强度准则，推导了描述库岸老滑坡间歇性复活过程的复活速率与地表位移预测模型。以三峡库区三舟溪滑坡为例，实测位移的比较结果显示预测效果良好，表明所建模型是合理的。.此外，处于破坏之前（或间歇期内）的滑带土经历瞬时蠕变和衰减蠕变阶段，并最终稳定在低速率的等速蠕变阶段。含水率对滑带土剪切蠕变速率的影响不甚明显，但含水率低于塑限时滑带土剪切蠕变模量最大。相同的剪应力下细颗粒含量高的试样具有更大的剪切蠕变位移。细颗粒含量较少的试样（40%细颗粒含量）与原始样相比较，具有明显的强度恢复特征，且固结时间越长，强度恢复越明显。