水位变动下岸坡欠饱和土体水力耦合效应及滑坡机理研究

There are a great number of Hydropower Stations that either have been completed or are under construction/planning. The operations of these giant hydropower facilities can lead to substantial alterations to the external water environment. The frequent fluctuations of water level have resulted in a large volume of landslides. Reservoir slopes failure can greatly affect the operation of hydropower, and pose threats to the safety of dams, thus leading to the economic loss. The mechanical properties of soils in the slope, which are originally in partially saturated state, are closely related to its degree of saturation, the water retention behavior of the soil, in turn, depends on its mechanical deformation. The rise and drawdown of water levels in the reservoir can lead to change in both the flow regime and stress-strain fields within the slopes. The coupled hydro-mechanical behaviors are responsible for the ultimate failure modes of the reservoir slope, which is also controlled by the time-dependent(creep) behaviour of unsaturated soils near the critical slip surface. In this project, the elemental tests, constitutive modelling, numerical simulation and field investigation will be combined to study this double-level coupling behavior (hydro-mechanical coupling at elemental level, and coupling between seepage and deformation fields at global level). The project will start with laboratory tests on the mechanical creep behaviour and hydraulic properties. Then, the Elasto-Visco-Plastic constitutive models for unsaturated soils will be proposed and calibrated. An effective and robust numerical scheme will be developed to integrate the new models. The numerical simulation using UNSATCON (developed by the applicant) and field study will be conducted and compared. Based on results, the double-level hydro-mechanical coupling effect and its influence on the failure mechanisms of reservoir slope will be ascertained. The project will end up with the methodology for evaluation of reservoir landslides hazard, the measures for prevention of slope failure. The outcomes are expected to serve as references for the operation and management of the hydropower stations.

我国规划、在建和已经建成水电站数量庞大。大型水利工程的运行极大地改变了岸坡原有水环境，诱发了众多的滑坡，造成经济损失，威胁大坝安全。库岸边坡潜在滑动土体原处于欠饱和状态，欠饱和土体的力学特性与饱和度密切相关，其持水能力也受到土体形变的影响。库水位波动改变岸坡内部渗流场和应力场，破坏原有平衡状态。库区滑坡即受欠饱和土体水力耦合响应的控制，也受到滑带土蠕变（率相关）特性的影响。这些特性决定了坡内耦合的渗流场与变形场时空演化的复杂性。本项目通过单元体试验、本构模拟、数值分析、并辅以现场试验揭示这一双重耦合效应（土单元水力耦合及其率相关性，耦合的渗流场和应力/变形场）对岸坡失稳的影响机制。通过室内试验研究欠饱和土的耦合及蠕变特性，建立粘弹塑性水力耦合本构模型；利用自编UNSATCON数值平台模拟渗流场和变形场的时空演化规律。整合分析结果，揭示库水位波动下岸坡失稳机理。

我国规划、在建和已经建成水电站数量庞大。大型水利工程的运行极大地改变了岸坡原有 水环境，诱发了众多的滑坡，造成经济损失，威胁大坝安全。库岸边坡潜在滑动土体原处于欠饱和状态，欠饱和土体的力学特性与饱和度密切相关，其持水能力也受到土体形变的影响。库水位波动改变岸坡内部渗流场和应力场，破坏原有平衡状态。本项目通过试验、本构理论和数值分析、并辅以现场试验揭示水位变动滑坡至灾机理。通过室内试验研究欠饱和土的水力耦合特性，基于对UNSATCON数模结果的深度分析提出了土体渗透系数的简化确定方法，方法精度高，可提高数模精度；提出了全新的三维边坡稳定分析方法，并应用于几个实际工程，结合现场数据分析，建立了库水位变动下土坡渗流-应力耦合场数值模拟模型，揭示库水位上升过程中岸坡的后退式滑动机理。