周期加卸载及反复干湿循环作用下非饱和土的本构模型研究

During the annual periodic fluctuation of reservoir water level, the ladder-shape deformations of bank slopes are caused by the influences of periodic loading-unloading and repeating dry-wetting cycle. In order to investigate the mechanism of bank slopes deformation and forecast their evolution progresses, the combination of theoretical analysis and experimental researches are adopted. Experiments will be taken on the silty clay of Three Gorges Reservoir bank slopes by the stress path triaxial system on unsaturated soil, to simulate the effects of reservoir water level periodic fluctuation and obtain the influence law on soil strain and saturation by the periodic loading-unloading change of suction and effective stress. And the interaction between moisture retention capacity and accumulated deformation of unsaturated soil will be analyzed under repeating dry-wetting cycle by the Soil-Water Characteristic Curve apparatus. Then base on the unsaturated soil mechanics and bounding surface plasticity theories, the coupling constitutive model of unsaturated soil will be established under the change of stress and hydraulic conditions, to reveal the continuous changes and coupling effects of stress-strain and suction-saturation relationship under periodic fluctuation of reservoir water level. Thus, the model can provide theoretical basis and technical support for more accurate deformation analysis and forecasting. The research results have great significances on theoretical researches and widely prospect on practical applications for deformation evolution analysis and geological disaster prevention of reservoir bank slopes.

水库运行期水位每年周期性涨落，岸坡土体在周期加卸载和反复干湿循环作用下发生不同程度的阶梯状变形。为探求变形的诱发机理、揭示变形的发展规律，本项目采用理论分析与试验研究相结合的方法，以三峡库区岸坡的粉质粘土为研究对象，通过非饱和土应力路径三轴仪模拟吸力和应力的周期性加卸载，获取非等向受压状态下非饱和土的吸力和有效应力周期性变化对土体变形及饱和度的影响规律，并借用土水特征曲线试验仪分析周期性干湿循环和固结压力作用下非饱和土的持水性能与累积变形的相互作用；然后沿用非饱和土力学的本构理论和边界面理论的双屈服面概念，建立应力与水力条件循环变化下的非饱和土耦合本构模型，从而揭示库水周期作用下岸坡土体应力-应变与吸力-饱和度的循环变化及相互影响规律。研究成果为更加准确地开展岸坡的变形分析预测提供理论依据和技术支持，对于库岸土质边坡的变形演化研究和防灾减灾处置具有重要的理论意义和广阔的应用前景。

三峡水库建成运行期，水库水位常年在145-175m变动，诱发库岸边坡发生不同程度的阶梯状变形。本项目从应力周期调整和反复干湿循环两个方面着手，以三峡库区巴东县赵树岭滑坡和白岩沟库岸为研究对象，开展了野外地质调查、现场位移监测、室内试验研究、理论分析及模拟等工作，主要研究成果为：1）、在超固结应力状态下的周期加卸载也会造成岸坡土体的持续累进变形，且每次变形增量随加卸载次数逐渐衰减，土体的强度也随之逐渐降低；2）建立了有效应力加卸载条件下超固结土的本构模型，揭示了土体减压屈服应力路径下土体强度发挥特性；3）固结压力下的干湿循环会引起土体发生体积收缩，且在第一次增湿阶段的变形增量最大，随后迅速减小且在经历3～4次循环后趋于稳定；4）构建了固结压力作用下干湿循环土水特征曲线的预测模型，分析了孔隙收缩造成非饱和土持水性能变化与累积变形发展的相互作用机理；5）整合并建立了周期加卸载作用下超固结非饱和土的耦合本构模型，揭示了吸力和有效应力周期性变化对土体变形及饱和度的影响规律；6）完成了库水周期变动下岸坡土体的变形累积过程模拟，通过对比分析探讨了库岸变形模拟中考虑周期加卸载作用的差异和重要性。项目研究成果加深了对三峡库区涉水滑坡和库岸的变形失稳机理的认识，为库水消落段岸坡的治理措施提供指导性建议。