干湿循环效应下残积土孔隙演化特征及降雨滑坡机制研究

Rainfall-induced landslides often caused catastrophic disasters, and such disasters regularly bring about significant casualties and property losses. For this reason, the mechanism of rainfall-induced landslides was a key problem urgently to be solved by the field of rock and soil mechanics and disaster prevention and mitigation. Combined with the unsaturated soil mechanics theory and numerical simulation, a serials micro test would be used to study the evolution of pore structure of residual soil under drying and wetting cycles based on the micro-macro method. The microscopic and macroscopic quantitative characterization for the co-evolution of the hydraulic characteristic and pore structure would be proposed, and the SWCC microscopic model considering the effect of wetting and drying cycles and deformation would be established, then the function between the permeability and porosity and water content of residual soil would also be developed, to describe the variation of the micro pore structure and macro water content and mechanic behavior in residual soil. A mathematical model for describing the pore structure and deformation evolution of residual soil under the effect of wetting and drying cycles would be preliminary constructed, the analysis method of rainfall infiltration and stability evolution of residual soil would be established at the same time, to simulate the temporal and spatial variation of the distribution of residual soil porosity and deformation. The geomechanical model would be also used to reveal the mechanism of rainfall-induced landslides. The above research would improved the multi-phase seepage theory, provided theoretical support and technical platform for rainfall-induced landslides disaster prevention and disaster reduction decision.

降雨滑坡灾害每年均造成巨大的人员伤亡和经济损失，其致灾机理是岩土力学和防灾减灾领域迫切需要解决的关键问题。本课题以非饱和残积土为研究对象，采用理论研究、数值仿真及宏观与微观分析相结合的方法，通过一系列室内微观试验，研究干湿循环效应下残积土微观孔隙结构演化特征；提出残积体孔隙结构与水力特性协同演化过程中微观到宏观的定量表征方法，建立考虑干湿循环效应和变形效应的SWCC微观模型，推导干湿循环效应下土体固有渗透率-孔隙率-含水率的协同表征模型，实现基于干湿循环效应下土体孔隙结构与宏观体积含水率及力学行为之间的定量描述；初步构建描述干湿循环效应下残积土孔隙结构及变形演化耦合数学模型，建立残积土坡对降雨入渗响应与稳定性演化分析方法，结合地质力学模型，揭示降雨诱发土坡失稳机制，实现干湿循环效应下残积土孔隙率及变形时空演化过程的定量预测。研究成果可进一步丰富和完善多相渗流理论，同时为降雨诱发滑坡灾害防治与减灾决策提供理论支撑和技术平台。

湿热环境是影响残积土工程性质的重要因素。通过核磁共振、压力板仪、非饱和三轴排水剪切试验和数值分析等手段，研究干湿循环作用下残积土的微观孔隙演化规律、持水性能及抗剪强度劣化规律，分析水-力耦合及干湿循环效应下浅层土坡孔压、湿润锋及安全系数的时变特性，探讨土坡失稳破坏机制。主要成果有：(1)提出干湿循环效应下残积土微观孔径分布动态演化模型，随着干湿循环的进行，土体孔隙度呈指数上涨，T2谱面积呈对数上升。干湿循环作用下，土体内部可溶性矿物和胶结物质流失，聚集体间联结散失、孔隙连通，发育成大孔；聚集体内部颗粒间小孔隙逐渐粗化，发育成大一级的介孔或大孔，导致土体微孔占比降低。(2)提出考虑应力和吸力引起孔隙比变化的修正Van Genuchten模型，所提模型参数具有明确的物理意义，对塑性指数为11~31的土体具有很好的适用性；建立模型参数与干湿循环次数间的函数关系，初步构建干湿循环效应和变形效应的SWCC和HCF微观模型。(3)随着干湿交替的进行，表征土体强度特性的指标(总黏聚力、有效内摩擦角、吸力摩擦角、饱和抗剪强度及有效应力参数)均呈不同程度的下降。整个干湿循环周期内，聚集体间持续被破坏，饱和抗剪强度持续减小；而聚集体内部颗粒联结破坏滞后，吸力摩擦角的下降缓慢，甚至趋于稳定。(4)基于降雨诱发残积土坡失稳模型试验，开展不同工况下SWCC曲线过渡区吸力与含水率相关性以及入渗率和湿润锋变化规律研究，提出湿润锋修正Lumb公式；基于坡体变形和吸力时变规律，分析土坡前端推力对降雨入渗的响应，提出边坡变形发展以及坡体前端推力变化的3个阶段。(5)干湿交替初期，边坡可因正孔隙水压力的增加而失稳；干湿交替后期，湿润锋的快速推进加剧基质吸力迅速丧失及土体强度下降，边坡安全系数显著降低，边坡失稳破坏时间也越短。因此，可将湿润锋处的安全系数(局部最小值)作为控制边坡长期稳定性的临界值。