残积土的短时冻融累积损伤效应与边坡浅层多重失稳机制

Short-term frozen soil has the characteristics of great frequency of short- term freeze-thaw and high moisture content under the condition of snow infiltration. The results of the field investigation show that shallow collapse disease of residual soil slope occurred frequently. Unfortunately, the related basic theory has not been given enough attention. Taking short-term freeze-thaw cycles and snow infiltration as the main line，this project mainly studies on shallow multiple instability mechanism of residual soil slope induced by short-term freeze-thaw cycles and snow infiltration. The main content of the project is as follow：Firstly, strength damage model of residual soil and the freeze-thaw surface considering the change of moisture content and freeze-thaw cycles are proposed by laboratory test based on the monitoring data of climate environmental in short-term frozen soil area. Secondly, on the basis of model of soil macropore flow under the condition of snow infiltration and moisture-temperature coupling model considering the phase transition in short-term frozen soilt, the effect of moisture-heat coupling of residual soil slope under the condition of snow infiltration is revealed.Thirdly, the interaction mechanism of temperature field, moisture field, stress field and deformation field and multiple collapse mode of residual soil slope are analyzed by the coupling calculation model of the heat-moisture-stress fields and the field test under the condition of snow infiltration and short-term freeze-thaw cycles.The results of the research can provide a theoretical basis for disaster prevention and control of residual soil slope in short-term frozen soil area.

短时冻土具有冻融次数频繁、冰雪融化后土质含水率高等特点。现场调查表明，短时冻土区残积土边坡浅层冻融垮塌频发，但相关基础理论研究一直未得到重视。项目以短时冻融循环与冰雪融化入渗为主线，重点研究短时冻融循环与冰雪融化入渗诱发残积土边坡浅层多重失稳机制。具体为：基于短时冻土区气候环境监测资料与室内试验，揭示短时冻融循环下残积土与冻融界面强度累积损伤特性，提出随含水率和冻融次数变化的残积土与冻融界面强度参数累积损伤模型；构建考虑融雪入渗的土壤大孔隙两域渗流模型以及考虑相变的短时冻土水热耦合模型，揭示冰雪融化入渗下残积土边坡的水热耦合效应，并与室内土柱模型试验对比验证；基于考虑残积冻土损伤的水-热-力三场耦合模型，分析短时冻融循环与冰雪融化入渗条件下残积土边坡温度场、水分场、应力场与变形场多场相互作用机制以及多重垮塌模式，并开展现场试验验证研究。成果可为短时冻土区残积土质边坡的灾害防治提供理论依据。

短时冻土具有冻融次数频繁、冰雪融化后土质含水率高等特点。现场调查表明，短时冻土区残积土边坡浅层冻融垮塌频发，但相关基础理论研究一直未得到重视。项目以短时冻融循环与冰雪融化入渗为主线，重点研究短时冻融循环与冰雪融化入渗诱发残积土边坡浅层多重失稳机制。基于典型短时冻土区气候以及边坡墒情监测，表明短时冻区应重点关注边坡浅层10cm以内土壤强度的冻融损伤。若土壤冻结时间与太阳辐射时间相重叠或者气温处于土壤冻结温度以下的持续时间如小于1.5h，边坡土壤不易冻结。通过室内冻融循环实验，发现经历多次冻融循环作用后，残积土试样的应力-应变关系呈软化趋势，且在经历5次冻融循环作用后趋向于稳定状态；弹性模量、粘聚力及内摩擦角均发生损伤且损伤幅度均随着冷端温度的升高、含水率的增大、冻融循环次数的增加而增大；土体粘聚力损伤程度最大、弹性模量其次，内摩擦角损伤程度最小。建立的考虑冷端温度、含水率及冻融循环次数影响的弹性模量、粘聚力及内摩擦角非线性损伤模型与实验数据结果吻合良好。通过构建的考虑融雪入渗的土壤大孔隙两域渗流和非饱和渗流模型，发现大孔隙渗流相比于非饱和渗流对于边坡稳定性影响明显更大。增大大孔隙直径可增大大孔隙域与周围基质域的水分交换量，减缓水流的优先传导作用，从而使边坡稳定性降低。增加大孔隙长度，延长了水分的传导路径，削弱大孔隙域内水分的积累效果，对于边坡安全系数有一定影响。增加大孔隙弯曲率对于基质域含水率以及边坡安全系数影响可忽略不计。边坡安全系数与大孔隙间距之间存在安全系数最小的临界间距，间距过大导致大孔隙群的优先流效应无法发挥；而间距过小导致大孔隙间非平衡流相互叠加与干扰，削弱大孔隙的影响。基于冻土水-热-力三场耦合模型，分析了短时冻融循环与冰雪融化入渗条件下残积土边坡温度场、水分场、应力场与变形场相互作用机制以及多重垮塌模式。成果可为短时冻土区残积土质边坡的灾害防治提供理论依据。