水热耦合作用下季节冻土边坡降雨入渗规律及入渗机理

Study on Rainfall Infiltration Law and Mechanism of Seasonal Frozen Soil Slope Under Hydro Thermal Coupling Effect

为研究春融期降雨工况下季节冻土边坡水热迁移规律及降雨入渗机理,选取季节冻土区高速公路路堤边坡为研究对象,基于非饱和冻土水热迁移耦合模型结合降雨入渗边界条件,提出了降雨入渗条件下冻土边坡水热耦合理论与数值计算方法,并通过COMSOL有限元仿真软件对冻土边坡降雨入渗过程进行计算,分析不同降雨强度、初始含水率对冻土边坡体积含水率、温度、入渗率、湿润锋变化影响规律,同时开展冻土边坡降雨入渗模型试验研究,并将试验结果与数值模拟结果对比分析,验证了数值方法合理性。研究结果表明:中雨、大雨强度降雨持续12 h后,降雨入渗深度可达50 cm,受非饱和状态及孔隙冰阻碍渗流通道影响,降雨初期冻土边坡入渗率极低,随着冻土逐渐融化,入渗率逐渐提高;水热迁移耦合模型可较好体现降雨强度、初始含水率对于冻土边坡水热状态变化的影响规律,降雨强度越大,冻土边坡含水率上升越快;初始含水率越高冻土边坡中体积冰含量越高,降雨前期边坡体积含水率变化较慢,后期变化速度加快,初始含水率越大,温度上升迟缓现象越明显;相较于常温边坡降雨入渗规律,冻土边坡湿润锋增长速度呈现明显的初期缓慢-加速-放缓三段式发展,湿润锋深度在10 cm以内变化缓慢,湿润锋深度增大至10 cm后增长迅速,超过20 cm时增长再次放缓。

In order to study the law of moisture and heat migration and the mechanism of rainfall infiltration in seasonal frozen soil slope during the spring thaw period,the research taking the highway embankment slope in seasonal frozen soil area as the research object.Based on the combination of unsaturated soil moisture-heat migration model and the boundary conditions of rainfall infiltration,the theory and numerical calculation method of moisture-heat coupling model of frozen soil slope under the condition of rainfall infiltration are put forward.The rainfall infiltration process of the frozen soil slope was calculated through the COMSOL finite element simulation software.The influence of rainfall intensity and initial moisture content on the volumetric moisture content,temperature,infiltration rate,and wet front of the frozen soil slope was analyzed.Simultaneously,a model test of rainfall infiltration on frozen soil slope is carried out.The experimental results are compared with the numerical simulation results to verify the numerical value.The results show that the depth of rainfall infiltration can reach up to 50 cm after 12 hours of moderate rain and heavy rain intensity.Affected by the unsaturated state and pore ice obstructing the seepage channel,the infiltration rate of frozen soil slopes at the beginning of rainfall is extremely low.As the frozen soil gradually melts,the infiltration rate gradually increases.The moisture-heat coupling model can reflect the influence of rainfall intensity and initial moisture content on the change of the state of frozen soil slopes.The greater the rainfall intensity,the faster the moisture content of frozen soil slopes will rise;The higher the initial water content,the higher the volumetric ice content in frozen soil slopes.The slope volumetric water content changes slowly in the early period of rainfall,and the rate of change increases in the later period.The greater the initial water content,the more obvious the slow temperature rise.Compared with the law of rainfall infiltration on ordinary slope,the growth rate of the wet front of frozen soil slopes first increases and then decreases.The depth of the wet front changes slowly within 10 cm.The wet front depth increased to 10 cm and then increased rapidly.When it exceeded 20 cm,the growth slowed down again.