降雨入渗路基边坡含水率变化分析

Analysis on Change of Moisture Content of Subgrade Slope under Rainfall Infiltration

降雨对黄土路基的影响与雨水的入渗深度密切相关,掌握雨水入渗深度和路基内部含水率的分布是分析降雨对路基稳定性影响的关键。基于土壤入渗的Richards偏微分方程,结合降雨路基水平入渗条件,建立了降雨入渗下路基的偏微分方程。基于泛函极值问题和变分法原理,显式地求解出路基中水分入渗过程微分方程的解,对不同降雨条件下黄土路基边坡的含水率变化进行了分析,并结合了不同含水率路基土试验结果的拟合方程。对一次降雨和连续降雨作用下,雨水入渗过程中路基上、中、下各部位含水率、黏聚力、内摩擦角的变化规律进行了分析。结果表明:路基水平体积含水率分布与位置距离和湿润峰距离密切相关;路基边坡内的含水率与垂直边坡路基深度呈非线性递减,内体积含水率在湿润峰处趋于稳定;路基上、中、下各部位的含水率变化规律不同,下部湿润峰最大,降雨入渗最深,影响最大,而上部最小;连续降雨与一次降雨含水率变化规律相同,但湿润峰的大小有所不同,路基的含水率并没有随着降雨的连续作用呈线性增加;随着降雨入渗的增加,路基含水率呈非线性降低,而黏聚力和内摩擦角均与含水率呈指数关系,当毛细作用力逐渐与渗透阻力达到平衡时,曲线出现突然增加的拐点。

The influence of rainfall on loess subgrade is closely related to the infiltration depth of rainwater. Mastering the infiltration depth of rainwater and the distribution of moisture content in subgrade is the key to analyze the influence of rainfall on subgrade stability. Based on the Richards partial differential equation of soil infiltration and the conditions of horizontal infiltration of rainfall subgrade, the partial differential equation of subgrade under rainfall infiltration is established. Based on the functional extreme value problem and the principle of variational method, the solution of the differential equation of water infiltration process in subgrade is explicitly solved, the change of water content of loess subgrade slope under different rainfall conditions is analyzed combining with the fitting equation of subgrade soil test result with different moisture contents. The variation rules of water content, cohesion and internal friction angle of the upper, middle and lower parts of subgrade in the process of rainwater infiltration under the action of one-time rainfall and continuous rainfall are analysed. The result shows that(1) The horizontal volume moisture content distribution in subgrade is closely related to the location distance and the distance of wetting peak.(2) The moisture content in the subgrade slope decreases nonlinearly with the subgrade depth of the vertical slope, and the volumetric moisture content tends to be stable at the wetting peak.(3) The variation rules of moisture content in the upper, middle and lower parts of the subgrade are different. The wetting peak in the lower part is the largest, the rainfall infiltration is the deepest, the impact is the largest, while those in the upper part are the smallest.(4) The change rule of moisture content of continuous rainfall is the same as that of one-time rainfall, but the size of wetting peak is different, the moisture content of subgrade does not increase linearly with the continuous action of rainfall.(5) With the increase of rainfall infiltration, the moisture content of subgrade decreases nonlinearly, while the cohesion and internal friction angle have the exponential relationships with the moisture content. When capillary force gradually reaches equilibrium with seepage resistance, the curve shows a sudden increase of inflection point.