Experimental Study on Loess Mudflow Induced by Rainfall in Yan′an Area

The changes of grain size distribution and microstructure of loess after rainfall were investigated in this study,as well as their effects on the initiation of mudflow.A simulated rainfall experiment was conducted in field for this purpose.We found that after rainfall,the volumetric percentages of fine and rough clay particles increase approximately 22% and 18%,and those of silt and fine sand decreased 7.6% and 3.3%,respectively,in the samples collected from the sediment deposits.Consequently,the grain size of residual loess on the slope coarsened and the connection of loess skeleton became loose after rainfall.Such changes of grain size and microstructure of loess induced by rainfall implies that both of the shear and pressure resistance of loess will decrease after rainfall.Thus,the probability of the mudflow initiation increases.Once the balance between the gravitational component of loess along the slope and the shear resistance is broken as the rainfall penetrates,the loess begins to slip and possibly develops into mudflow.Preventing the loess on the slope effectively from being coarsened is the key to mitigate water loss and soil erosion.