南江红层地区缓倾角浅层土质滑坡降雨入渗深度与

2011年“9.16”特大暴雨诱发四川省南江县发生数以千计的缓倾角浅层土质滑坡，该类典型滑坡具有滑体厚度集中在1～5 m区域，且总是沿呈“光面”的基覆界面顺层滑动的特殊性。通过设计室内降雨入渗试验、建立G-A入渗模型及考虑大气对土坡的影响计算得大气影响深度，分析滑坡降雨入渗深度，研究滑体厚度分布成因；并根据非饱和土强度理论分析天然状态下及降雨条件下浸润峰分别位于土层中与基覆界面时的斜坡稳定性，研究滑坡沿基覆界面滑动成因。结果表明：南江县红黏土渗透性极低，短时间的强降雨下降雨入渗深度十分有限，一般仅入渗50 cm左右。研究区的大气影响深度为5.37 m，在该深度范围内，雨水易入渗，但随着深度的增加，土体风化程度逐渐减弱，土体孔隙比、渗透性逐渐降低，入渗逐渐困难，直至下覆基岩，降雨过程中雨水入渗深度是导致缓倾角浅层土质滑坡厚度主要集中在1～5 m的原因。在降雨条件下，当浸润峰深度小于土层厚度，潜在滑面位于浸润峰处时，斜坡保持稳定，当浸润峰深度等于土层厚度，潜在滑面位于基覆界面时，界面滞水，水位上升，孔压产生，同时界面岩土体发生软化和润滑作用，界面效应是导致滑坡沿基覆界面这一“光面”顺层滑动的主要原因。

Rainfall infiltration depth and formation mechanism of slow-inclination soil landslides in Nanjiang

Lots of slow-inclination soil landslides were triggered by the rainfall on September 16th in 2011 in Nanjiang. The typical landslides have sliding bodies with thickness concentrated in 1~5 m, and they always slide along the bedrock cover interface which is a smooth surface. By designing rainfall infiltration tests, establishing G-A infiltration model and calculating atmosphere influence depth considering the effect of atmosphere on the slope, the rainfall infiltration depth of landslides is analyzed, and the distribution causes of sliding thickness are investigated. The slope stability is analyzed based on the unsaturated soil strength theory when the infiltration peak is located in the soil layer and the base cover interface under the natural and rainfall conditions. The results show that the permeability of red clay in Nanjiang is extremely low, the rain infiltration depth is very limited in short and heavy rainfall, and it is generally only about 50 cm. The atmosphere influence depth is 5.37 m in the study area. In this range the rain easily infiltrates. However, with the increase of depth, the weathering degree of the soil is gradually weakened, the pore ratio and permeability gradually decrease, and infiltration is gradually difficult until the bedrock. The rainfall infiltration depth is the main cause of the typical landslides with shallow slide. Under rainfalls, when the depth of infiltration peak is less than the thickness of soil layer and the potential sliding surface is in the infiltration peak surface, the slope is stable. When the depth of infiltration peak is equal to the thickness of soil layer and the potential slip surface is located on the base cover interface, stagnant water at the interface is generated, the water level rises, the pore pressure increases, and the interface produces softening and lubrication. The interface effect is the main cause for the slow-inclination soil slide along the bedrock cover interface which is a smooth surface.