川东缓倾红层中降雨诱发型滑坡机制研究

STUDY OF MECHANISM OF LANDSLIDE INDUCED BY RAINFALL IN GENTLY INCLINED RED STRATUM IN EAST SICHUAN BASIN

四川盆地东部广泛分布着砂泥岩交替的缓倾红色地层,该类地层的倾角一般只有3°-10°,远小于层面或层间软弱面的内摩擦角。理论上,在该类地层中发生顺层滑坡的可能性较小。但实际上,川东红层中降雨诱发型顺层滑坡频发,给当地人民的生命财产安全造成极大的威胁。以四川省达县青宁乡滑坡为研究对象,通过现场调查与勘查建立滑坡地质模型;定性和定量分析滑坡发生前坡体内地下水渗流场和静水压力分布特征;在此基础上计算坡体在降雨作用下的稳定性变化;并通过环剪试验研究滑带土受滑体剪切过程中孔隙水压力和剪切强度变化特征。研究显示,川东缓倾红层滑坡是坡体内静水压力和滑带土剪切强度降低共同作用的结果。降雨入渗引起的水平推力和浮托力启动滑坡变形和缓慢滑动;滑带土受到滑体剪切,其孔隙水压力急剧上升,剪切强度急剧下降,最终导致滑体的急剧滑动。另外,研究认为久雨之后暴雨是滑坡发生的必要条件。研究结论具有一定的创新性,可以对川东红层缓倾角滑坡的预测预报与防治提供理论支持。

Gently inclined red stratum widely distributes in East Sichuan Basin. Dip angle of this type of stratum is always between 3°and 10°,which is far less than the friction angle between bedding planes. In theory,the bedding landslide is unlikely to occur in red stratum. But in fact,rainfall induced landslide in gently inclined red stratum occurs frequently, which leads to a huge threat to the local people. Taking Qingning landslide in Da County,Sichuan province as an example,the geological model through field investigation and exploration is built;then analyzes the seepage field and static water pressure distribution before the landslide;a slope stability was analyzed based on the results of above seepage analysis. In order to obtain the characteristics of pore water pressure and shear resistance,the sliding zone soil is sampled to conduct ring shear test. The results indicate that landslide is due to coupled action of water pressure and shear resistance decreasing of sliding zone soil. The horizontal pushing force and vertical uplifting force due to rainfall infiltration initiated the landslide to deform and slid slowly, and then shear resistance decreasing of sliding zone soil led to the rapid sliding. Furthermore, a longrainfall and then a strong rainfall are deemed to be the necessary condition of landslide. Conclusions of this paper are the new findings in this field and can supply theoretical support for landslide forecasting and prevention in East Sichuan Basin.