Micro-characteristics of strength reduction of tuff residual soil with different moisture

Abstract

The weathered residual soil slope formed by the long term weathering of large igneous rock mass under the impact of abundant rainfall in southern China is prone to instability and deformation, causing wreak havoc. Therefore, it is very important to study the internal mechanisms of its instability and deformation induced by rainfall based on its special structural properties. In this paper, we 1) analyzed its mineral compositions using X-ray diffraction method, 2) obtained its shear strength parameters through quadruplet direct shear tests in the conditions of different moisture contents and dry-wet cycles, 3) studied its microstructure using Scanning Electron Microscopy (SEM), 4) quantitatively studied its porous distribution with the help of MATLAB image processing toolbox, and 5) established the fitting curve of fractal dimension and soil shear strength parameters of the tuff residual soil of Qishan landslide zone in Yongtai County, Fujian Province, China. The results indicated that 1) tuff residual soils are rich in clay minerals with lamination as the dominant microstructure, 2) moisture content and dry-wet cycle significantly affect soil microstructures as characterized with decreased pore size and increased pore number, and 3) soil mass has obvious fractal characteristics, the shear strength decreases gradually with the fractal dimension increasing and the fractal dimension has greater impact on soil cohesiveness than the angle of internal friction.