Meso-experimental Research on the Initiation Process of Shear Band in Red Clay

Abstract： By using reconstructed Microcosmic Test System, and via the shear experiment on red clay in different water content rate and compaction degree, study the regularity of the inside micro-structure change of red clay in the process of initiation of shear band. The study demonstrates that: the process of red clay shearing includes the initial loading stage, the local deformation development stage, and the destruction stage. The initiation and development of shear band are at the anaphase of local deformation development stage, which is toward peak of stress. The process of initiation of red clay shear band could be described through the variation of fissure area ratio(FAR), fissure distribution fractal dimension(FDFD), roundness of particles(ROP) and particle orientation degree(POD). With the axial strains increasing, the FAR gradual increased, FDFD began to fluctuate in a narrow range and then increased gradually, ROP was steady at early stage, subsequently decreased, and then stable in the later stage, POD decreased gradually. Compared with lower Moisture Content, the red clay shear band with higher moisture content postponed the initiation time, the equal axial strains corresponded lower FAR and FDFD, as well as the POD and the initial value of ROP were both smaller. Along with the compactness increasing, FAR, FDFD, and ROP changed slightly, showing that interaction force between particles did not depend exclusively on extrusion and bite forces, and further illustrated the particularity of free oxides in red clay. Under high compactness, POD increased firstly and then decreased, while when compactness was low, POD showed digressive trend.