Partition failure characteristics of rock material loading and unloading based on Mohr-Coulomb criterion

The stress state of a point in the material can be indicated by a Mohr circle and the different stress states of a point can be determined by charging stress circle under the coordinate system. The transformation of stress circle can be mainly divided into translation,flipping,radius expand and radius diminution. For rock material,these transforma- tions almost include all the processes of loading and unloading. Loading and unloading rate can be used to indicate the speed of transformation between different stress states,and it is not only the change of unit time,but also the change of unit space scale,such as unit length,unit depth,etc. Based on the Mohr-Coulomb criterion,this paper analyzed the rock materials loading and unloading processes under the states of compression-compression,tension-tension and ten- sion-compression,and found out the corresponding critical failure equation. On this basis, the relationship between time-weighted average loading and unloading rate of rock materials and the destruction level of rock materials were fur- ther obtained. According to the different time-weighted average loading and unloading rates,this paper also distinguish- ed whether the rock materials is destroyed. This research adopted the FLAC3D conventional three-axis numerical simu- lation experiments of seven different loading paths. The result showed when the material is damaged,the coincidence degree of the principle stress peak and the theoretical calculation result is as high as 98% . At the same time,this pa- per also conducted some simulation experiments under the conditions of seven kinds of axial and radial loading rates ratio and four types of loading rates. The test results indicated that the material is able to be destroyed when the ratio of the axial and radial loading rates reach within a certain range. The loading rate is positively correlated with the max- imum principal stress peak,which occurs at the state of material failure,and negatively correlated with the ratio of the maximum to the minimum principal stress.