Study on the dilation characteristics of silty mudstone under triaxial compression

Abstract

The volume dialation effect is a significant characteristic of rock volume change under triaxial compression conditions, and is an important manifestation of the nonlinear expansion of rock volume. In order to examine the dialation characteristics of rock, analyze the influence mechanism of plastic characteristics and stress level on the dialation characteristics, and explain the deviatoric stress-strain curve characteristics of the rock in the whole process, taking the silty mudstone of a water diversion project in southwest China as the research object, a study was carried out. In the triaxial compression test under the confining pressure level of 1~25 MPa, the Mohr-Coulomb strength criterion and plastic parameters were introduced to study the dialation characteristics of the rock. The results show:(1) The dialation stress and residual stress of the rock are 0.65 and 0.58 of the peak stress respectively, and various strength indicators have an obvious linear relationship with the confining pressure level, which is consistent with the Mohr-Coulomb strength criterion;(2) After dialation occurs, the internal friction angle and cohesion of the rock experienced changes that first increased and then decreased as the plastic parameters increased, and the change characteristics had a certain degree of asynchrony. The fitting model based on the Mohr-Coulomb strength criterion and plastic parameters can Describe the deviatoric stress-strain curve of the whole process after the rock dialation occurs;(3) The dialation angle and dialation index decrease in a negative exponential manner as the confining pressure increases, and the rupture surface inclination angle gradually increases with the increase of the confining pressure. and gradually stabilized.The deformation process of rock after dialation is closely related to the stress level and plastic properties, and the confining pressure has an inhibitory effect on rock dialation.

Keywords

triaxial compression test / dilation / Mohr-Coulomb strength criterion / characteristic stress / dilation index