Brittle and ductile creep behavior of Jinping marble under true triaxial stress

Abstract

With excavation during deep underground engineering, the rock mass near the sidewall changes from ductile behavior to brittle behavior. However, the ductility of the rock mass at a certain distance from the sidewall may increase due to the change in stress. Over time, the failure mechanism of the rock mass is not necessarily consistent. The aim of this study is to obtain a better understanding of creep mechanisms under 3-D stress states. To achieve this goal, six brittle creep and two ductile creep experiments on Jinping marble were conducted under true triaxial stress conditions (σ1 > σ2 ≥ σ3). The test results show that creep deformation of rock decreases with increasing intermediate principal stress. Many micro-cracks were observed by scanning electron microscopy in the samples failed under the ductile creep. However, brittle creep and ductile creep present different crack expansion modes in microscopic terms, resulting in significant differences in macroscopic deformation behavior. The steady creep rate increases slowly with increasing σ1-σ3 when brittle creep occurs. Meanwhile, when the stress reaches a certain value during ductile creep, the steady creep rate suddenly increases exponentially from 10−6 h−1 to 10−5 h−1. From the test results, we can deduce that the true triaxial stress and time effects play key roles in the creep behavior of rock masses in deep engineering projects.