Shear Creep Tests on Fissured Mudstone and an Improved Time-Dependent Model

Abstract

All rocks undergo creep when under a long-term load, and shear sliding is a major failure mode of natural slopes. However, the mechanical properties of fractured mudstone differ from those of intact rock. To investigate these properties and the influence of normal stress and pre-cut crack length on mudstone shear creep characteristics, we performed shear creep tests on fractured mudstone. The experimental results show that axial load magnitude and crack length have a marked influence on the rock’s shear creep behavior. The larger the axial compressive stress, the smaller the shear creep deformation. The longer the crack, the more significant the shear creep deformation. When stress is low, existing creep models can reflect the creep properties of mudstone well. However, most published creep models cannot accurately portray the nonlinear creep behavior of mudstone in a tertiary creep stage. We propose an improved time-dependent creep model that overcomes the shortcomings of the traditional models in describing nonlinear creep. The new model has fewer parameters and can be applied to practical engineering problems involving soft rock. During the shear creep tests on soft argillaceous samples under different loads, shear failure zones in fractured mudstone exhibited both gradual and sudden failure. The shear time-dependent model for mudstone developed in this study can effectively explain mudstone instability.