Improved Nishihara model considering the effect of moisture content on the whole shear creep process of shale

Abstract

The moisture content is closely related to the shear creep deformation behavior of soft rock, and the linear creep deformation behavior of soft rock can be described by the classical Nishihara model. However, the classical Nishihara model cannot describe the deformation characteristics of the whole process of shear creep including nonlinear deformation of rocks under the influence of moisture content. In this study, we presented an improved Nishihara model that connected a strain-triggered nonlinear dashpot in series on the classical Nishihara model to describe the whole process of rock creep, and a damage factor was proposed to reflect the effect of moisture content on the rock creep characteristics. The damage factors and related model parameters were determined from results of the shear creep tests, which were performed under four moisture conditions (0%, 0.46%, 0.87%, and 1.24%). The comparisons between model predictions and experimental results show that the improved creep constitutive model proposed here can not only describe the whole creep process well, but also reveal the influences of the moisture content on the creep behavior of rock, which demonstrate its accuracy and usefulness.