Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling

This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading. Regarding the rock strength, the experimental study confirms that the peak strength ap and residual strength ar decrease as water pressure P increases. Especially, the normalized strength parameters ap/ apk and ar/are was negatively and linearly correlated with the P/a3. Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress ap(i) and crack damage threshold stress acd(i) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress-strain curves, indicating the unloading deformation modulus Eunload is larger than the loading deformation modulus Eload. Based on experimental results, a post-peak strength prediction model related to water pressure and plastic shear strain is established. CO 2023 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).