Damage evolution in sandstone under uniaxial cyclic loading and varying water contents: Theoretical and experimental investigation

Abstract

During underground excavation, the surrounding rock mass is subjected to complex cyclic stress, significantly impacting its long-term stability, especially under varying water content conditions where this effect is amplified. However, research on the mechanical response mechanisms of surrounding rock mass under such conditions remains inadequate. This study utilized acoustic emission (AE) and resistivity testing to monitor rock fracture changes, revealing the rock’s damage state and characterizing the damage evolution process during uniaxial cyclic loading and unloading. First, a damage variable equation was established based on AE and resistivity parameters, leading to the derivation of a corresponding damage constitutive equation. Uniaxial cyclic loading and unloading tests were then conducted on sandstone samples with varying water contents, continuously monitoring AE signals and resistivity, along with computed tomography scans before and after failure. The predictions from the damage constitutive equation were compared with experimental results. This comparison shows that the proposed damage variable equation effectively characterizes the damage evolution of sandstone during loading and unloading, and that the constitutive equation closely fits the experimental data. This study provides a theoretical basis for monitoring and assessing the responses of surrounding rock mass during underground excavation.

1. Introduction

During the construction of underground rock mass engineering, cyclic loads (such as blasting and excavation) may cause disturbance to the surrounding rock, leading to rock damage and ultimately causing catastrophic failure, thereby endangering the long-term safety of underground engineering [1, 2]. Rock damage not only affects its strength but may also have an adverse influence on its integrity and overall stability. Especially when sandstone exists in the rock mass, the increase in water content of the rock can lead to a decrease in its strength, resulting in reduced bearing capacity and stability of the rock mass, thereby significantly affecting construction safety [3, 4]. Therefore, studying the process of damage evolution in the rock with varying water contents under cyclic loading and unloading is of great significance for ensuring the safety of underground rock mass engineering construction.

In the field of rock mass damage evolution research, the methods for detecting rock mass damage are generally divided into destructive testing and nondestructive testing. Destructive testing methods include plastic strain testing [5, 6], energy dissipation monitoring [7], and dynamic modulus testing [1, 8]. The common feature of these methods is that they require a certain degree of damage to the rock mass to obtain data, and this damage may damage the underground rock mass structure and further aggravate rock mass damage. In addition, destructive testing is not conducive to in-situ dynamic monitoring, so it is limited in practical engineering applications. In contrast, nondestructive testing methods do not damage the rock mass and usually include acoustic emission (AE) monitoring [9, 10] and resistivity testing [11, 12]. These methods can provide real-time monitoring of rock mass damage without damaging the rock mass structure. Although destructive and nondestructive testing methods can both be used to characterize the degree of rock mass damage, since destructive testing may cause additional damage to the rock mass, nondestructive testing is more suitable for monitoring rock mass damage under cyclic loading and unloading.