Investigation of crack propagation and acoustic emission characteristics in jointed rock under freeze–thaw cycles based on DEM

Abstract

In cold-region environments, where complex stresses and mining disturbances occur, rock masses are frequently segmented into discontinuous bodies by fractured structural planes, leading to anisotropic physical and mechanical properties. To explore the evolution of microcracks, degradation characteristics, and failure modes of fractured rocks in cold regions under the influence of freeze–thaw cycles, integrating laboratory experiments with the damage mechanics of freeze–thaw cycles. A numerical model for freeze–thaw cycle damage in rocks with various fracture dip angles was developed. The study revealed that the freeze–thaw expansion force generated during the pore water–ice phase transition is the primary driving factor behind freeze–thaw cycle damage. The initiation and propagation of microcracks and micropores, the detachment of matrix particles, and the loosening of clay mineral structures result in the transformation of the rock from a dense to a porous state, causing significant degradation in macroscopic mechanical properties. As freeze–thaw cycles increase, both the uniaxial compressive strength and the deformation modulus of the rock decrease significantly, with the failure mode gradually shifting from brittle instability to brittle-plastic or plastic failure. The findings of this study offer a practical approach to uncovering the mechanical response mechanisms between freeze–thaw damage in fractured rocks and structural planes.

1. Introduction

Rock is a typical heterogeneous solid aggregate formed under various geological conditions, consisting of two primary components: structural planes and structures such as faults, joints, and fractures [1–4]. The natural defects within the rock not only alter its physical and mechanical properties but also influence the propagation paths of new microcracks. Moreover, these defects create channels for water infiltration and recharge, providing one of the essential conditions for freeze–thaw cycles—water [5,6]. Freeze-thaw cycles, as widely recognized, represent a physical process of water–ice phase transitions in the pore water inside the rock, driven by periodic changes in the natural climate of cold regions [7].

The freeze–thaw expansion force and pore water pressure generated during this process cause bonding failure between mineral particles within the rock, initiating and propagating new microcracks, and further extending pre-existing cracks. This leads to the degradation of the rock’s physical and mechanical properties, resulting in instability and failure, which can trigger geological disasters such as landslides, rockfalls, and debris flows [8–11]. Acoustic emission (AE) serves as a non-destructive dynamic monitoring technique, where AE event burst frequency and cumulative counts provide essential metrics for microcrack initiation rate and damage progression. With successive freeze–thaw cycles, microcracks extend and link within stress concentration zones, resulting in increased AE signal energy. Through mapping the spatial distribution of AE energy and peak amplitudes, the spatiotemporal evolution of energy release during crack propagation can be quantitatively depicted, thus identifying the critical threshold of rock instability and failure [12]. Therefore, investigating the microcrack propagation and acoustic emission characteristics of rocks under freeze–thaw cycles is crucial for accurately assessing the stability and safety of engineering in cold-region rock masses.