## 1 Introduction
(2017) conducted indoor experiments to investigate the compressive creep behavior of broken rock masses with different lithologies and proposed a creep constitutive model. Due to the limitations of indoor experiments to visually demonstrate the complex internal deformation processes of broken rock mass, numerical simulation methods were used to study the stress redistribution and spatiotemporal evolution of secondary fracturing within broken rock blocks ([PERSON] et al., 2018; [PERSON] et al., 2020). [PERSON] et al. (2020) employed a two-dimensional discrete element numerical simulation method to compare the creep behavior of broken rock masses composed of rounded aggregates and irregular aggregates under uniaxial compression and direct shear loading conditions, respectively. Furthermore, they investigated the distribution characteristics of force chains within broken rock masses through key aggregates. [PERSON] et al. (2021) established a three-dimensional numerical model using the discrete element method (DEM) for triaxial compression of broken rock mass, proposed a long-term prediction model for bulking factor, and provided initial explanations for the principles of particle interlocking during triaxial compression. [PERSON] et al. (2022) employed a combined approach of three-dimensional discrete element numerical simulation and experimental methods to quantitatively analyze the evolution characteristics of stress, porosity, and breakage rate of broken rock blocks in the process of lateral confinement compression within goat. The perspective of flow through a cracked or porous medium has recently emerged as a prominent research area. [PERSON] et al. (2023) compared heterogeneous porous media, such as broken rock mass, with homogeneous porous media and concluded that the distribution of dominant flow channels has a greater influence on fluid flow patterns and pressure distribution. [PERSON] et al. (2024) experimentally investigated the compaction characteristics, fracture growth law, and permeability evolution of broken coal-rock mass under seepage effects. [PERSON] et al. (2025) developed a heat exchange test system for broken rock mass using CO\({}_{2}\) as a substitute for heat transfer fluid, demonstrating that higher porosity in broken rock mass leads to improved energy storage efficiency. [PERSON] et al. (2026) used the discrete element method (DEM) to track particle migration trajectories within broken rock masses, revealing their migration laws and proposing a method to determine their migration states. In the process of thermal mine water extraction, the impaction of small rock particles on rock blocks will affect their fracture propagation and fracture law. However, there is currently limited research on the migration and impact of detached small-size particles from broken rock mass within the void structure and their influence on the overall structural strength. Therefore, it is necessary to discuss the detachment, migration, and impact of small-sized particles of broken rock mass in geothermal water storage in the goat of the abandoned mine so as to obtain deformation and fracture characteristics of broken rock mass that are more in line with engineering practice. This study proposed a computational model for impact strength erosion based on the bonding weakening method in discrete element particles and subsequently conducted the secondary development of a three-dimensional numerical calculation model for broken rock mass under lateral compression within abandoned mine goat. Hence, the strength erosion effect of small particles on rock mass is taken into account for the first time in the numerical simulation of particle discrete elements, and the method of simulating the fracture behavior of broken rock mass with discrete elements is innovatively presented. On this basis, the deformation, fracture patterns, and acoustic emission (AE) characteristics of broken rock masses with different size grading distributions considering impact strength weakening were studied.