# Shear Mechanical Properties of Rock Joints Under Non-Uniform Load Based on DEM
## 1 Introduction  
Joints control the mechanical stability of rock masses [1], and their deterioration often leads to project destabilization, such as slope sliding and tunnel collapse, which seriously threaten life and property safety [2, 3, 4, 5]. Typically, slip along the contact interface is the predominant mode of joint failure [6, 7]. Therefore, investigating the shear mechanical properties of rock joints is imperative in computer-aided geotechnical engineering to understand potential hazards and formulate effective mitigation strategies.  
The shear mechanical properties of joints are influenced by various factors including overburden thickness, roughness, filling conditions, and rock yield [8, 9, 10, 11]. Numerous researchers have studied the impact of overburden loads on the shear mechanical properties of joints. For example, [PERSON], [PERSON] [12] investigated the effect of shear deformation on the hydraulic conductivity of joints under normal load boundary conditions and found a similar trend between hydraulic conductivity and the shear expansion of joints. [PERSON], [PERSON] [13] conducted shear tests on joints with different roughness with varying normal stiffness and infiltration pressure to reveal the hydraulic mechanism under normal stiffness (CNS)boundary conditions, considering effective normal stress interaction, normal stiffness, infiltration water pressure, and joint roughness. [PERSON], [PERSON] [14] performed multi-stage creep tests on joints under different normal stresses to uncover the influencing mechanism of normal stress on creep characteristics. [PERSON], [PERSON] [15] obtained factors influencing strength in jointed rock masses through a series of tests on structural surfaces under different circumferential pressures while proposing a criterion for strength under complex stress conditions. In terms of dynamics, [PERSON], [PERSON] [16] proposed two coupled loading methods, \"critical static stress + slight disturbance\" and \"elastic static stress + impact disturbance\", to reveal the mechanical mechanism of rocks under dynamic loading. [PERSON], [PERSON] [17] prepared tuff specimens under two conditions: natural air drying and saturation. [PERSON], [PERSON] [18] carried out uniaxial creep tests for 14.5 years to study the creep characteristics of rocks on a 10-year scale, analyzing the influence of water on rock creep mechanical properties based on indoor creep tests. [PERSON], [PERSON] [19] studied the shear properties of anchored joints under cyclic loading through laboratory shear tests, finding that the shear strength of bolted connections decreases more significantly than that of non-bolted connections.  
The existing studies have effectively elucidated the mechanical mechanisms of joints under various conditions. However, these studies have been conducted based on the assumption of uniformly distributed overburden loads. In reality, due to diverse boundary conditions, overburden thicknesses along the joints often exhibit variations, resulting in a non-uniform distribution of overburden load (Figure 1). In this study, to investigate the mechanical properties of joints under non-uniform load and establish a shear theory that reflects their actual state, we initially constructed a non-uniform-load mechanical model incorporating common forms of overburden load distribution in engineering applications using the strip partitioning method. Subsequently, we conducted a series of simulations to examine the shear mechanical behavior of joints using the DEM software PFC while focusing on the impact different load distribution forms have on shear mechanical parameters, crack development, and energy evolution laws. Finally, we developed a shear strength criterion under non-uniform load using machine learning techniques, providing theoretical support for stability assessment and the reinforcement of rock-related projects.  
Figure 1: Schematic diagram of non-uniform distribution of overburden load on joints.