Weakly cemented coal measures are widespread in western China (Zhang et al., 2015, Meng et al., 2016). However, its diagenesis environment in Western China was different from that in central and eastern China (Wang et al., 2019,). The insufficient diagenesis results in the low strength, easy disintegration, easy weathering, poor cementation of the weakly cemented rock; once exposed to water, the weakly cemented rock tend to be muddy (Meng et al., 2015, Bai et al., 2020). As a result, the failure, rupture, and fracture of the surrounding rock under the mining disturbance in the western mining area are different from that in the central-eastern mining area (Yang et al., 2017, Zhang et al., 2018). When the macroscopic cracks of weakly cemented rock are not through, the rock can be considered as an entirety. When the collapse failure occurs, the rock becomes a loose mass, which has a great relationship with the cementation performance of the rock. Bond strength is an important index to characterize the performance of rock cementation. The mechanical properties and failure mode of weakly cemented rocks can be further explored by studying the relationship between bond strength and rock strength.
The particle flow discrete element method has been widely used to study microscopic mechanical properties of the rock. In the PFC program software, the particle flow discrete element method is used as the basis for the theory, the rigid bodies with masses are used as particles, and the interaction motion and force action between particles are studied to solve the macroscopic and complex practical problems (Shimizu et al., 2010). At present, the relationship between micro-parameters and macro-mechanical properties of rocks had been studied by PFC software (Potyondy and Cundall, 2004, Hsieh et al., 2008, Kazerani and Zhao, 2010, Su et al., 2011, Yi et al., 2011, Zhou et al., 2012, Obermayr et al, 2013, Zhang et al., 2016, Zhang et al, 2019, Wang Min, 2020). ABi analyzed the quantitative relationship between micro-parameters and the macro-parameters by means of variable control, and the results of the laboratory tests were consistent with those of the numerical simulation, indicating that micro-parameter results are reliable (ABi et al., 2018). Cong analyzed the correlation between the macroscopic mechanical characteristics of the rock and the microscopic parameters through the loading and unloading tests on the marble. The elastic modulus of the parallel bond was linearly related to the macroscopic elastic modulus; in particular, the secondary failure surface of the rock sample decreases with the increase of the friction factor (Cong et al., 2015). Zhao discussed the influence of some microscopic parameters of the parallel bonding model on the macroscopic deformation parameters (Zhao et al., 2012). Su analyzed the effect of particle size on macro-mechanical properties by uniaxial compression simulation tests (Su et al., 2018). Through different experimental design methods, Yoon obtained microscopic parameters that have a significant influence on the failure characteristics of the model (Yoon J, 2007). By numerical experiments, Yang fitted the approximate expressions of the compressive strength, elastic modulus, and Poisson’s ratio of the parallel bonding model (Yang et al., 2006). Xu developed a fine-scale structural model of limestone and obtained the microscopic parameters mechanical parameters of limestone (Xu et al., 2011). Through uniaxial compression and Brazilian splitting tests, Deng concluded that the peak strength of hard rocks was mainly influenced by the bond strength (Deng et al., 2019). In previous studies, the relationship between macroscopic mechanical properties and micro-parameters of rocks was discussed from different perspectives. It was pointed out that microscopic parameters determine the mechanical behavior characteristics of rocks. Hard rocks were mainly studied in these studies, while soft rocks have been rarely discussed. In western China mines, the rock strength of most coal seams is relatively low, and the surrounding rock of roadways is subject to frequent deformation. It is of guiding significance for roadway support to deeply study the influence of the weakly cemented rocks (Wang et al., 2017, Meng et al., 2014).
Considering the real conditions of weakly cemented rocks in western mining areas, the influence of the bond strength on the peak strength and the failure mode of rock were investigated through numerical simulation. This paper provides a basis and reference for further understanding of the relationship between the strength of weakly cemented rocks and the development of cracks in surrounding rocks after engineering disturbances.