Mechanical mechanism and morphological characteristics of fracture range formation in surrounding rock of soft rock roadway

After the excavation of the roadway, the broken expansion and shear expansion of the surrounding rock along the crack surface are the important reasons for the large deformation of the surrounding rock, and the broken expansion and shear expansion of the surrounding rock are closely related to the crack of the surrounding rock. It is of great significance to study the crack range of surrounding rock after roadway excavation and reveal the morphological characteristics of crack boundary for understanding the deformation range of surrounding rock and designing appropriate support scheme. Therefore, in order to study the crack range of surrounding rock after roadway excavation, based on elastic-plastic mechanics and sliding dynamics model of rock mass with single structural plane, the mechanical mechanism of crack formation, morphological characteristics of crack range and influencing factors of surrounding rock after roadway excavation were systematically studied by means of laboratory test, theoretical analysis and numerical simulation. The results show that the lateral pressure coefficient of surrounding rock has a great influence on the crack range of surrounding rock. Under the same surrounding rock conditions, when the lateral pressure coefficient of the surrounding rock is small, the crack range of the surrounding rock is circular and elliptical. When the lateral pressure coefficient of the surrounding rock is large, the crack range of the surrounding rock is also large, and it is butterfly-shaped. Under the condition of constant lateral pressure coefficient, the greater the buried depth of the roadway, the greater the range of surrounding rock cracks; However, the buried depth can not change the shape of the crack range of the surrounding rock, but only change its size; The smaller the cohesion and internal friction angle of the structural plane, the larger the crack range of the surrounding rock. Increasing the internal friction angle of the structural plane greatly reduces the crack range of the surrounding rock; Increasing the cohesion of the structural plane means that the range of surrounding rock cracks is not significantly reduced. When the stress direction of the surrounding rock changes, the crack range of the surrounding rock will rotate. When the butterfly leaf in the butterfly crack area rotates to the roof of the roadway, it will make the roadway prone to roof fall disaster, which is extremely unfavorable to the stability and maintenance of the roadway. According to the relevant research results, the surrounding rock control idea of optimizing the distribution of stress field + actively strengthening the self-bearing capacity of surrounding rock + dynamically regulating the support system is proposed. The 3DEC-BBM discrete element numerical model is used to study the distribution range and morphological characteristics of surrounding rock fissures after roadway excavation under different lateral pressure coefficients. It is verified that the numerical simulation results are basically consistent with the theoretical analysis results.