Analysis of deformation control mechanism of prestressed anchor on jointed soft rock in large cross-section tunnel

Prestressed anchorage systems have been gradually applied in the treatment of large deformation in soft rock tunneling. However, the research of support parameters on the mechanical behavior of large section cavern surrounding rocks with high joint density and deep buried high ground stress is not enough. In order to study the mechanical behavior of surrounding rocks under prestressed anchor support, a mechanical model is established. It is determined that the main controlling factors of the support effect are prestress, anchor cable length, and anchor cable spacing. Therefore, considering the distribution characteristics of surrounding rock joints, the discrete element simulation of different anchor cable lengths, circumferential spacing, and prestress is carried out. Similar simulation verification experiments further substantiated the accuracy of numerical simulation. The experimental results are applied to field engineering. The results indicate that the numerical simulation method of ubiquitous-joint and DFN (Discrete Fracture Network) can attain accurate results. The primary deformation and plastic zone of the tunnel is mainly located at the left shoulder of the inclined shaft, wherein the plastic zone is mainly tensile failure. The depth of the outer bearing arch, i.e., the length of the long anchor cable, is preferably 10 m. With the increase of circumferential spacing and prestress, the deformation and plastic zone of tunnel surrounding rock show a linear decrease. This paper can provide a theoretical basis for applying the prestressed anchorage system to control the large deformation of tunnel soft rock.