A novel approach for applying active surface pre-stress on surrounding rocks of roadways by backfilling behind surface support

Abstract

In response to the poor active support effect of the surface protection components in soft coal roadway and the continuous expansion of the broken range of local exposed surrounding rock, which leads to the failure of anchor rod and cables, a mesh grouting surface type prestressed application technology has been developed. The authors conducted post mesh grouting tests on different specifications and models of metal mesh, and obtained the mechanical response characteristics of the support system during the application of active surface prestressing. Based on this, the post mesh grouting tests on the roof and two sides of the mesh under on-site conditions were carried out, verifying the applicability of post mesh grouting technology. The research results indicate that: ① There is a gap between the metal mesh and the coal wall, which leads to poor active support ability. The continuous expansion of the broken range of the exposed surrounding rock is the main controlling factor for the failure of anchor rod and anchor cable support. Filling the uneven structure around the contact surface between the metal mesh and the coal wall, increasing the active support ability of the protective surface components, and comprehensively sealing the surrounding rock are the technical means to improve the anchor mesh support system; ② Injecting and filling between the metal mesh and the surrounding rock can achieve the application of surface active pre-stress. The trend of surface stress change is mainly divided into: the initial stage of constant surface stress, the stage of increasing surface stress, and the stage of reducing surface stress to stable state; ③ During the process of grouting behind the mesh, the trend of changes in surface stress values is closely related to the grouting pressure and deformation of the metal mesh. During the process of increasing surface stress, the grouting pressure and deformation of the metal mesh also increase accordingly; ④ Grouting behind the mesh can effectively alleviate the stress concentration of the cable tray. During the process of increasing the surface stress value, the pre-tightening force of the cable with stress concentration can show a small decrease trend, while the pre-tightening force of the cable with relatively uniform stress shows a synchronous upward trend during the process of increasing the surface stress value. The technologies developed are expected to become supporting technologies for rock bolt support, providing technical and theoretical references for the treatment of complex and difficult roadway.

Keywords

• rock bolting
• metal mesh
• backfilling behind mesh
• surface active pre-stress
• ground control