Space-time effect of zonal disintegration in deep buried rock mass considering the backing plate effect

Zonal disintegration is a complex spatiotemporal evolution process of deep rock mass under the com-prehen- sive action of many sensitive factors. The pre-stressed full-length anchoring bolts which were adopted for the initial support of the surrounding rock of the deep underground cavern were taken as the study object. The study considered the influence of supporting plate under different reacting forces on the strength parameters of the surrounding rock and established a mechanical analysis model about the coordinated deformation occurred between the bolt body and sur- rounding rock. A calculation formula for determining the position of neutral points along bolt body on the condition of zonal disintegration was deduced. Furthermore,the inversion analysis for the zonal thicknesses,broken ranges as well as quantities under different support plate reaction forces was carried out. According to the non-linear rheological mod- el and the maximum deviatoric stress along the tangential and radial directions of the rock mass at the elastic-plastic interface,a theoretical formula used to determine the fracture occurrence moment of the rock mass was proposed. The results show that ① under the condition of zonal disintegration,the coordinated deformation occurs between the sur- rounding rock of deep buried cavern and the pre-stressed anchor body. There are several neutral points appeared in the state of tension-compression equilibrium along the length direction of the anchor body,near which the rock mass on the elasto-plastic interface has significant rheological properties. Brittle fracture occurs while the maximum deviatoric stress from tangential to radial acted on the interfacial rock mass exceeds its long-term strength;② Pre-stressed full-length anchor bolts have an important influence on the strength parameters of the surrounding rock,and the bearing character- istics of the surrounding rock can effectively be improved with the increase of anchor pre-stress. Furthermore,the zonal thickness of surrounding rock,the width and number of fractured zone as well as the occurrence moment of sur-roun- ding rock begin to fracture change with anchor pre-stress;③ Under the action of anchor pre-stress,the strength in- crease of surrounding rock has some inhibitory effect on the fracture of the rock mass near the surface of the deep bur- ied cavern. With the gradual increase of the anchor pre-stress,the first neutral point of the anchor body is gradually moving to the surface of the cavern wall and the range of the first fracture zone gradually decreases until it reaches to zero;and finally ④ the rationality of the above conclusions is verified by a case study.