Study On The Zonal Disintegration Law Of Deep Rock Mass And Support Optimization Under The Action Of Prestressed Anchoring Bolt

In recent years,people's demand for deep underground resources and space has been increasing,and a large number of deep rock engineering have appeared.Because the deep rock mass engineering is in the complex mechanical environment of "three highs and one disturbance",the surrounding rock is prone to many engineering disasters such as zonal disintegration,rock burst and large deformation of extrusion.On the one hand,at the beginning of the excavation of the cave,it is necessary to support the deep buried surrounding rocks with bolts;on the other hand,the zonal disintegration of the surrounding rocks has a significant time effect.There fore,the occurrence and development process of the surrounding rocks zonal disintegration in engineering practice is essentially the result of the coupling action by bolt and rock.Based on the summary analysis of the research results about domestic and foreign surrounding rock on zonal disintegration.This paper takes the surrounding rock of deep buried after support of pre-stressed anchor body as the research object.Through systematic analysis of the stress characteristics of prestressed anchors under the condition of zonal disintegration,inverse analysis of the evolution law of the surrounding rock zonal of deep buried caves under different prestresses was carried out.And a support optimized design scheme for the surrounding rock of zonal disintegration is proposed.The main conclusions are as follows:(1)The mechanical criterion for the zonal disintegration rock fracture under the pre-stressed of anchor bolts is established.Considering the anchoring effect of pre-stressed anchoring bolts,based on the Griffith strength theory,radial tensile cracking failure occurs when the tensile strain of the rock mass at the elastoplastic boundary under the action of tangential compressive stress reaches the ultimate tensile strain.By analyzing the influence of different reaction force under pallets on the surrounding rocks strength parameters of the cave.The distribution law of the surrounding rocks stress in the cave before and after the pre-stressed bolt support is studied,and the influence mechanism of the bolts pre-stress on the surrounding rocks strength is revealed.(2)The distribution rule of the neutral points of the anchor rod along its length under the condition of zonal disintegration is analyzed.Based on the principle of coordinated deformation between pre-stressed anchor bolts and surrounding rocks,a mechanical model of the interaction between prestressed anchors and surrounding rock under the condition of zonal disintegration is constructed.According to the characteristic that the relative displacement between the surrounding rocks and the rod body is zero,the non-unique solution of the neutral point position of the rod body when zonal disintegration of surrounding rocks is derived.It provides a basis for determining the theoretical value of the position of the neutral point of the prestressed anchor bolts under the fracture condition of the surrounding rocks.(3)The effect of bolts prestressed on the spatial distribution of zonal disintegration of surrounding rocks is discussed.Based on the anchor neutral point theory,The multi-solution inversion of the neutral position of the rod body is used to analyze the thickness of any surrounding rocks zone,plastic zone and fracture zone under different pre-stress conditions.The basic influence law of pre-stress on the spatial distribution of fractured surrounding rock is obtained.The results show that with the gradual increase of the prestress of the anchor rod,the neutral point of the anchor rod gradually moves towards the cave wall,and the thickness of the crack zone of the cave wall decreases rapidly;the range of the crack zone of the cave wall decreases with the increase of the anchor rod density.(4)The effect of anchor prestress on the spatial distribution of the zonal disintegration of surrounding rock is discussed.The rock mass has obvious rheological properties on the elastoplastic interface of deep buried caverns.When the maximum deviatoric stress between the tangential and radial directions exceeds its long-term strength,brittle tensile cracking occurs.According to the nonlinear rheological model of the rock mass at the elastoplastic interface of the surrounding rock and the maximum deviatoric stress in the tangential and radial directions,the theoretical formula for calculating the moment of occurrence of the zone break is established.The analysis of the example shows that the occurrence of the cracking zone of the cave wall is advanced with the increase of the prestress.(5)An optimization scheme for the support of zonal disintegration in deep-buried caves is proposed.Based on the study of the effect of surrounding rock rupture time,location,thickness and number of rupture zones,the prestress,length,row spacing and grouting volume of bolts under zonal disintegration were optimized,and the best time for secondary support was proposed.Through the use of hollow section spiral grouting anchor bolts,the surrounding rocks in each fractured area was grouted in stages,and the optimized support for partitioned fractured surrounding rocks were achieved in terms of grouting time,grouting position and strength recovery.