Study On Evolution Laws And Supporting Technology Of Zonal Disintegration Of Surrounding Rock In Deep Underground Cave

With the rapid development of the world economy,the development and utilization of deep rock mass engineering has become one of the hottest research directions in the domain of civil engineering.A large number of large deep rock engineerings such as mine roadways,diversion tunnels and oil war preparation storage projects that are more than a thousand meters deep were built.However,the excavation of the deep underground rock mass engineering exists a phenomenon different from the surrounding rock damage of the shallow cave,that is the phenomenon of zonal disintegration.It is great practical significance to study the zonal disintegration in deep rock mass because the deep rock mass engineering is the main trend of underground engineering in the future.Based on the previous research results,this paper took the fully grouted rockbolt under the condition of zonal disintegration as the research object.The evolution law of the zonal disintegration was analyzed through the systematic analysis of the stress characteristics of the bolt.The targeted surrounding rock support scheme was proposed.The main conclusions are as follows:(1)The formation process of zonal disintegration under deep buried condition was analyzed.At the initial stage after deep cave excavation,the surrounding rock stress is distributed and the first fractured zone formed.And then the stress is released and redistributed again.At this time,the outer boundary of the fractured zone is equivalent to the new excavation boundary.If the tangential peak supporting pressure of the redistribution is greater than the ultimate strength of the rock mass at the elastoplastic interface,second fractured zone will be formed.This situation will repeat until the fracture stops.(2)The force characteristics of the fully grouted bolt under the condition of zonal disintegration were analyzed.The stress of the surrounding rock will redistribute several times to form zonal distegration after the excavation.In this process,the surface frictional resistance of the same section of the bolt is different at different times.The surface frictional distribution of the different sections is different at the same time,which is characterized by the stress of the bolt being subjected to the alternating tension-pressure.Based on the principle of surrounding rock-bolt coordination deformation,the analysis model of bolt force under the condition of zonal disintegration was established.(3)The formula for determining the appeared moment of each fractured zone was proposed.The rheological characteristic of the rock mass at the elastoplastic interface is the key factor for zonal disintegration.Combined with the rheological property of rock mass at the elastoplastic interface and the theory of maximum deviatoric stress strength,the formula of the fractured moment of the rock mass at the elastoplastic interface of each zone were derived.The results show that the fractured moment of the rock mass is closely related to the mechanical properties of the rock mass,the maximum deviatoric stress and radial stress.(4)The formulas of the zonal thickness,fractured zone and the non-fractured zone in zonal disintegration were derived.According to the displacement characteristics between the bolt and the rock mass at the neutral point,The formula for calculating the neutral position of the bolt was derived.Based on the determination of the neutral point of the bolt,the theory of the neutral point and the elastoplastic deformation theory of the surrounding rock were used to derive the formula for calculating the zonal thickness,thickness of the fractured zone and the non-fractured zone.The results show that the relative outer diameter of the fractured zone decreases with the increase of the cohesive force and internal friction angle of the rock mass,and increases sharply with the increase of the excavation radius.Its thickness decreases rapidly with the increase of rock mass cohesion and internal friction angle.(5)A targeted surrounding rock support scheme under the condition of zonal disintegration was proposed.On the basis of the range of zonal disintegration area,fractured time and fractured zone thickness have been determined,the length of bolt and the grouting volume for each fractured zone were caculated.The bolt-grouting combined support scheme can determine the position,time and grouting volume in the process of supporting design.This support scheme provides a new idea for the support design of deep buried rock engineering.