Mechanism Of Deformation And Failure In Large Chamber Group Of Soft Rock Underpass Layer And Its Control Countermeasures

The blind shaft chamber group of Maoping Mine is an important passage to the deep part of the mine.Due to the large design section of the chamber and the close interaction of the chamber group,the stress environment is complex.Under the action of high ground stress,the surrounding rock of the chamber group undergoes differential rheological deformation and failure of the original support structure,which seriously affects the production and operation of the mine.Through the methods of field investigation,theoretical analysis and numerical simulation,the stress and displacement evolution laws of the chamber group under the excavation process and the original support condition are analyzed.The rheological deformation and failure characteristics of the surrounding rock of the chamber group are revealed.The deformation and failure mechanism of surrounding rock and the main control factors affecting the stability of chamber group are analyzed.The soft rock deformation mechanics mechanism and targeted control measures of the surrounding rock of the chamber group are analyzed.The reinforcement and support effect of chamber group is simulated and monitored on site.The main conclusions are as follows :(1)Through field investigation,the engineering geological conditions of the chamber group are analyzed.The overall structure of the chamber group is complex,the adjacent tunnels and chamber are interconnected,and the chamber group is located at the junction of soft rock and hard rock strata.The regional geological structure of the chamber group is relatively complex,and the tectonic stress is large.The local stress concentration of the surrounding rock of the chamber is high.The joint fissures of the surrounding rock are developed,and the rock strength is low.The surrounding rock of the soft rock chamber is mainly loose and broken soft rock containing expansive clay minerals.(2)Through the analysis of the original support mode of the chamber group and the characteristics of differential deformation and failure of surrounding rock,it is concluded that the main reason for the deformation and instability of the chamber group is that the asymmetry of the rock structure and the chamber group structure leads to the uneven distribution of the stress field of the surrounding rock of the chamber group,the strength of the original support structure is low,and the surrounding rock undergoes large rheological deformation under the action of high stress,while the original support structure is not coupled with the large deformation of the surrounding rock,resulting in serious deformation and failure of the surrounding rock of the soft rock chamber.The excavation process of the chamber group and the rheological deformation and failure process of the surrounding rock are simulated by using the numerical simulation method.The evolution of the maximum principal stress and the displacement change of the surrounding rock are analyzed.Combined with the analysis of the characteristics and mechanism of the deformation and failure of the surrounding rock,it is concluded that the main factors affecting the stability of the chamber group are high ground stress,local stress concentration,low strength of surrounding rock,large rheological deformation of soft rock and groundwater seepage erosion.(3)Through the theoretical analysis of soft rock engineering mechanics,it is determined that the soft rock type of chamber group is high stress jointed expansive composite soft rock,which has IAIIACDIIIE type,namely molecular water absorption expansion type,tectonic stress,water action and engineering deviatoric stress type and random joint type composite deformation mechanics mechanism,and puts forward corresponding control countermeasures.The composite deformation mechanics mechanism is transformed into a single type to control the rheological deformation of surrounding rock.(4)Through the simulation analysis of the stability control effect of chamber group,the surrounding rock control scheme of the chamber group can effectively control the rheological deformation of the surrounding rock,change the tensile stress of the surrounding rock of the chamber to the distribution state of the compressive stress,reduce the range of the plastic failure zone of the surrounding rock,and verify the feasibility of the support and reinforcement scheme.(5)In view of the different deformation and failure characteristics of chambers,deep and shallow hole grouting,multi-level and different levels of prestressed anchor cable and steel plate combined reinforcement and chain anchor beam anti-bottom arch targeted reinforcement support scheme are adopted.The field monitoring of the reinforcement support effect shows that the deformation rate of the surrounding rock after the reinforcement of the chamber becomes smaller and gradually converges,and the anchorage state of the anchor cable is stable.The surrounding rock control scheme of the chamber group can effectively control the rheological deformation of the surrounding rock and ensure the long-term stability of the chamber group.