The Research Of Mechanical Behavior On Surrounding Rock Of Roadways Based On Non-pillar Sublevel Caving With Large Drive Interval And High Sublevel

The non-pillar sublevel caving is one of the most important mining methods for many metal mines in China.With the development of ore-drawing theory and trackless mining equipment,the mining structure parameter has been being increased in recent years.However,the studies on deformation,failure mechanism of roadway are not thorough enough.Therefore,based on non-pillar caving with high sublevel and large drive interval,the research contents of this paper are focused on mechanical behaviors of surrounding rock of roadway.Such studies are of great theoretical and practical significance on security evaluation,reasonable supporting,geostatic management,and so on.The main study work and conclusions are as follows:(1)Based on characteristics of mining method,a mechanical model for roadway with arbitrary shapes is established by means of complex function,and the elastic mechanical behaviors of three-centered arch are discussed in detail:Under one-way vertical load,the bottom corner and small arch region of roadway are two main stress concentration regions,the stress concentration factors of which are 3.5?8 and 1.5?3.The large arch region is mainly in tension state and its concentration factor is-1?1.5.The concentration factors of side walls and floor region are relatively stable,which are about 2 and-1 respectively.Therefore,the curvature of bottom corner and small arch region shouldn't be too large for preventing serious compressional deformation caused by stress concentration.The strict linear relation is found between stress concentration factor and lateral pressure coefficient.The curve of stress concentration factor under arbitrary lateral pressure coefficient can be obtained by grasping its growth rate curve only related to the geometrical shape of the roadway.According to mechanical analysis on surrounding rock of roadway,the influence range for side walls should be seriously considered as design roadway spacing,the influence range for both bottom corner and arch region should be seriously considered as design sublevel height.(2)The three-dimensional finite difference models for roadway group are established based on non-pillar caving method,which are mainly for analyzing the mechanical behavior of roadway group before and after mining.The calculation results before mining show that stress distribution law of roadway boundary is consistent with the analytical solution.The larger the structural parameters,the higher the maximum principal stress concentration in the large arch and floor region,and lower in the side walls.For same structural parameter,the stress concentration factor will increase with increase of sublevel depth.Therefore,it is not advisable to excavate the third or fourth sublevel in advance under limited productive efficiency.The stress field of the roadway group shows the periodic characteristics,and the variation law within periodic step keeps high consistency with analytical solution under large structural parameter.However the vertical stress in the central region of the pillar is enhanced and the horizontal stress is attenuated under small structural parameters,which easily lead to the instability of the pillar.The mining simulation shows that stress field of roadway can be divided into three regions which include stress unloading,stress bearing,and stress stability region.Therefore,the stagger distance between two adjacent roadways in different sublevel should be larger than the range of stress bearing region,which ensure the floor stability of the upper section.The mining stagger distance between two adjacent roadways in the same sublevel shouldn't be too large,which will easily cause compression and shear damage on the side walls of adjacent roadway.The interaction effect between structural parameter and stagger distance shows the stress of surrounding rock with small structural parameter is more sensitive to stagger distance than large structural parameter.Therefore,the large structure parameter is more favorable for the stability of surrounding rock in mining process.(3)The coupled continuum-discrete simulation and moment tensor algorithm are utilized to discuss the deformation and failure mechanism of surrounding rock,and the distribution characteristics of moment magnitude.With increase of one-way vertical load,the local breakage emerges nearby stress concentration zones including arch springing and bottom corner regions,and the tension crack emerges in the roof of roadway.Thereafter,the "V" type breakage zones are shaped in the two side walls under cutting action of initial cracks.As confining pressure is in low level,the failure extent is restrained,but the failure mode is not changed and more explosive events will be generated.With increase of confining pressure,the "V" type breakage zones will be disappeared,the more implosive and pure shear events will be generated,and the compression-shear damage emerges in roof and floor.As the lateral pressure coefficient is greater than 1,the "V" type zonal disintegration of floor and roof will be serious,and implosive event be in dominant position.With the increase of damage of surrounding rock,the crack zones are generated along damage boundary,which easily cause roof caving,and spilt failure of two side walls within the damage area.As the damage is very serious,the surrounding rock within damage region will produce large-area collapse.The events of high moment magnitude are normally distributed along the crack band that is well developed,while the moment magnitudes inside of rupture zone are often in low level.The moment magnitude also shows radiation law that the magnitude values in the core area of rupture source are often largest,and then decay gradually outwards.The larger the rupture scale of surrounding rock,the higher the occurrence probability of high moment magnitude.The large scale rupture often occurs in the final stage of the destruction of the surrounding rock,that is,when meso-scale rupture penetrates,the large-scale fracture slip occurs.(4)The monitor results show the force of mortar anchor can be divided into three phases with advance of working face,which are stabilization,pressure-bearing,and unloading stage.This corresponds to the three stress variation regions of the mining simulation,indicating that the distribution law is universal.Therefore,the support of surrounding rock with poor quality should be reinforced ahead of pressure-bearing stage,amount of segment charge should also be reduced or more segments are set up.