Study On Failure-Reconstruction Mechanism Of Surrounding Rock Bearing Structure Of Soft Rock Roadway

The support problem of soft roadway has always affected the safe and efficient production of coal mine.The surrounding rock of 2154 floor roadway in Puxi Well of Jiahe Mine belongs to low strength siltstone and sandy mudstone.The roof and floor have large deformation,and the damage of the two sides is serious,and the support problem is particularly prominent.To study its stability,the paper takes the roadway as the research background and relies on the General project of National Natural Science Foundation of China(52074115).Field test,experimental research,theoretical analysis and numerical simulation are adopted.This paper systematically studied the failure characteristics of soft rock roadway after confining peak,the reconstruction characteristics of anchor carrier and the stability control technology of surrounding rock,and applied the research results to the engineering practice of soft rock roadway,and achieved good results.The main conclusions are as follows:(1)Through the analysis of in-situ stress test results of test roadway in Jiahe mine,it is found that the in-situ stress field is mainly horizontal stress field.The average inclination Angle of the maximum and minimum horizontal principal stresses is 10.6°,almost close to the horizontal direction,and they are basically vertical in orientation.The average inclination Angle of vertical principal stress is 65.9°,close to the vertical direction.There are a lot of kaolinite minerals(9.52%)in the surrounding rock,which are soillike or massive,with low hardness,easy to soften after water,which can greatly reduce the strength of the surrounding rock.(2)Uniaxial compression test,conventional triaxial compression test and pre-peak unloading confining pressure test were carried out on sandstone specimens by testing machine.At the loading rate of 0.1k N/s,the average elastic modulus and uniaxial compressive strength of sandstone in 2154 floor roadway are 6.93 GPa and 34.8 MPa respectively.Under uniaxial compression,the failure mode presents an "X" type,and when confining pressure is applied,a single inclined plane shear failure occurs.Under the condition of low confining pressure,it shows the characteristics of brittle softening,and with the increase of confining pressure,it gradually transforms from brittle softening to ductile state,which is reflected in the stressstrain curve,which gradually transforms from near-vertical to horizontal.After unloading,the growth of circumferential strain is significantly greater than that of axial strain,showing the characteristics of volume dilatation,indicating that unloading plays a leading role in the growth of specimen volume.(3)A large proportion three-dimensionnal similar simulation test rig that can simulate real three-dimensionnal stress is developed.The complete specimen is precracked by a front reaction frame,and bolts with different support densities can be installed on the precracked specimen.With the increase of the supporting density of bolt,the bearing capacity of the broken specimen increases gradually.The fractal dimension of fracture and fracture increases exponentially with the increase of bolt support density.The deformation amount of roadway surrounding rock has the same variation trend with the fractal dimension of surrounding rock breakage,and the larger the fractal dimension is,the larger the deformation amount of surrounding rock is.The fractal dimension of roadway surrounding rock fissure can be used as an index to evaluate the stability of roadway roof.Bolting resistance increase the probability of has broken surrounding rock broken again,make further broke into fragment size pieces of level,make the fragment gradation distribution closer to the optimal gradation with the lowest void ratio of surrounding rock in plastic zone.In other words,the effect of bolt is to fracture probability,by increasing the fragments of fractal dimension of fracture fragments to reduce crushing roadway space eroded volume expansion process.The fractal dimension increases with the bolt support density,and there is a positive correlation between bolt support density and fractal dimension.(4)Through field observation and numerical simulation,it is found that the bolt support has little effect on changing the stress distribution law of the original rock and can not inhibit the expansion of the plastic zone,but the support resistance provided by the bolt support plays an important role in the additional stress field provided by the broken surrounding rock and the bearing capacity of the broken surrounding rock.The length of anchor rod plays a decisive role in the performance of anchor material.The anchor foundation should be in a stable elastic zone outside the plastic zone to ensure that the failure mode of anchor bolt is the ideal tensile failure mode.Reasonable preloading force applied by bolt is the key to give full play to the material properties of bolt,reduce the length of bolt and form a stable anchor bearing structure.The greater the preloading force is,the greater the compressive stress value formed in surrounding rock is,and the greater the compressive stress area is,which can significantly improve the active support function of bolt.Increasing the bolt pretightening force is equivalent to exerting a certain confining pressure on the broken surrounding rock in the plastic zone.Although the expansion of the plastic zone cannot be suppressed,the bolt support has a certain effect on limiting the development of the plastic zone,which can reduce the expansion rate of the plastic zone and the number of repairing tunnels to a certain extent.(5)based on the butterfly of surrounding rock mass of roadway destruction theory,put forward "local reinforcement,whole section coordinate deformation of the supporting ideas,design a new base of 2154 lane support scheme,from the numerical simulation model of the effect of the simulation results and field test section,the anchor rope support mining companies have effective control golden Pu Xi Wells of floor roadway deformation.That the deformation of surrounding rock can be effectively reduced by adopting the new support scheme was found,without the phenomenon of anchoring failure,and the deformation of surrounding rock meets the requirements of mine safety production during the monitoring period.