Study On Deformation And Failure Law And Control Technology Of Surrounding Rock In Single Retracement Roadway

The pre-excavation retracement roadway is severely affected by mining in the final mining stage of fully mechanized working face,which is easy to cause large deformation of the surrounding rock of the retracement roadway and lead to accidents such as frame crushing and roof falling,which seriously restricts the retracement efficiency of the working face.In this paper,theoretical analysis,numerical simulation and field monitoring are combined to study the stress distribution of surrounding rock and the deformation characteristics of roof under the influence of mining in the pre-excavation single retracement roadway.The deformation and failure law of surrounding rock in the single retracement roadway is obtained,and the forced roof caving control technology is proposed based on the fracture mechanics theory.The main research contents and conclusions are as follows:(1)When the distance between the retracement roadway and the working face is far from each other,the mechanical models of the basic roof are established for the retracement roadway and the working face based on the elastic foundation beam theory.The formula of roof settlement ?(x)is derived,and the deformation law,internal force distribution and stress state of the surrounding rock of the basic roof rock beam are analyzed.The effects of elastic modulus E,hanging length x0,working face roof control strength f1,foundation coefficient k,buried depth H and supporting force P on roof displacement and surrounding rock stress are analyzed.(2)Based on the spatial position between the retracement roadway and the working face,the stress field of the retracement roadway and the stress field of the working face are superimposed.After the relative distance between the retracement roadway and the working face is reduced to a certain value,the retracement roadway is affected by the mining of the working face.According to the stress field state of the retracement roadway after superposition,the disturbance process of the retracement roadway before penetration is divided into three stages beginning affected by mining,large affected by mining and severe affected by mining.Based on the theoretical calculation of the engineering geological parameters of N1114 working face,it is concluded that the starting distance of the retracement roadway is 78 m affected by mining,the distance affected by large mining is 48.3 m,and the distance affected by severe mining is 5.16 m.The relationship curve between the mid-span settlement of the retracement roadway and the advancing distance of the working face is given.The maximum settlement of the basic top of the retracement roadway is 101 mm after penetration,and the monitoring results of the S4 section are compared and analyzed,which effectively verifies the rationality of the model in this paper.(3)After the connection between the retracement roadway and the working face,according to the different fracture positions of the basic roof,there are three failure modes of the basic roof behind the support,above the retracement roadway and in front of the non-mining coal mass,and the stability of the retracement roadway under each failure mode is analyzed.The results show that the fracture of the main roof behind the retracement roadway is the most favorable for the retracement work,the fracture above the retracement roadway is the most unfavorable for the retracement of the support,and the fracture in front of the retracement roadway is the most unfavorable for the stability of the surrounding rock.(4)Based on the finite element MIDAS/GTS numerical simulation software,the calculation model of single retracement roadway affected by mining is established,and the process of retracement roadway affected by mining is analyzed.The analysis results are consistent with the theoretical calculation.(5)In order to ensure the stability of the retracement roadway and control the roof fracture of the retracement roadway behind the retracement roadway,based on the fracture mechanics theory,the forced caving fracture mechanics model of inclined cracks is established,and the expression of the basic roof hanging length is deduced.Combined with the actual engineering geological conditions,the sensitivity analysis of the model parameters is carried out.