Study On The Control Technology Of Surrounding Rock With High Pretension Bolt & Cable In Jianxin Coal Mine

The design of a reasonable bolt&cable preload can give full play to the performance of the support material and improve the stiffness and stability of the support system,however,the design often takes 0.3～0.5 of the breaking load as the design value of the preload,without considering various factors such as the anchoring effect of the coal rock body,bolt&cable preload matching,preload stress transformation and preload stress loss.In fact,the anchoring effect of the coal rock body is generally poor,and the anchor agent interface is often damaged before the anchor rod and cable body.This thesis focuses on the working face of the 42 pan area of Jianxin coal mine,and carries out research on the control technology of high preload stress anchor ropes around the coal rock in Jianxin coal mine.The main findings of the study are as follows:(1)The critical anchorage length,preload stress conversion factor and loss rate of bolt&cable were determined in field tests.The practice showed that the pull-out force of the bolt&cable at the critical anchorage length was significantly different from their breaking load and that the coal rock was poorly anchorable.Using FLAC3 D numerical simulation to simulate the stress distribution in the surrounding rock under nine preload stress scenarios,it was determined that the diffusion of compressive stress in the surrounding rock is best when the difference between bolt preload and cable preload is large(bolt preload 42 k N to 56 k N and cable preload 144 k N to 180 k N).(2)Four high-stiffness preload stress matching schemes were designed,and the Burgers intrinsic model was used to carry out roadway creep simulation and workface retrieval simulation using FLAC3 D,respectively,to analyse the surface deformation time-varying curves,roadway perimeter rock deformation clouds and perimeter rock body vertical stresses under different matching schemes,concluding that the magnitude of cable preload is the core of the stiffness of the preload bearing structure,and the response of the cable pre-stress is more sensitive than the bolt pre-stress;the control effect of the bolt pre-stress on the deformation of the surrounding rock of the roadway during the recovery period is further reduced;the control effect of the surrounding rock is significantly improved in options 3 and 4 compared with options 1 and 2,forming a more effective pre-stress support structure.(3)Industrial tests were carried out in different sections of the working face in the42 plate area of Jianxin coal mine.Through the analysis of mine pressure data,when the cable tension is 300 k N and the bolt preload torque is 360N·m,i.e.Option 3 has the best control effect on the surrounding rock of the roadway,which can effectively reduce the degree of surrounding rock deformation and maintain the stability of the roadway,and is the best option for the preload stress of the high preload stress bolt&cable in Jianxin coal mine.It is further verified that the bolt preload and cable preload differential is larger and the cable preload level is higher,which is more beneficial to the control of the surrounding rock of the roadway.There are 54 figures,12 tables and 90 references.