Study Of Delayed Supporting And Synergistic Bearing Mechanism Of Cable Bolt Based On Pre-tensioned Stress Coordination

The deformation process of surrounding rock in deep roadway has shown obvious nonlinear mechanical characteristics,and it is wildly accepted roadway stability control is closely related to the supporting process and strength and stiffness of supporting systems.The coupling between the strength and the stiffness of the rock bolt and cable bolt supporting structure is interrelated while it is also meanful for cable bolts to be delayed installed due to its limitation of elongation.However,the different supporting time of cable will lead to the differences of strength,stiffness and the stress states in the whole supporting system.Furthermore,these differences will also affect the support effect and the reaction of supporting system in mining process.In order to explore a better supporting(rock and cable)coupling stress state and the reasonable support time of cable,the thesis pursues the research and draws the following conclusions:(1)This thesis has determined the reasonable range of the hole diameter of the bolt body body diameter by using the laboratory drawing experiment.And based on the experimental results,this thesis modifies the Cable element in FLAC with two different modification strategies,all of which have been realized in numerical models.(2)This thesis has confirmed the significant effect of prestress field in improving the stress state of surrounding rock and strengthening its mechanical parameters from different angles which are Mohr stress circle,elastic mechanics and Hoke-Brown strength criterion.Meanwhile,the orthogonal simulation program of prestress matching is designed and simulated by FLAC software.The simulation results reveals that the diffusion and value of compressive stress will increase differently with the climb of prestress while the tensile stress changing in the end of bolt has also been analyzed.(3)An new index of prestress matching,“average compressive stress in roof”(ACS),has been proposed.It reveals that maximum of tension and compressive stress in supporting stress field is mainly related to the prestress of cable bolt.And two typical mismatch range of prestress in supporting system while the ideal matching range has also been divided based on ACS.(4)The theoretical maximum value of the deformation of the surrounding rock is obtained under supporting and unsupporting condition,thus the significant effect of cable bolt fot the deformation control of roadway has been revealed.Meanwhile,based on the roadway deformation law under unsupporting condition and the load and deformation state of rock bolt along roadway,the different surrounding rock deformation section in drilling period has been determined.(5)Based on the different deformation section of surrounding rock,the thesis carried out 5 different delayed supporting comparison schemes of cable bolt.The load state and supporting effect in drilling period of these different schemes have been analyzed.(6)The new indexs of failure of cable bolt,minimum principal stress(8)4)9))and volumetric strain rate(VSR)of surrounding rock,have been proposed by using the modified Cable element.It has been revealed that caused by the diffenences of supporting time and load state in drilling period,the cable failure time of different schemes in mining period is obviousely diffenent.And the delay of cable bolt may affect the primary supporting stress in mining period.The thesis consider the reasonable supporting time of cable bolt should be somewhere near the stable deformation section in roadway and certain coupling stress state which is incrising the rock bolt load in drilling period and giving more play to the supporting role of cable bolt in mining period.So a validation method of cable bolt supporting time has been proposed.(7)Aimed at some problems in 62 mining area of Wangzhuang coal mine like huge deformation and cable failure in roadway.Engineering experiment had been carried out in 6208 roadway in this mine.Support parameters,prestress and cable supporting time have been improved.And monitoring results reveals that supporting system stay in ideal coupling load state which didn't show the failure phenomenon and the deformation has also been well controlled,thus safe and normal service of the roadway has been ensured.