Fracture evolution and failure characteristics of roadway surrounding rock in extra-thick coal seams subjected to multiple coal bursts
Focusing on the large deformation and roof collapse generally occured for under-ground roadway in extra-thick coal seam affected by the multiple coal burst,both the fracture evolution and damage characteristics of the surrounding rock was investigated upon the de-struction mechanism of surrounding rock and dynamic theory for coal burst.In the present re-search,the elasto-plastic theoretical damage model with the consideration of multiple impact disturbances was initially established and the dynamic evolution law either in terms of the elas-tic-plastic zone or the damage zone of the surrounding rock under the combined dynamic and static loads were elucidated.Subsequently,the maximum range of the loose destruction zone of surrounding rock was calculated upon the given coal mine.The theoretical equations of elastic-ity,plasticity and crushing zone were then derived,suggesting that both the range of crushing zone and plastic zone were positively correlated with the radius of the roadway,the pressure of overburden and the intensity of the impact and vibration,whereas the value of which are nega-tively correlated with the strength of the peripheral support.In particular,the influence of the roadway radius is much more significant on the range of peripheral rock looseness zone.The e-volution and destruction characteristics of the fissures within the peripheral rock was indicated that the derivation of tensile fissures is an important reason for the development of shallow crushed zone,while the expansion of shear slip fissures plays the dominant role in the develop-ment of deep plastic zone.The damage and control mechanism of the roadway in this case was also clarified,which demonstrated that a large number of cracks originally developed in the loose and brittle coal seam,when the shock wave is transmitted to the roadway.These cracks expanded quickly and the fracture zones intersect and penetrate each other,which instantly caused structural damage and affect the load bearing stability of surrounding rock.Upon the calculated range of damage area and plastic zone,the technique route for the roadway support featured with the technology of"hard top pre-cracking+coal body double unloading+anchor network strong support"was proposed and put into practice.It is believed that the main find-ings obtained from this research provide a new insight and meaningful reference to maintain the stability of surrounding rock subjected to multiple coal bursts.
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