Instability mechanism and deep hole grouting control technology of composite roof in fully-mechanized mining face

In order to solve the problem of roof and coal wall stability of fully-mechanized mining face with large mining height under complex geological conditions,the stability of coal wall in fully-mechanized mining face was analyzed by numerical simulation.Based on this,the deep hole grouting control technology of deep coal wall and composite roof giving priority to consider the gangue splitting and seepage grouting reinforcement of roof,and then permeation grouting for the coal was proposed,which was applied in the engineering successfully.The results showed that the control technology presented realizes the relatively comprehensive reinforcement for the deep coal wall and composite roof.The falling heights of roof of 200～300 mm for the roof occur in the test area and there is little coal wall spalling phenomenon，ensuring the stability of the roof and coal wall during the stoping process.Moreover,the grouting cost using superfine cement grouts is only 1/9 of the chemical grouts such as the flexurane,which has remarkable economic benefits.