Mechanism and control technology of supports crushing induced by main roof’s breaking ahead of workface when crossing abandoned roadway

It has a safety significance to investigate the advance fracture of main roof and support crushing mechanism when workface crossing abandoned roadway or accessing to removal gateway. Similar simulation experiment was used to study the breaking characteristic of overlying strata,the stress on the surrounding rock and the load on the supports. Result shows that in the similar simulation of Shenhua Coal Mine,when the workface passing though the 12 m-wide roadway,the main roof was broken ahead of workface. Worse yet,the inferior key strata was broken at once and slid soon afterwards. The load exerted on the support increased from 4 000 kN to 12 500 kN then to 16 200 kN. The abutment pressure increased and moved forward. Impact of ahead distance,surrounding rock conditions and mining tech- nology on the stability of main roof was studied by mechanical model. Result shows that with the increase of ahead dis- tance,the working resistance increased sharply,with the increase of the height of free space or blockness,the stability of main roof structure decreased. The break of inferior key strata also leaded to working resistance increase sharply. It is better to prevent the advance fracture than increase the working resistance when it comes to maintaining the main roof’s stability in a similar workface. Above all,the control technology was put forward and the effect of site applica- tion was obvious.