Similar simulation experiments were carried out to study the chock sudden closure incident of hydraulic supports when the workface crossed the abandoned roadway or accessed to the removal roadway. The failure characteristics of surrounding rock

the abutment pressure and the working resistance of supports were investigated through the experiments

respectively. Results indicate that the advance fracture appeares before the incident when the workface crosses a large section roadway. The advance fracture leads to an increase of the block length

comparing to that in a normal periodic weighting. Meanwhile

the inferior key stratum brokes and then slides down to the main roof. Once the advance fracture occurrs

conventional supports are unable to prevent the block sliding

which indicates that an incident takes place. Therefore

the most important thing is to prevent the occurrence of advance fracture. To investigate the main causes for the advance fracture

bending moment and deflection of the main roof are calculated by the Winkler foundation beam theory. The calculated results comprehensively explain the failure characteristics of surrounding rock

the abutment pressure and the working resistance of supports. Finally

it is revealed that the failure of coal pillar is the reason for advance fracture of the main roof. Hence

it is significant to improve the strength of coal pillar. At last

a roadway filling strategy is put forward to make uniaxial compression of coal pillar into triaxial compression by Shenghua coal mine. In-situ tests verifies that the strength of coal pillar is successfully increased.