Cutting block structure model of overburden with shallow buried coal seam and ultra-large mining height working face

Based on the data of shallow buried workface measured at 30 working faces in seven collieries,the charac- teristics of ground pressure of workface were obtained,i. e. the intensive pressure phenomenon in workface is more se- rious than that in entries,the periodical pressure step is relatively shorter,the dynamic load coefficient is larger,the curve of hydraulic support resistance is monotonic rising and falling,the collapse of overburden strata extends to sur- face directly,the maximum subsidence of the distance to roof 26 m is 227 mm after the workface advancement 11 m, the maximum subsidence of surface is 5. 89 m after the workface advancement 296 m,which is quite different from normal geotechnical condition that the ground pressure of workface is proportional to the depth of coal seams. Several observations and measurements about ground pressure were carried out in the super-high 12401 mining workface with 8. 8 m mining height in Shangwan colliery. A new model which described the broken structure of overburden in work- face was proposed as a “cutting block” model which could explain the reasons why hydraulic supports were often pres- sured into end-limited status in shallow buried geotechnical condition and obvious terraces were easily found on the surface where workface was below. In order to understand well for this new model,some physical simulations were built based on the 12401 workface practical strata in the experiment laboratory. A formula to calculate hydraulic powered supports working resistance was also derived from this model. The results were finally proved in Shangwan colliery.