According to the results of mine pressure, the hydraulic acrow props load of the working face, the amount of roof subsidence, and the degree of roof fracture are all increasing from the coal wall to the old pond side. If the hydraulic acrow props controls the top distance, the longer the pillar bearing time, the longer the pressure The larger, the more broken the roof.
Since the introduction of wall coal mining, many coal mines have used steel acrow props, due to the large roof control distance, which often caused the props to skewed and deformed, the roof was broken, the gangue fell seriously, and the gangue and roof fell on the steel acrow props working face. By reducing the top control distance, the pressure of the working column is reduced, which increases the initial investment and preparation work of the working face.
When caving the roof in wall coal mining, when the direct roof is soft and broken, and can fall in time, the "three·four" control roof is adopted before and after the initial pressure. For the working face with suspended roof before the initial pressure, the acrow prop control distance should be increased, and the working face should have sufficient support strength to prevent the occurrence of push-down acrow prop fall accidents.
