Research on roof deformation laws and mechanism in a non-pillar mining method with entry automatically formed during the whole cycle

Non-pillar mining with entry automatically formed is a systematic process,and the retained entry must undergo the influence of excavation period,the advance mining of the working face,the overburden movement of the lagging working face and the advance mining of the next working face. Therefore,the study of roadway roof deformation should be considered in a full cycle. Taking coal mining in Shen Fu and Dongsheng coal mining areas as the engineering background,the roof deformation laws and mechanism in the process of gob-side entry by roof cutting were comprehensively studied by means of theoretical analysis,numerical simulation and field test. Under the conditions of thin bedrock layer and loose layer thickness in mining coal seam,thick loose layer can be simplified as overburden load,and the deformation of roadway roof can be regarded as the roof to control the deformation of key rock layer. The roof can be regarded as a statically indeterminate beam structure fixed at both ends during the roadway excavation. The roof can be regarded as a simple supported state with different stress states in the pre-split cutting stage,the road staying stabilization stage,and the secondary mining advance effect stage. The roof can be regarded as a cantilever state during the mining influence stage. Theoretical analysis shows that the most easily deformed position of roof is the free end of cantilever beam in the initial mining stage. This stage is the most unstable stage in the process of retaining roadway,and high-strength temporary support should be done well. Numerical simulation and field test indicate that the stress and displacement of roadway roof are the smallest and symmetrical distribution in the excavation stage,and the stress of roadway roof begins to appear asymmetrical distribution after presplitting cutting slots. In the initial mining stage,the stress of surrounding rock increases significantly and eventually tends to be stable. In the second mining stage,the stress of surrounding rock of roadway will increase again. Through numerical simulation and field test,it is found that the deformation of roadway roof corresponds to the stress distribution. The roof slightly deforms in the roadway excavation stage,and the displacement increment and speed-up are small in the presplitting and slotting stage.The influence stage of primary mining is the most severe stage of surrounding rock deformation. The increment of roof deformation is mainly concentrated in this stage,and then the roof tends to be stable. Secondary mining has little influence on the roof deformation of roadway.