FAILURE CHARACTERISTIC AND FRACTURE EVOLUTION LAW OF OVERBURDEN OF THICK COAL IN FULLY MECHANIZED SUB-LEVEL CAVING MINING

In mining process, the height of water flowing fractured zone is significance in preventing mine water and gas. This paper further researchs the failure characteristic of the overlying strata. It takes certain coalmine with 5.82m mining height as the experimental face. It uses water injection and televiewer methods in drillholes, ground penetrating radar, and microseismic monitoring system in underground coalmine. It monitors the height of water flowing fractured zone of fully-mechanized top caving. It conducts numerical simulation experiment on the failure process and similarity simulation experiment on the cracks evolution at the same time. It modifies the empirical formula. The results show that:The heights of caving and fractured zones are respectively 43.1m and 86.7m in fully mechanized sub-level caving mining. The data difference of each test method of caving zone, fractured zone and water flowing fractured zone is respectively less than 4.5%, 7.1%, and 9.0%.The degree of fracture development is low before mining. The number of fissures is obviously increased after mining. The degree of fracture development is increased. The fracture cluster region mainly focuses near the coal wall. The fracture density distribution curves of overlying strata like sanke-shapes. The new empirical formula of water flowing fractured zone height is proposed and can adapt to certain coalmine geological conditions.