UDEC simulation of the water-pouring probability in exploiting waterproof coal pillars under the conditions of thick loose bed and ultrathin overlying strata

It is gained that the height of falling zone of overlying strata in the middle of the coal face in a certain colliery which lies in the conditions of thick loose bed and ultrathin overlying strata increases and the height of fracture zone expands gradually with the increasing of caving ratio by UDEC simulation of four working conditions and physical simulation which is used to validate UDEC simulation of the destroyed characteristics of overlying strata."Three Zones" come into being along the height of overlying strata.However,the destroyed zones along uprightness are different from other exploiting technique.The height of fracture zone is close to that of falling zone in the middle of overlying rocks and the roof rocks subside entirely.The height of fracture zone can arrive at 20～22m high at most when the coal face is mined by the ratio of 2∶1 or 2.5∶1.By analyzing the destroy rule and the hydrological and geological characteristics of overlying strata,water bursting accidents will not happen in the period of exploiting.