Abstract
The thick Cenozoic unconsolidated aquifer is deposited under Sunan syncline core in Huaibei coalfield, the water yield property of unconsolidated bottom aquifer is strong and water pressure is high in some areas (up to 4 MPa in some areas). Water inrush accident often occurs during mining under unconsolidated aquifer, the biggest characteristic is abnormal mine pressure and support break-off during water inrush accident comparing with normal condition. In order to study mechanism of support break-off and water inrush during mining under the high confined thick unconsolidated aquifer, a simulation of similar material was designed. The experimental results indicated that, under normal condition, the compound breakage sequence of water-resisting key strata between coal seam and high confined thick unconsolidated aquifer is from top to bottom and the basic reason of synchronous fracture is the load of bottom key strata increased suddenly when the breakage of top key strata happened. Because of high confined thick unconsolidated aquifer, surface acts on the bottom key strata soil layer in the form of uniformly distributed load, which is the load-transfer mechanism of confined thick unconsolidated aquifer. Once the overlying key strata compound breaks, the height of unstable strata will reach far more than 30 meters and exceed support capability of current fully-mechanized mining supporter, which leads to support break-off accident during mining process under confined unconsolidated aquifer.
Highlights
Most of coalfield in North China are concealed coalfield covered by large-thick Cenozoic unconsolidated layers [1]
Coal-bearing strata are covered with Cenozoic unconsolidated layers which belong to concealed coalfield
The sequence of key strata break is the above key strata breaking off firstly, and load of the lower key strata suddenly increases in an instant of the above breaking, which is the basic reason of synchronous breaking with the above key strata
Summary
Most of coalfield in North China are concealed coalfield covered by large-thick Cenozoic unconsolidated layers [1]. The roof pressure increased periodically with the advance of working face which shows that this kind of accident is associated with hydrogeology characteristics of high confined unconsolidated aquifer and associated with structure types and the breakage characters of overburden strata [9]-[11]. Coal mining condition under high confined thick unconsolidated aquifer was modeled based on similar material simulation experiment. We obtained stress distribution law and roof displacement characteristics of surrounding rock strata, which provided technical support to further study of support break-off water inrush mechanism during mining under high confined thick unconsolidated aquifer
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