North China Coalfields Research Articles

Impact of particle transfer on flow properties of crushed mudstones

Karst collapse pillar (KCP) is widespread in North China coalfields, where coal extraction above the Ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure. KCP is composed of rock skeleton and fine fillings, which can be transferred under the effect of water flow, thus KCP usually functions as a channel for groundwater inrush. In order to investigate the mechanism of mining-induced groundwater inrush of KCP which was caused by fine fillings transfer, a self-designed particle transfer permeability testing system was used to test the crushed mudstones’ flow properties, which included fine filling particle transfer rate, porosity increase rate and permeability under the conditions of varying pore pressure, particle size mixture and compaction level (initial porosity). The tests indicate fine fillings transfer is the essential reason for mining-induced groundwater inrush (flow instability) of KCP. The flow properties changeability during fine particle transfer could be divided into four stages, i.e., initial flow stage, flow inrush stage, continued particle flow stage and stable flow stage, and flow inrush stage which is the key point to cause water inrush. Due to the crushing of edges and corners and the adjustment of the structure, the fluctuation of permeability–time relationship mainly distributed in the first two stages, which make a change to flow channel. Moreover, with the increasing of pore pressure, particle size mixture and initial porosity, the water inrush time and stable seepage time decreased more rapidly; the fine fillings, porosity and permeability increased gradually. The efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well, and not all of the pore structures were in flow; this means there was a part of pores that were invalid, but the effective porosity in flow can be treated as calculation value approximately.

Development Law and Watery Features of Collapse Column in Pansan Mine

The collapse column is widely developed and distributed in North China coalfield, has been a threat for coal mine production safety. According to the existing collapse columns in pansan mine, using the combination with geology analyzing and geophysical exploration technology, the cause and development regularity of the collapse columns is discussed in a way of palaeogeographic and palaeoenvironment, the inner filling material features of the collapse columns in the coalfield are introduced, The watery features of collapse columns are studied. The results show that collapse columns have a law of zonation in the horizontal and vertical , and have a certain subsiding distance, collapse column widths ranging periphery have the peripheral edge of the impact zone and transition zone, In the collapse column, the cementation degree is poor at the top, highly compressed at the middle and relatively poor in the bottom. The top and middle sections are less in water bearing, the rich water in the bottom was caused by the vertically leakage recharge from Ordovician limestone in the deep. The research results provide scientific basis for the prevention of collapse column in coal mine.

Division Features of Coal-Bearing Tectonic Units in North China

Based on the new round of national potential evaluation on coal resources, and reference to the latest achievements about regional geological and energy basins, this article analyzed the main features of North China coalfield structure. According to the main features of North China coalfield structure and the distribution of North China coal series, the boundary of North China coal-bearing tectonic region and the division of North China coal-bearing tectonic units were identified. North China coalfield tectonic region can be divided into 5 coal-bearing tectonic sub-regions and 22 coal-bearing tectonic zones. The basic characteristics of the tectonic structure and its influence upon coal series distribution in each coal-bearing tectonic zone were systemically discussed.

Reseach on Controlling of Rock Mass Structure on Water Inrush From Coal Seam Floor in Huaibei Mining Area

Abstract Huaibei Mining Area is located in the south of the North China Coal-bearing Region. Its hydrogeological condition has basic features of the North China Coalfield. The hydrogeological condition is complex. The mining in the coal seam of Shanxi Formation where water inrush from coal seam floor happened mang times is generally seriously threatened by the limestone water from floor. The paper systematically analyzes typical cases about water inrush from coal seam floor in the researched area, and uncovered the different features of water inrush caused by different geological structure condition and water-inrush passage, which is of typical meaning to study controlling of rock mass structure on water inrush from coal seam floor.