中埋深煤层综采地表裂缝发育规律研究

In order to reveal development law, spatial form, and depth characteristics of ground cracks induced by high-strength mining in the medium buried working face in Jurassic Coalfield in northern Shaanxi, with a first-mined working face of Xiaobaodang Coalmine in Jurassic Coalfield in northern Shaanxi as research area, static and dynamic evolution law and spatial distribution of ground cracks in high-strength coal seams mining in medium and deep coal seams in windy and sandy area were studies through ground cracks mapping, dynamic observation of the change of cracks width, and cracks tracing excavation observation. The results have shown that two kinds of ground cracks develop in working face 112201: boundary cracks and cracks within the working face. Specifically, boundary cracks develop along the trough and cut hole, while the latter develop paralleling to cut hole in the working face. The ground cracks with width less than 1.0 cm accounts for 73% and those larger than 5.0 cm accounts for 3%. Overall development of cracks is weak. Besides, the width of cracks within the working face is generally less than 2.0 cm and there is no drop on both sides. Dynamic cracks in the working face always develop behind current working location, with average lag distance of 30.14 m and lag angle of 84.1°. With advancement of working face, changes of the width of cracks within the working face present a unimodal type, i.e., cracks change dynamically by fracturing first and then closing/half closing. The process of dynamic crack takes 7.8 d averagely, and the time taken to increase of crack width is basically the same as that of decrease. On the basis of observation of surface movement, a function for the time of dynamic crack change was established. Boundary cracks parallel to groove, presenting a belt shape, are distributed in the range of 56 m from inner side and 18 m from the outside of the trough. The spatial characteristics of ground cracks within the working face were divided into three types: wedge shape, shuttle shape, and bifurcate shape. The development depth of cracks in the sand layer are less than 2.5 m. Generally, under the function of aeolian sand, ground cracks with a width less than 5 cm will be buried within two months, but for those with a width greater than 5cm, the time for cracks to be buried with aeolian sand is six months. The results of this study have important reference value for ecological environment control and water resources protection in the wind beach area.