Under the dual action of mining and topography, the development rules of mining fractures in loess gully are complex and the disaster forms are diverse in Shenfu mine area, which is a major problem restricting mine safety production and damaging ecological environment. Taking the typical loess hilly working face of Shenfu mine area as the engineering background, this paper adopts the methods of laboratory test, similarity simulation, numerical simulation, theoretical analysis and field monitoring to conduct comprehensive research, and reveal the development mechanism of loess hilly mining fractures, which provides a certain theoretical basis for resource development and disaster management in mining area. The main achievements of the paper are as follows:
(1)Based on slope occurrence and erosion degree, loess hilly were divided into three types : shallow gully, deep gully, and erosion gully. The variation of the composition, pore structure and physical index of the gully soil layer with the buried depth are analyzed through laboratory experiments. The results show that the proportion of viscous minerals in soil decreases, the large and medium overhead pore structure decreases, the loess particle compactness increases obviously. FLAC3D numerical simulation analysis shows that the original surface stress of loess hilly exists regional concentration, and the surface stress concentration is aggravated by the working face mining, which increases the movement range and amount of gully slope.
(2)The physical similarity models of loess hilly landforms in shallow gully, deep gully and erosive loess was established to analyze the development characteristics of mining fractures, the results showed that the mining fractures in gully bottom were mainly shear failure, and the fracture morphology was approximately “I”, and some cracks were closed by extrusion of slope; the reverse slope mining fracture is mainly caused by tensile failure, and the fracture shape is approximately “V” under the slope body weight; the downslope mining fracture is mainly tensile failure, while the fracture of slope body is mostly closed by rotary extrusion. At the same time, it is revealed that there are three periodic evolution laws of mining fractures: “half period”, “single period” and “double period”. Based on the characteristics of mining rock and soil activities, a block structure model of gully soil layer is established, and the periodic activity characteristics of mining fractures are analyzed in loess hilly areas.
(3)The coupling relationship between bedrock and soil layer during mining overburden migration region is analyzed in loess hilly areas. Based on the characteristics of mining instability between bedrock and soil layer, a “rock chain” structure model of bedrock is established, and the dynamic development process of mining fractures is analyzed in bedrock, and the fracture development type caused by the instability of bedrock structure under linear load is obtained. In the gully soil layer, the prediction model of gully slope movement and deformation is established, and the formation mechanism and characteristics of different types of mining fractures are given. By introducing the additional stress of gully slope, the stress state of soil element in shallow gully soil layer is analyzed, and the criterion of “tensile failure” of mining fractures under gully is given. Based on the linear load mechanical model of deep gully soil layer, the criterion of “shear failure” and “tensile failure” of mining fractures up gully in loess is given.
(4)By using UDEC numerical simulation software, numerical models of different factors such as mining direction of working face, slope angle, bedrock thickness and soil thickness were established. It was concluded that the reverse slope mining destroyed the integrity of the slope in the early mining stage, and the mining fractures were more developed than that in the downslope mining. With the increase of slope angle, the horizontal displacement of slope increases nonlinearly, and the movement range of slope also expands. With the increase of bedrock thickness, the overall strength of bedrock increases, and the movement of slope decreases, which weakens the development of mining fractures. With the increase of soil layer thickness, the displacement and range of slope body decrease less, and compared with the increase of the same bedrock thickness, the retarding effect on the development of mining fractures in slope is limited.
(5)The distribution space of mining fractures is divided into “four zones and three zones”, and the prediction model of surface movement and deformation in loess hilly is established to analyze the morphological characteristics of different types of fractures. By establishing the geometric model of the morphology characteristics of mining fractures in “I” and “V” plates, the relationship between the equivalent width of mining fractures and the velocity of tracer gas is derived. Based on the relationship between the two, the SF6 tracer gas technique was used to detect the dynamic and regional characteristics of mining fractures in loess hilly areas.
谷歌
火狐
