Abstract
Shallow and thick coal seams occur extensively in hilly areas in Shanxi Province and Shaanxi Province, China. The surface damage and landslides caused by shallow fully mechanized caving mining have a very serious impact on the environment. To provide a theoretical and reference foundation for mine environmental protection in hilly settings, a research on surface movement of the high-intensity fully mechanized caving mining working face with shallow thick bedrock and thin epipedon (HIFMCMWFSTBTE) is urgently needed. In this study, using the P2 working face of a mine as the research object, three surface subsidence observation lines were arranged in this working face to analyze the dynamic change characteristics of surface subsidence. Besides, the law of surface movement, mining sufficiency, fracture development and distribution characteristics, subsidence speed, and surface movement duration of HIFMCMWFSTBTE in hilly areas were comparatively studied. The research results reveal that the upper part of the slope slides towards the downhill direction under the action of tensile stress or push stress. As a result, the range of the horizontal movement towards the downhill direction of the slope and the range of surface movement both increase, and the movement angle and boundary angle both decrease compared with the plain. HIFMCMWFSTBTE is prone to serious sudden discontinuous damage. Fractures on the gully region surface develop along the contour, forming a crisscross fracture network, and the fractures are not easy to close after being generated. HIFMCMWFSTBTE in hilly areas can achieve full mining more easily than those of other geological conditions. According to the field measurement, critical full mining can be achieved in P2 working face when the ratio of mining width to mining depth is 1.07. The surface movement duration of HIFMCMWFSTBTE in hilly areas is relatively short. Considerable subsidence will occur in the active stage, and the surface subsidence is sudden and violent. The measured surface stabilization time of the P2 working face is only 20% of the calculated value in the Specification for Coal Pillar Reservation and Coal Mining under Buildings, Water Bodies, Railways, and Main Shafts (hereinafter referred to as the Specification), indicating that the specification's empirical formula is inapplicable to the calculation of surface stabilization time of the P2 working face.
Highlights
Before an underground coal seam is mined, the rock remains in a relatively balanced state under the action of in situ stress field
Song et al [6, 7] investigate the evolution of deformation and damage related parameters as well as the hysteresis behavior on Tibet marble. e test results show that an increase of FT cycles and fatigue load level both accelerate the damage rate of marble
Based on two different cyclic loading strategies, it is concluded that the maximum load level has a more pronounced effect on energy dissipation than the minimum load level [8]
Summary
Before an underground coal seam is mined, the rock remains in a relatively balanced state under the action of in situ stress field. Useful conclusions were drawn through a series of studies on the mining-induced surface subsidence from the aspects of bedrock thickness, buried depth, mining sufficiency, and so on It is found in relevant researches [15,16,17] that due to the influence of surface topography, the surface topography damage, subsidence law, and construction protection of hilly areas are quite different from those of plain areas. Shallow and thick coal seams occur extensively in hilly areas in Shanxi Province and Shaanxi Province, China In view of this fact, with the fully mechanized caving mining P2 working face with shallow thick bedrock and thin epipedon in a mine taken as the engineering research object, the temporal and spatial evolution laws of surface movement in HIFMCMWFSTBTE in hilly areas under the same mining and geological conditions were summarized by combining the methods of field measurement and theoretical analysis.
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