Abstract
In the deep mining areas of western China, there exist ultrathick and weak cementation strata in the overburdens above the Jurassic coal seams, and the overburden lithology is generally moderately a little weaker than the medium-hard strata. Yet, the practical measurement indicates that the surface movement rule in this area displays the specialty that is apparently inconsistent with its lithology, which increases the uncertainty of safe production in coal mines. In this study, the similar material and numerical simulations were conducted to investigate the movement rule and failure pattern of the ultrathick and weak cementation overburden. In addition, the photographing scale transformation-time baseline parallax (PST-TBP) method was used to monitor the similar material model to makeup for the lacks of Xi'an Jiaotong University Digital Close-range Industrial Photogrammetry System (XJTUDP) software. The findings of this study can be summarized as follows. (1) To some extent, the PST-TBP method can makeup for the deficiency of the XJTUDP software because the measurement accuracy of the PST-TBP method is 0.47 mm. (2) The height of the caving zone is approximately 66 m, and the height of the water suture zone is about 112 m, which is obviously larger than that of the medium-hard and soft overburden in eastern-central China. (3) The first breaking span of the immediate roof reaches 120 m, the cyclic fracturing length is about 60 m, and the separation occurred at 43 m and 66 m above the coal seam. (4) The failure pattern of the ultrathick and weak cementation overburden is “beam-arch shell,” and the failure boundary is arch. (5) The Zhidan group sandstone and Jurassic sandstone formations have strong control effects. The Zhidan group sandstone is the main control stratum and the Jurassic sandstone formation is the secondary-control stratum. The research results provide an insight into guiding the safe mining of deep coal in the ultrathick and weak cementation overburden.
Highlights
Western China is on its way to become the primary source of coal resources for China in the future
Via field investigations, we analyzed the reasons for the small surface subsidence of deep mining with ultrathick and weak cementation overburden. e similar material and numerical simulations were employed to study the strata movement rule of ultrathick and weak cementation overburden
We applied photographing scale transformation-time baseline parallax (PST-TBP) method to monitor similar material model to compensate for the deficiencies of the digital close-range industrial photogrammetry system (XJTUDP) software. e following findings were obtained: (1) e PST-TBP method can makeup for the deficiency of the XJTUDP software to a certain extent
Summary
Western China is on its way to become the primary source of coal resources for China in the future. E rule of strata movement caused by the middle-shallow coal mining has been well studied by some researchers, such as Ju and Xu [5] who prosed the key stratum theory and Zuo et al [6] who developed a “hyperform” model. Wang [17] and Lin [18] utilized the physical simulation and numerical simulation to investigate the strata movement rule under the condition of deep single working face mining in weak cementation overburdens and examined the causes of the small surface subsidence. In western China, the research on the deep mining area of ultrathick and weak cementation overburden is concentrated on the strata movement rule under the condition of extremely insufficient mining degree or insufficient mining degree. Ere is a lack of research on the stratum movement rule caused by largescale mining deep coal resources under ultrathick weak cementation overburden. Us, this paper primarily applies physical simulation with the support of numerical simulation to deeply conduct the strata movement rule of deep multiple working faces mining of ultrathick and weak cementation overburden, revealing the movement mechanism of ultrathick and weak cementation overburden
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