Abstract
The deformation and movement characteristics of high-level key stratums in overlying strata are important for estimating ground subsidence and understanding failure characteristics of ultrathick strata during mining. In this study, a distributed optical fiber sensor (DOFS) and multipoint borehole extensometers (MPBXs) were collaboratively employed to monitor the deformation of high-level key stratums in situ during the mining process at working face 130,604 of the Maiduoshan Coal Mine. DOFS monitoring results showed that the distance from advance influence of mining on the ground surface is 219.2 m. The deformation of the shallow stratums were greater and was affected earlier than that of the deep stratums. The deformation in the strata did not occur continuously and the boundary curve of the impact from advance mining was not a straight line with the advancement of the working face. By the MPBX technology, we measured the strata movement and obtained four-stage characteristics of high-level key stratum movement. The subsidence of the primary key stratum and the sub key stratum were monitored to reach 1389 and 1437 mm; their final relative displacement differed by 48 mm. No bed separation was observed in between the strata, and the key stratums tended to sink as a whole with the advancement of the working face. This research guides the analysis the movement of thick high-level key stratums.
Highlights
Western China has ideal geological conditions to support coal mining
Ultrathick sandstones with a thickness of 40–100 m were found to exist in the overlying strata at 200 m above the coal seam in the Maiduoshan Coal Mine, which results in vibrating ground and serious deformation of the underground roadway along the gob during the mining process at the working face
The movement of the ultra-thick rock formation at a distance that is 10–20 times the mining height above the coal seam will still have a significant effect on the mining pressure. Zhu[10] proposed a structural mechanics model of far-field key stratums in overlying strata at a large coal mine
Summary
Western China has ideal geological conditions to support coal mining. Abundant reserves of extra-thick coal seams with a thickness of 6–20 m or more have been discovered in that region. Stratums with a thickness of 50–100 m were found to exist at 150–180 m above the roof of the coal seam in the Binchang mining area (Tingnan Coal Mine, Shaanxi Province), which have caused more than 40 rock burst accidents in roadway during the mining process at the No 206 working face in the second p anel[5,6]. Zhu[10] proposed a structural mechanics model of far-field key stratums in overlying strata at a large coal mine Such model provides a preliminary explanation for the long-term occurrence of high mining pressure. Several other studies attempted to reveal the relationship between high-level stratum movement and underground pressure by combining different approaches, including surface drilling and monitoring of the underground mining p ressure[14,15,16]. Despite the efforts of researchers, most of the strata movement monitoring attempts performed far have been limited to depths of less than 200 m
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