Abstract
In order to improve ground control of the longwall mining, ground response and mining-induced stress in the longwall panel of a kilometer-deep coal mine are investigated in this study. Field measurements on abutment stress, roof displacement, and fracture development indicate that the region influenced by the longwall mining reaches 150 m ahead of the longwall face. Failure scope of the coal seam, where mining-induced fractures are well developed, ranges from 10 to 13 m inward the face line. Vertical stress concentration coefficient reaches 2.2. Based on the field measurements, a numerical model is moreover developed and utilized to examine the response of the principal stress to the longwall mining. The concentration coefficient, peak point location, and influence scope of the principal stress gradually become stable with an increase in face advancement. Regarding the major principal stress, the concentration coefficient and influence scope are 2.4 and 152 m, respectively, and the peak point locates 13 m inward the face line, which are consistent with the field measurements. With respect to the minor principal stress, the referred coefficient and scope are 1.5 and 172 m, respectively, and its peak point location is 21 m ahead of the face line. The major principal stress in the coal seam rotates from vertical to horizontal direction in the vertical plane parallel with face advance direction. The maximum rotation angle reaches 20°. The minor principal stress first rotates into the referred vertical plane and then it rotates from horizontal to vertical direction at the same speed with the major principal stress in the same plane. Rotation angle of the principal stress in roof strata is greatly enlarged, the rotation trace of which is influenced by the longwall mining and vertical distance above the seam. Based on the relation between rotation trace of the principal stress and face advance direction, the influence of stress rotation on the stability of roof structure is discussed.
Highlights
In the past decade, the depth of underground coal mining increased by 10 to 20 m per year in China [1, 2]
It is widely accepted that serious ground responses are closely related to the stress environment, which is important to the design of the ground control system in the longwall mining. us, the distribution of mining-induced stress and associated ground responses have been extensively studied with many methods in deep coal mines
The concentration coefficient of the vertical stress at its peak point commonly falls between 2 and 4. us, the initial value of the stress sensor should not be larger than a quarter of the largest value. e load-bearing capacity of the borehole stress sensor used in this study is 20 Major principal (MPa). e initial pressure of the injected oil is set to be 5 MPa, which is much smaller than the initial ground stress (24 MPa)
Summary
The depth of underground coal mining increased by 10 to 20 m per year in China [1, 2]. Us, the distribution of mining-induced stress and associated ground responses have been extensively studied with many methods in deep coal mines. Xie et al investigated mining-induced stress distribution in the longwall panel of a kilometer-deep coal mine with borehole stress monitoring method [7]. The study associated with longwall mining in kilometer deep coal mine is limited In such a longwall panel, ground response and stress distribution become more complex. In order to improve the surrounding rock control, ground response and mining-induced stress in a longwall panel with cover depth of more than 1000 m is thoroughly analyzed in the present study. In order to improve the surrounding rock control, ground response and mining-induced stress in a longwall panel with cover depth of more than 1000 m is thoroughly analyzed in the present study. e emphasis is placed on the rotation of the principal stress and potential influences provided by the stress rotation
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