Abstract
The Jurassic coal fields in western China are characterized by thick coal seams and weak overburden. The height of an interconnected fracture zone (HIFZ) is often abnormally high for fracture zones produced by coal seam mining. In this paper, HIFZ is discussed through theoretical analysis, in-situ investigation, and data fitting with regression analysis. A comparison of two calculation methods in this study indicates the applicability of calculating HIFZ by the first method, based on the mechanical relationships among fractured rock strata, i.e., (i) the flexural and breaking limit conditions of roof rock mass, (ii) influence of rock fragmentation and bulking, and (iii) thickness of excavated coal seam. In the second method, an analytical formula of HIFZ is obtained by a fitting regression analysis on the measured data of coal mines under similar geo-mining conditions. For the HIFZ in working face 103 of the Zhuanlongwan coal mine, the two calculation methods yield values of 109.74 m and 92.91 ∼ 114.57 m, respectively. The measured value is 107.67 m, obtained using the method of drilling double-end sealing and water leakage measurement. The results of both theoretical calculations are mostly consistent with the measured value, which verifies the effectiveness of the two prediction methods.
Highlights
The developing characteristics of an interconnected fracture zone have been extensively investigated (Duboeuf et al, 2017; Huang et al, 2018; Ma et al, 2020; Ning et al, 2019; Raziperchikolaee and Miller, 2015)
The results obtained from theoretical formula prediction and numerical simulation analysis are generally quite different from those obtained through in-situ investigations
Where H is the height of an interconnected fracture zone (HIFZ) obtained by the initial fissure subsidence (m), H’ is that obtained by the periodic fissure subsidence (m), hj is the thickness of rock layer j (m), kj is the coefficient of rock fragmentation and bulking of layer j, h is the coal seam mining height (m), and wpi and wzi indicate the critical subsidence of initial and periodic failures of the rock stratum i, respectively
Summary
The developing characteristics of an interconnected fracture zone have been extensively investigated (Duboeuf et al, 2017; Huang et al, 2018; Ma et al, 2020; Ning et al, 2019; Raziperchikolaee and Miller, 2015). The mechanical conditions of rock beam fracture, combined with equations (3) and (5) to (7), are used to derive the tensile stress of C2, as follows: 1⁄2rt
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