Research on formation mechanism of the mining-induced horizontal fractures in rock strata separation in the Jurassic coalfield, Huang long, Shaanxi, China

Abstract

To analyze the mining-induced mechanism of the horizontal fractures due to bed separation in Jurassic coalfield, China, the mineral composition identification test, triaxial compression tests, and overburden response were performed in this study. The mineral composition of rocks is composed of terrigenous sand (cuttings, quartz, and feldspar), terrigenous silt, clay, and a few interstitial materials in adjacent rock strata. The differences of mineral compositions are proved to be the essential factors through triaxial compression tests on rock samples, which found that the strength, Young’s modulus, Poisson’s ratio, and plasticity of adjacent have great differences in rock samples. For predicting the variation of the horizontal fractures, the overburden is supposed to be a thin cube plate. And the range of sizes is corresponding to the scope of the extracted coal seam. Then, based on the elasticity thin plate theory, w(x, y)=C0(1+cos(xπ/a)) (1+cos(yπ/a)) is proposed as the deflection function and the stress and deformation of rock strata are obtained by the variational method and minimum potential energy principle. Hence, a mathematical model suitable is proposed to analyze the variation of the horizontal fractures. The Yuanzigou coal mine is taken as an example, the theoretical results are verified by an exploration borehole video imager. In conclusion, the distribution characteristics of rock strata and the differences in these physical parameters are the essential factors causing horizontal fracture between adjacent rock strata. Besides, the relationship between horizontal fractures and roof water inrush was also discussed in this study.

Keywords

• Horizontal fracture
• Rock strata separation
• Water inrush
• Mining
• Elasticity plate theory