Abstract
Due to the high in situ stresses, dynamic disasters occurred frequently in the Huainan mining area, China. Our understanding of the in situ stresses in this area is still insufficient. In this study, the in situ stresses of 18 sections in two boreholes in the Xinji No. 1 coalfield were measured using the hydraulic fracturing method, and the distribution of in situ stresses in the Huainan mining area were investigated. The relationship between in situ stress and geological structure in the Huainan mining area was summarized and the limitation of fault friction strength on in situ stress was discussed. The result showed that the maximum horizontal principal stress (σH) at Xinji No. 1 mine was 13.95–25.23 MPa, the minimum horizontal principal stress (σh) was 12.16–21.17 MPa. The average azimuth of the maximum horizontal principal stress was N83.61°E. The statistical results showed that the in situ stresses in Huainan mining area were characterized by a strike-slip faulting regime. Both the horizontal and vertical principal stresses increased approximately linearly with the increase of burial depth. The orientation of the maximum principal stress in the study area is closely related to the tectonic movement and the ratio of maximum principal stress to minimum principal stress was primarily limited by the friction strength of the faults. The outcomes of this research can provide some reliable engineering parameters and benefit the roadway layout and support design in the Huainan mining area.
Highlights
In situ stress is the virgin stress that exists in the crustal rock mass and is the fundamental force that causes deformation and failure of surrounding rock in underground engineering excavation
Mastering the in situ stress state in the engineering area is a prerequisite for determining the mechanical properties of the engineering rock mass, analyzing the stability of surrounding rock, and realizing scientific design and decision-making of excavation in geotechnical engineering (Zoback et al, 1985)
Since the 1980s, dozens of countries in the world have carried out a variety of methods of in situ stress measurements, such as hydraulic fracturing, overcoring, borehole caving, and acoustic emission, which have been successfully applied in engineering application, earthquake prediction, oil and coal mining (Gay, 1975; Greiner, 1975; Cornet, 1984; Bell, 2006; Zhao et al, 2015; Oliver et al, 2018)
Summary
In situ stress is the virgin stress that exists in the crustal rock mass and is the fundamental force that causes deformation and failure of surrounding rock in underground engineering excavation. There is a high in situ stress level in the deep of this mining area Disasters such as impact underground appearance, gas outburst and large deformation of roadway surrounding rock occur frequently, which seriously threaten the safety of mine production (Li et al, 2019; Li et al, 2013; Yang et al, 2012). Liu et al (2012) used the hydraulic fracturing and stress relief methods to measure the in situ stress in Xie No 1 mine, Pan No 3 mine and Wangfenggang mine, and analyzed the characteristics of in situ stress field in the deep of the mining area. In combination with previously measured data, the distribution characteristics of the in situ stress in the Huainan mining area were statistically studied, and the influence mechanism of the geological structure on the in situ stress field was discussed. Where σv is the vertical principal stress; H is the occurrence depth of the rock mass
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