Abstract
Roof rocks in coal mines are subjected to the combination of in situ stresses and dynamic stresses induced by mining activities. Understanding the mechanical properties of roof rocks under static and dynamic loads at medium strain rates is of great significance to revealing the mechanism of rock bursts. In this study, we employ the digital image correlation (DIC) technique to investigate the energy concentration and dissipation behaviors, failure mode, and deformation characteristics of roof rocks under combined static and dynamic loads. Our results show that both the static pre-stress and dynamic loading rate have significant effects on the uniaxial compressive strength of rock specimens. From the energy principle, when the static pre-stress is the same, both elastic strain energy density and dissipated energy density increase with increasing dynamic loading rate. The hazard of rock bursts increases with decreasing static pre-stress and increasing dynamic loading rate. At higher dynamic loading rates, more cracks are generated, and the failure becomes more violent. The crack initiation, propagation and coalescence processes are identified, and the failure mode is closely related to the evolution of the global principal strain field of the rock specimens.
Highlights
Rock bursts have become more and more severe and occurred frequently with the increase in mining depth over the years at the rate of 10–25 m per year, and a growing number of mines reach a depth of 1000 m [1,2]
The deep coal extraction is facing stress concentration with acute occurrence and frequency of rock burst incidents induced by dynamic loads in coal mines
Where S1 is the superimposed uniaxial compressive strength (SUCS) when the dynamic loading rate is 2 × 10−3 s−1, and R is the ratio of static pre-stress to the uniaxial compressive strength (UCS)
Summary
Rock bursts have become more and more severe and occurred frequently with the increase in mining depth over the years at the rate of 10–25 m per year, and a growing number of mines reach a depth of 1000 m [1,2]. The deep coal extraction is facing stress concentration with acute occurrence and frequency of rock burst incidents induced by dynamic loads in coal mines. In China, nearly 300 coal mines have reported rock burst disasters so far, and the number is increasing [11]. This table clearly reveals one common characteristic among the causes of rock bursts: stress concentration and dynamic load disturbance. Stresses in coal mines include initial stress and mining-induced stress [12], and the local concentrated high stress is the internal cause of rock bursts.
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