Key Takeaways & Executive Findings
- •• A new calculation model for deformation energy of tectonic coal based on critical state theory is proposed, which accounts for nonlinear constitutive behavior. • The relationship between deformation energy and stress follows a power law, with exponents close to 2 for intact coal and 1 for tectonic coal. • Coal viscosity and viscoelastic behavior significantly influence cyclic loading/unloading curves, leading to increased deformation energy with load cycles. • Tectonic coal exhibits deformation energy an order of magnitude higher than intact coal under the same stress, highlighting its role in coal and gas outbursts.
Abstract
The deformation energy (Wd) of soil-like tectonic coal is crucial for investigating the mechanism of coal and gas outbursts. Tectonic coal has a significant nonlinear constitutive relationship, which makes traditional elastic-based models for computing Wd unsuitable. Inspired by critical state soil mechanics, this study theoretically established a new calculation model of Wd suitable for the coal with nonlinear deformation characteristics. In the new model, the relationship between energy and stress no longer follows the square law (observed in traditional linear elastic models) but exhibits a power function, with the theoretical value of the power exponent ranging between 1 and 2. Hydrostatic cyclic loading and unloading experiments were conducted on four groups of tectonic coal samples and one group of intact coal samples. The results indicated that the relationship between Wd and stress for both intact and tectonic coal follows a power law. The exponents for intact and tectonic coal are close to 2 and 1, respectively. The stress-strain curve of intact coal exhibits small deformation and linear characteristics, whereas the stress-strain curves of tectonic coal show large deformation and nonlinear characteristics. The study specifically investigates the role of coal viscosity in the cyclic loading/unloading process. The downward bending in the unloading curves can be attributed to the time-dependent characteristics of coal, particularly its viscoelastic behavior. Based on experimental statistics, the calculation model of Wd was further simplified. The simplified model involves only one unknown parameter, which is the power exponent between Wd and stress. The measured Wd of the coal samples increases with the number of load cycles. This phenomenon is attributed to coal’s viscoelastic deformation. Within the same stress, the Wd of tectonic coal is an order of magnitude greater than that of intact coal. The calculation model of Wd proposed in this paper provides a new tool for studying the energy principle of coal and gas outbursts.
1. Introduction
Coal and gas outburst (CGO) is a serious disaster that poses a significant threat to the safety of coal mining. It causes the rapid ejection of a large amount of coal and gas into the roadway within a very short period and can further trigger gas explosions [1]. Although China has implemented extremely strict measures for preventing gas disasters, outburst accidents still occur from time to time [2,3]. Scholars have proposed various hypotheses attempting to explain the mechanism of CGOs, but there is currently no unified understanding [4,5]. Energy analysis is an essential method for studying the mechanism of CGOs, providing a quantitative approach to establishing the critical conditions for the triggering of CGO disasters [6,7]. Coal deformation energy and gas expansion energy are the two main sources of power for CGOs, providing the necessary energy for the high-degree pulverization and long-distance transportation of the outburst coal [8,9]. Research on characterization methods for the energy sources of CGOs is of great significance for revealing the mechanisms of CGOs [10].
The combined effect hypothesis, a well-known perspective, states that the CGO is jointly influenced by in-situ stress, gas, and coal properties [11]. Although the combined effect hypothesis has been widely approved, the contribution of coal deformation energy in outbursts is often underestimated compared to gas expansion energy. Some literature [12,13] indicates that the gas
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Chenghao Wang, Haisong Liu, Yuanping Cheng, Liang Wang, Jingyu Jiang (2024). Deformation energy of tectonic coal under hydrostatic conditions: A new calculation model based on critical state theory. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2024.12.010
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Frequently Asked Questions
What is the main contribution of this paper?
The paper proposes a new calculation model for the deformation energy of tectonic coal under hydrostatic conditions, based on critical state soil mechanics, which accounts for the nonlinear constitutive behavior of tectonic coal.
How does the deformation energy of tectonic coal differ from that of intact coal?
The deformation energy of tectonic coal is an order of magnitude greater than that of intact coal under the same stress, and the relationship between deformation energy and stress follows a power law with exponents close to 1 for tectonic coal and 2 for intact coal.
What role does coal viscosity play in the cyclic loading/unloading process?
Coal viscosity, particularly its viscoelastic behavior, causes downward bending in the unloading curves and leads to an increase in measured deformation energy with the number of load cycles.
What is the simplified calculation model proposed in the paper?
The simplified model involves only one unknown parameter, which is the power exponent between deformation energy and stress, making it practical for engineering applications.
Why is the new model important for studying coal and gas outbursts?
The new model provides a more accurate tool for quantifying the deformation energy of tectonic coal, which is a key energy source in coal and gas outbursts, thereby improving the understanding of outburst mechanisms and aiding in prevention.
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