Before a coal mining operation, it is necessary to carry out coal-bed methane (CBM) pre-extraction to prevent coal and gas explosions, causing accidents. However, gas extraction and coal mining will lead to coal damage, which results in a change in the gas migration law. Especially, under deep mining conditions, the gas migration mechanism is more complicated owing to a high ground temperature. Coal permeability is the most important constituent that determines gas flow properties. Therefore, the coal permeability evolutionary law related to damage-induced conditions under different temperatures should be further researched. In this paper, a series of triaxial seepage experiments during the whole stress-induced process, and in the changing of the effective stress process were carried out. The results have shown that during the whole stress–strain process, with an increase in axial strain, coal permeability gradually decreases to a minimum value at first, then increases sharply, and finally keeps nearly constant. A higher temperature resulted in a lower elastic modulus, peak strain, and peak strength, but it caused higher thermal damage. When the coal fractures, coal permeability increases with the increase in temperature. During a change in the effective stress process, higher temperatures resulted in higher permeability. Under higher effective stress, the impact of temperature on permeability was not significant. Based on the above results, a novel damage-based permeability model was developed to describe the permeability evolutionary law caused by damage-induced conditions under compaction, and in a fracturing situation. In the proposed model, an exponential function has been used for the combination between permeability and damage variable. The damage variable is composed of thermal damage and mechanical damage. In addition, the damage variable has been modified by introducing a modified function of the initial damage. Finally, the proposed model has been applied to fit two sets of experimental data available. The fitting results showed that the proposed permeability model could well reflect the permeability behaviors of damage-induced coal at different temperatures.

中文翻译：

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不同温度条件下煤压裂过程中基于损伤的新型渗透率模型

煤矿开采作业前，需要进行煤层气预抽，防止煤、瓦斯爆炸，造成事故。然而，瓦斯开采和煤炭开采会导致煤损，从而导致瓦斯运移规律发生变化。特别是在深部开采条件下，由于地温较高，气体运移机制更加复杂。煤的渗透性是决定气体流动特性的最重要的组成部分。因此，应进一步研究不同温度下与损伤诱导条件相关的煤渗透率演化规律。本文在整个应力诱导过程和有效应力变化过程中进行了一系列的三轴渗流实验。结果表明，在整个应力-应变过程中，随着轴向应变的增加，煤的渗透率先逐渐降低到最小值，然后急剧增加，最后几乎保持不变。较高的温度导致较低的弹性模量、峰值应变和峰值强度，但会导致更高的热损伤。当煤体破裂时，煤体的渗透率随着温度的升高而增加。在有效应力变化过程中，较高的温度导致较高的渗透率。在较高的有效应力下，温度对渗透率的影响不显着。基于上述结果，建立了一种新的基于损伤的渗透率模型来描述压实和压裂情况下损伤诱导条件引起的渗透率演化规律。在所提出的模型中，指数函数已被用于渗透率和损伤变量之间的组合。损伤变量由热损伤和机械损伤组成。此外，通过引入初始损伤的修正函数来修正损伤变量。最后，所提出的模型已应用于拟合两组可用的实验数据。拟合结果表明，所提出的渗透率模型能够较好地反映不同温度下损伤致煤的渗透率行为。最后，所提出的模型已应用于拟合两组可用的实验数据。拟合结果表明，所提出的渗透率模型能够较好地反映不同温度下损伤致煤的渗透率行为。最后，所提出的模型已应用于拟合两组可用的实验数据。拟合结果表明，所提出的渗透率模型能够较好地反映不同温度下损伤致煤的渗透率行为。