开采扰动下考虑损伤破裂的深部煤体渗透率模型研究

A damage-based permeability models of deep coal under mining disturbance

为了研究深部煤体在开采扰动影响下的渗透率演化规律,以三向应力条件下的煤体渗透率模型为基础,从吸附解吸作用引起裂隙变形和损伤破裂造成煤基质弹性模量劣化的角度进行理论推导,引入内膨胀应变系数的概念,同时基于Drucker-Prager破坏准则的损伤本构关系建立了两种考虑煤体损伤破裂的渗透率演化模型——指数型和立方型,并且对常规三轴加载、开采扰动加卸载和改变气体压力下的瓦斯渗透试验结果进行了拟合分析。结果表明:所构建的两种模型可以较好地反映常规三轴加载和开采扰动加卸载下煤体渗透率的分区段变化特征,也可以描述有效围压恒定条件下煤体渗透率随气体压力升高而降低的规律。在开采扰动加卸载和改变气体压力的试验中,指数型的拟合效果略优于立方型。研究结果可为深部煤炭开采及瓦斯抽采的工作提供指导。

To investigate the permeability evolution of deep coal under the influence of mining disturbance, two forms of permeability model including the damage and fracture effect were established. These two forms were exponential form and cubic form, respectively. These two permeability models were based on the previous coal permeability model in three-dimensional（3 D） stress state. The derivation process included two aspects, i.e., the fracture deformation caused by adsorption and the deterioration of elastic modulus from matrix caused by damage. Meanwhile, the internal swelling ratio and the damage constitutive based on Drucker-Prager failure criterion were introduced into the models. According to permeability tests under conventional triaxial compression, loading-unloading under mining disturbance and changing the gas pressure, the permeability of coal in the tests were analyzed in detail. The results show that these two models can reflect the permeability evolution in the conventional triaxial compression and loading-unloading tests. Moreover, these two models can represent the decrease of coal permeability with the increase of gas pressure under the constant effective confining pressure condition. In the loading-unloading and changing the gas pressure tests, the fitted results in exponential form are slightly better than those in cubic form. This study provides a useful reference for developing the technology of deep coal mining and gas extraction.