力热耦合作用下煤岩损伤演化规律及渗透率模型研究

Exploration into the damage evolutionary regularity and the permeability model of the coal strata under the coupling effect of stress and temperature

为探究深部煤体开挖中的损伤演化规律和瓦斯渗流特性,利用含瓦斯煤热-流-固耦合三轴伺服渗流试验装置和HCA型高压容量法吸附装置,分别开展了不同温度下煤岩三轴渗流试验和等温吸附试验,建立了力热耦合条件下煤岩损伤本构模型及考虑热损伤和吸附效应的煤岩渗透率模型。结果表明:1)煤岩变形可分为压密、线弹性、屈服和破坏后阶段,煤岩峰值强度随温度升高而降低,其峰后渗透率随温度升高而增大;2)煤岩损伤分为热损伤和力损伤,热损伤DT随温度升高而增大,建立的煤岩损伤本构模型能精确匹配不同温度下的全应力-应变曲线;3)基于分段和对称函数的数学思想,提出了修正因子L的概念,建立了考虑热损伤及吸附效应的渗透率模型,试验验证了其合理性,可表征不同温度下的渗透率演化特征。

The paper is intended to make an exploration of the damage evolutionary regularity and the gas seepage characteristic features of the in-depth coal through the tri-axial seepage tests and the isothermal adsorption tests at the different temperatures,which can be conducted by using the tri-axial servo seepage equipment and the isothermal adsorption device. In addition,a coal damage constitutive model under the coupling of the stress and temperature and a coal permeability model have been proposed on account of thermal damage and adsorption effect. The results of our exploration show that the temperature has a significant effect on the mechanical properties and the seepage features of the coal. Actually,the deformation of the coal seam evolution can be divided into the compaction stage, the linear elastic stage,the yield stage and the post-failure stage. The peak strength of the coal tends to decrease with the increase of the temperature because the temperature has a deterioration effect on the mechanical properties. Therefore,the adsorption deformation tends to decrease with the increase of temperature due to the enhancement of the desorption and the gas molecular activity induced by the temperature change. On the other hand,the coal permeability tends to increase with the increase of temperature in the post-failure stage. Therefore,the total damage variable can be divided into thermal damage and mechanical damage,with the thermal damage being increased with the increase of the temperature. Based on the D-P failure criteria,we have proposed the damage constitutive model of the coal,which can accurately be matched with the entire stress and strain curve under the different temperatures. And,next,the influence of the slippage effect,the adsorption effect,and the thermal damage effect can be taken as on the basis of the classical exponential permeability model.And,finally,we would like to put forward the concept of the correction factor L,and the piecewise permeability model through the combination between the correction factor L and exponential permeability model. Thus,the permeability test curve and the model’s curve ought to be highly coincided,whereas the improved coal permeability model can be said in a position to be highly applicable and reasonable.