Abstract

The plastic zone of the roof surrounding rock continues to expand after the coal seam mining. The permeability of the surrounding rock under plastic flow is a basic project for water inrush prevention in coal mine. In this work, the permeability experiments were carried out on roof sandstone from Xiaojihan No.2 coal seam under three loading paths. The variations of permeability affected by the confining pressure and axial strain were obtained. In the plastic flow stage, the permeability of roof sandstone was a multivalued function of volumetric strain and confining pressure. The permeability decreased with the increasing confining pressure. As the loading and unloading times increased, permeability was less affected by the confining pressure. and the permeability recovery coefficient increased. Based on the above analysis, the impacts of volume deformation and shear deformation on permeability were analyzed. A permeability model with two coefficients was proposed which was implemented by taking the normal strain and shear strain on the shear plane as independent variables. Through a permeability test with a simple loading path, the optimal estimated value of the permeability influence coefficient was determined by using the Monte Carlo method. It was applied to calculate the permeability under the other two complex loading paths. The calculation results show that the permeability coefficient is the basic attribute of rock materials and irrelevant to the loading path. Essential parameters obtained in this research are useful to analyze the coupled dynamic system’s stable structure of the surrounding rock, and also could serve as theoretical foundations for the water inflow prediction in a coal mine.

Article highlights

1. 1.

   The law of permeability with confining pressure and volumetric strain is obtained in the plastic flow stage.

2. 2.

   Permeability of sandstone is a multivalued function of volumetric strain and confining pressure in the plastic flow stage.

3. 3.

   Proposing a new permeability model to calculate the permeability under complex loading paths.

4. 4.

   The research results provide experimental parameters for the structural stability analysis of the coupled dynamic system.

中文翻译：

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塑性流动下含水层煤层顶板砂岩渗透率演化机制研究

摘要

煤层开采后顶板围岩塑性区继续扩大。塑性流作用下围岩的渗透性是煤矿防突水的一项基础工程。本文对小冀寒2号煤层顶板砂岩进行了三种加载路径下的渗透性试验。得到了围压和轴向应变对渗透率的影响。在塑性流动阶段，顶板砂岩的渗透率是体积应变和围压的多值函数。渗透率随着围压的增加而降低。随着装卸次数的增加，渗透率受围压的影响较小。渗透率恢复系数增加。根据以上分析，分析了体积变形和剪切变形对渗透率的影响。提出了以剪切平面上的法向应变和剪切应变为自变量的具有两个系数的渗透率模型。通过简单加载路径的渗透率测试，利用蒙特卡罗方法确定渗透率影响系数的最佳估计值。用于计算其他两种复杂加载路径下的渗透率。计算结果表明，渗透系数是岩石材料的基本属性，与加载路径无关。本研究获得的基本参数有助于分析耦合动力系统的围岩稳定结构，

文章亮点

1. 1.

   在塑性流动阶段得到了具有围压和体积应变的渗透率规律。

2. 2.

   砂岩的渗透率是塑性流动阶段体积应变和围压的多值函数。

3. 3.

   提出了一种新的渗透率模型来计算复杂加载路径下的渗透率。

4. 4.

   研究结果为耦合动力系统的结构稳定性分析提供了实验参数。