复杂应力路径下原煤力学与渗透特性试验

Tests on mechanical and permeability characteristics of raw coal under complex stress paths

运用自主研制的煤岩热流固耦合试验系统,以原煤为研究对象,进行轴压、围压分别循环加卸载试验,分析在轴压和围压的作用下原煤的力学特性和渗透特性。研究结果表明:随着轴压加载程度的增大,轴压加载过程中的塑性变形程度也增大。通过定义累积塑性变形量δε、累积渗透率变化量δK、累积体应变变化量δεV得出:在轴压循环加卸载至较低程度时,径向累积塑性变形量δε3和轴向累积塑性变形量δε1对δK的影响大致相同;随着轴压循环加卸载至更高的应力,δε3对相同δK的变化相较δε1更敏感,从δεV在完全由δε1、2δε3的影响这一极限假设情况下,径向变形量相较轴向还是更敏感。轴压完成加卸载并保持不变,轴向变形随围压的加卸载呈线性减小。而径向变形与围压在加卸载时也具有很好的线性拟合关系,径向变形随围压加卸载呈"V"形变化,渗透率呈倒"V"形变化。在轴压加载值较小时,对围压进行加卸载时,围压对煤样的塑性发展影响不大。

A series of cyclic loading and unloading tests on raw coal is conducted under the conditions of axial compression and confining pressure using self-developed servo-controlled seepage equipment for thermal-hydro-mechanical coupling of coal. The mechanical properties and permeability characteristics of coal are analyzed under different axial compressions and confining pressures. The results show that the plastic deformation degree SD increases with the increase of axial compression degree. Cumulative plastic deformation δε, cumulative amount of permeability variation δK and cumulative volumetric strain variation δεv are defined, and some conclusions are drawn with the use of those parameters. At a relatively low level of axial loading-unloading, the cumulative plastic deformation δε3 and δε1. have the same effect on the cumulative permeability variation δεK with the increase of σ1, δε3 is more sensitive to the change of δK than δK Assuming an extreme scenario, i.e., δεv is determined only by δε1 and δε3, the radial deformation is found more sensitive than axial deformation. The axial compression remains constant, and the axial deformation decreases linearly with the change of confining pressure. Radial deformation ε3 and σ3 also has a good linear fit. ε3 presents V-shape, and the permeability exhibits inverted V-shape. When axial load is at a low level, the loading-unloading of confining pressure does not have a significant impact on the development of plastic deformation.