加卸载下原煤力学特性及渗透演化规律

Mechanical characteristics and permeability evolution rule of coal under loading-unloading conditions

基于自主研发的煤岩热流固耦合试验系统,在考虑实际开采方式的条件下,进行轴压升高和围压降低的加卸载试验,分析研究不同加卸载速率下原煤的力学特性和渗透演化规律.结果表明:加卸载过程中,轴向应力的加载速率越大,峰值应力附近的曲线平台越长,峰值应力、轴向应变和环向应变也越大,体应变则越小.不同加卸载速率比下含瓦斯煤变形模量均先迅速减小后缓慢减小,到破坏时再迅速降低,而后逐渐保持稳定趋势;在相同轴向应变时,加卸载速率比越小,煤样的变形模量越大.加卸载过程中,煤样的偏应力、渗透率与应变的关系可分为三个阶段:初始压密与弹性阶段、屈服破坏阶段和破坏后阶段.加卸载速率比越小,煤样达到峰值应力时,含瓦斯煤的渗透率和体积变形越大.

Based on the self-made servo-controlled seepage equipment for thermal-hydrological-mechanical coupling of coal and rock, a loading and unloading experimental study was performed by increasing the axial compression and decreasing the confining pres- sure in consideration of the actual mining method. The mechanical characteristics and permeability evolution rule of coal were analyzed and studied under loading-unloading conditions. The results show that during the process of loading and unloading, the faster the load- ing rate of axial stress, the longer the platform of the stress-strain curve near the peak, and the larger the peak stress, axial strain and circumferential strain, while the smaller the volume strain. The deformation moduli at different loading and unloading rates exhibit the trend of rapidly decreasing first and then slowly decreasing. When damage occurs, the deformation modulus rapidly decreased and then is nearly constant. Under that condition of the same axial strain, the deformation modulus increases with the decrease of loading and unloading rate. The relations of deviatoric stress and coal permeability with strain can be divided into three stages in the whole test process ： initial compaction and elastic stage, yield stage, and post-failure stage. During the process of loading and unloading, the slo- wer the loading and unloading rate is, the larger the coal permeability and volume strain become when the axial stress of coal samples reaches the peak value.