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利用自行组装的高压气体增压系统开展了原煤煤样的脉冲气压疲劳试验,分析了脉冲次数对原煤煤样变形及渗透性的影响,并对疲劳试验前后煤样的单轴力学特性进行了对比.结果表明:煤样的应变表现出周期性变化,且在一个脉冲气压循环内,煤样体积应变表现为膨胀-收缩.随着疲劳次数增加,残余应变逐渐累积,原煤煤样的轴向应变、环向应变和体积应变均朝膨胀方向增长;在初始疲劳阶段,应变变化较大,当疲劳次数超过一定范围后,原煤煤样的应变基本趋于平衡.原煤煤样的渗透率随脉冲次数的变化与应变类似,开始阶段渗透率随着疲劳次数增加急剧提高,当超过疲劳阈值后,疲劳对煤样渗透率影响较小,其疲劳阈值为50~100.疲劳后原煤煤样的单轴力学性质与没有开展气体疲劳试验的煤样相比,抗压强度、弹性模量显著降低,分别仅为未疲劳煤样的16%和8%,峰值应变则增加了117%,且疲劳后原煤煤样表现出高度体破裂.试验表明在脉冲气压疲劳作用下,煤样内部产生了大量的微裂隙,改善了煤样的渗透率,有利于瓦斯的流动和抽采.
The pulsed pneumatic fatigue testing of raw coal samples was carried out by using self-assembled high-pressure gas pressurization system. The influence of pulse times on the deformation and permeability of raw coal samples was analyzed. The uniaxial mechanical properties of coal samples before and after fatigue test were compared The results show that the strain of coal sample shows periodic change, and the volume strain of coal sample shows expansion-shrinkage in one pulse air pressure cycle.With the increase of fatigue frequency, the residual strain gradually accumulates and the axial strain , Both hoop strain and volume strain increase toward the direction of expansion. During the initial fatigue stage, the strain changes greatly, and when the fatigue frequency exceeds a certain range, the strain of the raw coal tends to balance basically. The permeability of coal samples changes with the number of pulses The change of permeability is similar to that of strain, and the permeability increases sharply with the increase of fatigue number in the initial stage. When the fatigue threshold is exceeded, the fatigue has little effect on the permeability of coal sample and the fatigue threshold is 50-100. Mechanical properties Comparing with coal samples without gas fatigue test, the compressive strength and elastic modulus decreased significantly, which were only 16% and 8% of the un-fatigue coal samples, respectively. The peak strain was increased Plus 117%, and the original coal showed a high degree of body failure after fatigue tests.The experiment shows that under the pulse air pressure fatigue, a large number of micro-cracks are generated in the coal sample to improve the permeability of the coal sample, which is favorable for gas flow and Pumping.