液氮对不同温度煤裂隙冻融扩展作用研究

Study on effect of freeze-thaw cycle with liquid nitrogen on crack extension of coal at different initial temperatures

为研究液氮冻融循环作用对煤内原生裂隙扩展和抗压强度的影响,选取初始温度分别为35,55和75℃的原煤煤样,采用激光共聚焦显微镜、声波测速仪测试煤样经液氮冻融前后的裂隙扩展程度,通过单轴压缩试验研究冻融循环前后煤样抗压强度的变化规律。结果表明,液氮冻融循环对煤裂隙的发育有促进作用,相同冻融循环周期下试样裂隙宽度扩展量随初始温度升高而增大;相同初始温度下试样裂隙宽度扩展量随冻融循环周期数的增加而增大,试样裂隙沿垂直节理方向扩展明显;55和75℃煤样破坏周期数分别为8和9。

In order to research the effect of liquid nitrogen freeze-thaw cycle on the original crack propagation and compressive stress of the coal,freeze-thaw cycle experiments with liquid nitrogen were carried for coal samples at different initial temperatures 35 ℃,55 ℃ and 75 ℃. Laser confocal microscope and sound velocimeter were used to monitor the crack propagating amount of the coal samples before and after freeze-thaw cycles. The change law of sample＇s compressive strength was studied by uniaxial compression experiments. The results show that freeze-thaw cycle with liquid nitrogen contributes to the crack extension,the width of crack in coal samples under the same freeze-thaw cycle increases with the temperature increasing,that the crack propagating amount of the samples at the same initial temperature is a function of the number of the freeze-thaw cycles,the extension direction of crack is perpendicular to the joint direction,and that the freeze-thaw cycles＇ number resulting in sample breakdown is a function of the initial temperature-8 at 55 ℃ and 9 at 75 ℃.