关键词:

煤炭地下气化 , 砂岩 , 单向加热 , 声发射 , 裂隙演化 , 分形维数

Abstract: The high temperatures generated in the combustion area during underground coal gasification can cause structural damage to the roof rock. In order to study the effect of thermal damage caused by different temperatures (100 ℃, 200 ℃, 300 ℃, 400 ℃, 500 ℃, 600 ℃) on the acoustic emission characteristics and rupture mechanism of sandstone. The acoustic emission signals were collected and analyzed during the test by using the self-developed unidirectional heating experimental equipment. Research has shown that the positive correlation between the cumulative number of acoustic emission events and the number of internal cracks can better reflect the macroscopic damage scale of sandstone, with the most obvious fracture occurring at 400 ℃ -500 ℃. On the micro-damage, the cracks develop fast in the rapid warming stage of each temperature of the specimen. With the increase of temperature, the proportion of low-frequency decreased by 56.02%, and the proportion of high-frequency increased by 57.1%, and the main frequency was changed from low-frequency dominated to high-frequency dominated, i.e., the damage of sandstone was transformed from the dominance of intergranular slip to the dominance of fissure extension. Thermal damage of sandstone is a process of expansion and deformation, crack initiation, rapid development and cracks continue to develop through to destruction. Sandstone crack sprouting, crack development and crack nonstationary development correspond to changes in fractal dimension values of 0.35, 0.15 to 0.35, and -0.15, respectively, respectively. The mutation point between the irregular fluctuation phase and the sudden drop phase of the fractal dimension curve can be used as a signal to predict the formation of internal macroscopic fissures during the thermal rupture of the rock, which provides theoretical support for the design of reasonable mining width for underground coal gasification.