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为了研究温度载荷作用下煤层露头火区上覆岩层受热破坏特性,揭示上覆岩层的强度和变形特征随温度的变化规律。采用MTS8 15.02电液伺服岩石力学试验系统和NM-4A型非金属超声检测分析仪,对岩样进行了25~600℃加温加载试验。试验得出了不同温度条件下岩样受热破坏特征和纵波波速变化规律。结果表明,随温度升高,岩样纵波波速逐渐减小,600℃时砂岩X、Y、Z 3个方向的纵波波速下降了48.54%。高温对岩样的强度有一定的弱化作用,其峰值应力随温度升高而降低,600℃时岩样强度降幅达47.1%。岩样的峰值应变随温度升高而逐渐增大,400℃时峰值应变增大了55.6%,600℃时峰值应变增大了60.9%。随温度升高,砂岩的弹性模量、变形模量均减小,400℃时弹性模量降幅达13.5%,600℃时弹性模量降幅达59.6%。这表明在大面积高温火区的作用下,煤层露头火区上覆岩层产生大量漏风裂隙,热风压增大,致使高温煤体上部空气通过裂隙发生自然对流,从而维持煤体附近一定浓度的氧气。
In order to study the thermal failure characteristics of overburden strata in outcrop fire zone under temperature load, the intensity and deformation characteristics of overburden strata with temperature are revealed. MTS8 15.02 electro-hydraulic servo rock mechanics test system and NM-4A non-metallic ultrasonic testing analyzer were used to test the rock samples at 25 ~ 600 ℃. The experimental results show that under different temperature conditions, the characteristics of rock failure and the variation of longitudinal wave velocity are obtained. The results show that with the increase of temperature, the longitudinal wave velocity of rock samples decreases gradually, and the velocity of longitudinal wave in X, Y and Z directions decreases by 48.54% at 600 ℃. The high temperature can weaken the strength of rock samples, and the peak stress decreases with the increase of temperature. The strength of rock samples decreases by 47.1% at 600 ℃. The peak strain of rock samples increases with increasing temperature, the peak strain increases by 55.6% at 400 ℃, and the peak strain increases by 60.9% at 600 ℃. With the increase of temperature, the elastic modulus and deformation modulus of sandstone decreased, the elastic modulus decreased by 13.5% at 400 ℃, and the modulus of elasticity decreased by 59.6% at 600 ℃. This indicates that under the action of a large area of high temperature fire zone, a large number of air leakage fissures are generated in the overburden strata in the coal outcrop fire area, and the hot air pressure increases so that the upper air of the high temperature coal spontaneously convects through the fissure so as to maintain a certain concentration of oxygen .