有效应力对煤体力学特性影响试验研究

Experimental study of the impact of the effective stress on the mechanical properties of the coal

为揭示煤与瓦斯突出灾害机理,综合考虑地应力和瓦斯压力对煤体力学特性的影响,采用有效应力进行分析。在不同围压、不同瓦斯压力条件下进行煤体受载破裂试验,综合分析围压、瓦斯压力和有效应力对煤体力学特性影响。结果表明:围压载荷使煤体抵抗变形能力变强,瓦斯压力载荷使煤体抵抗变形能力变弱;有效应力相同时,煤体压密效果相同,只受到围压作用的煤体单轴抗压强度高、弹性模量低,达到峰值应力后抵抗变形能力强;同时受到围压载荷和瓦斯压力载荷,且有效应力相同时,煤体压密阶段和弹性变形阶段具有相同的压密效果、弹性模量和单轴抗压强度。对井下煤体进行有效应力分析,可以简化力学模型,为分析井下煤岩力学状态提供方法。

In order to reveal the mechanism of coal and gas outburst, the paper is inclined to study the influence of the ground stress and gas pressure on the mechanical properties of the coal,and used the effective stress to analyze it. To study the impact of the confining pressure, gas pressure and the effective stress on the mechanical properties of the coal respectively, we have conducted the coal deformation and rapture tests under different conditions, including the tests under different confining pressures with and without the gas influence, the tests under different confining pres- sures and the same gas pressure, in the presence of the contrasting gas test under the same effective stress. Furthermore, we have also analyzed the effects of the confining pressure, gas pressure and effective stress on the mechanical properties of the in a comprehensive way. The results of our study prove that： on the condition that the confining pressure ranges from 0 to 8 MPa, the greater the confining pressure is, the stronger the coal ability to resist deformation will be. Moreover, the confining pressure has been found inhibiting the appearance and the accumulating effect of coal crack. Besides, when the gas pressure ranges from 0. 3 MPa to 1.3 MPa, the greater the gas pressure is, the weaker the coal ability to resist the deformation will be. At the same time, the gas pressure tends also to have promoting effects on the taking place of such coal crack accidents. On the condition when the ef- fective stress is same, there would be no densification effect of the coal, witb only tbe presence of high uni-axia] compressive strength and low elastic modulus under confining pressures. What is more, the tendency to resist the deformation can likely be so strong as to reach the maximum extent. What is more, under the confining pressure and gas pressure with the same effective stress, it will be possible for the intensification stage and elastic deforma- tion stage to produce the same densification effect, with the same elasticity modulus at the uniaxial compressive strength. There- fore, it can be concluded that it may have a great help to analyze the mechanical effects of the coal and the impact of the confining pressure and gas pressure on the mechanical properties of the coal, which should be an effective approach to disclosing the coal and gas outburst mechanism and reducing the mining accidents so as to enhance the safety production of coal mining.