高应力下原煤三轴压缩力学特性研究

STUDY OF MECHANICAL PROPERTIES OF RAW COAL UNDER HIGH STRESS WITH TRIAXIAL COMPRESSION

基于取自淮南矿区-780m标高B10煤层的原煤的试件，通过MTS815．04电液伺服试验系统进行高应力下原煤的常规三轴压缩试验，研究煤岩的变形、强度、参数及破坏特征。研究结果表明：（1）煤岩偏应力一轴向应变曲线主要由弹性、屈服、峰后脆性破坏阶段或应变软化段构成。其中，弹性段明显较长，且围压越大，曲线越陡，弹性模量越大；屈服段则总体较短。（2）煤岩在单轴或低围压条件下，峰后脆性破坏特征明显；随着围压升高，峰后开始呈现延性特征，且围压越高，延性特征越明显。当围压达到50MPa时，峰后轴向应变几乎呈现塑性流动状态。（3）随着围压的增加，峰值轴向应变呈抛物线趋势增加，峰值侧向应变则呈线性增加趋势。（4）煤岩偏应力一体积应变曲线，在低围压条件下表现出扩容机制，且围压越低扩容特征越明显；在高围压下，从峰前越至峰后，则始终向右延展，呈现出不断收缩的状态；而峰值体应变随围压的增加呈抛物线形式增加，收缩特征明显。（5）煤岩强度随围压增加呈线性趋势增加，且强度参数c，φ值分别为12．72MPa，24．12°。（6）煤样的破坏模式主要以剪切破坏为主，破断角大小为23°～35°，且随着围压的增加，以抛物线趋势增加。采用Mohr强度理论可以较好地解释这一变化。

According to the raw coal samples from B10 seam of -780 m elevation in Huainan coal mine, the MTSS15.04 electro-hydraulic servo testing system is used to carry out the conventional triaxial compression test under high stress. The deformation, strength, parameters and failure characteristics of coal are studied. The results show that： （1） The deviatoric stress-axial strain curves of coal are mainly composed of stages of elastic, yield, post-peak brittle failure or strain softening segment. Among them, the elastic period is longer obviously, and the greater the confining pressure is, the steeper the curve is, the greater the elastic modulus is. But, the yield period is shorter. （2） The post peak brittle failure feature of coal is apparent under uniaxial loading or low confining pressure. As the confining pressure increases, the ductile features start to appear after peak. The higher the confining pressure is, the more obvious characteristics of ductility are. When the confining pressurereaches to 50 MPa, the post-peak axial strain almost presents plastic flow pattern. （3） With the increase of confining pressure, the peak axial strain increases in parabolic trend, and the peak lateral strain increases in linear trend. （4） The deviatoric stress-volume strain curve of coal shows dilatancy mechanism under low confining pressure. The lower confining pressure is, the more obvious the dilatancy features shows. In the high confining pressure, the curve from pre-peak to post-peak is always right extend, and presents a continuous shrinkage state. And with the increase of confining pressure, the peak volume strain presents a parabolic increase form, which reflects the shrinkage characteristics significantly. （5） With the increase of confining pressure, the strength of coal increases in linear trend. The strength parameters c, （a are 12.72 MPa, 24.12°, respectively. （6） The failure modes of coal samples are mainly given priority to shear failure, and the rupture angle is in the range of 23°- 35°. With the increase of confining pressure, the rupture angle increases in parabolic trend. The change can be better explained by Mohr strength theory.