基于特征应力的准静态三轴煤岩脆性特征分析

doi:10.13722/j.cnki.jrme.2021.0278

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摘要依托MTS815岩石力学试验系统开展准静态应变率下三轴煤岩压缩试验，分析煤岩变形破坏特征及能量演化规律，利用能量耗散理论确定损伤应力，并提出一种基于不同特征应力且能反映煤岩峰前、峰后力学行为的脆性指标，以分析不同应变率、不同围压作用下煤岩的脆性变化规律。研究表明：准静态三轴煤岩应力–应变曲线存在明显的阶段性特征，随围压升高、应变率降低，峰后应力跌落量减小，破坏形式由张拉破坏向剪切破坏过渡，煤岩的脆性破坏特征减弱。考虑到能量耗散导致煤岩内部出现不可逆损伤，定义耗散能与总应变能的比值为耗散能率，确定耗散能率曲线的极小值点为损伤应力点。综合考虑峰前裂纹扩展程度与峰后应力跌落程度，结合损伤应力、峰值应力与残余应力建立准静态三轴煤岩的脆性指标Bstress。随围压升高、应变率降低，Bstress减小，说明煤岩脆性减弱。通过与其他脆性指标对比分析发现Bstress更能体现出煤岩脆性受应变率的促进与围压的抑制作用。利用变异系数进一步分析同一组平行试验下各脆性指标的离散程度，发现Bstress的离散性最小，在准静态应变率下表征三轴煤岩的脆性特征更为合理。

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	刘晓辉1
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	郑钰2
	郝齐钧2
	桂欣2
	薛洋2

关键词 ：岩石力学, 准静态应变率, 三轴煤岩, 脆性, 耗散能, 特征应力

Abstract：The triaxial compression tests of coal rock under quasi-static strain rate were carried out by using MTS815 test system，and the failure characteristics and energy evolution law of coal rock were analyzed. By using energy dissipation theory to determine the damage stress，a brittleness index reflecting the pre/post-peak mechanical behavior was established based on characteristic stress to analyze the brittleness traits of coal rock under different strain rates and confining pressures. The results show that stress-strain curves of quasi-static triaxial coal rock have obvious stage characteristics. As the confining pressure increases and the strain rate decreases，the post-peak stress drop declines，failure mode transitions from tensile failure to shear failure，and the brittle failure characteristics of coal rock are gradually weakened. According to the irreversible damage in coal rock due to energy dissipation，the dissipation energy rate is defined as the ratio of the dissipation energy to the total strain energy，and the minimum of the curve of the dissipation energy rate is determined as the damage stress point. Comprehensively considering the degree of crack propagation in pre-peak and stress drop in post-peak，a brittleness index Bstress of quasi-static triaxial coal rock is established with the combination of the damage stress，the peak stress and the residual stress. Bstress decreases as the confining pressure increases and the strain rate decreases，indicating that the brittleness of coal rock is weakened. Comparing with other brittleness indexes，it is found that Bstress can better depict that the brittleness of coal rock is promoted by the strain rate and restrained by the confining pressure. Further analysis of the dispersion degree of each brittle index under the same group of parallel tests is carried out by using the coefficient of variation，finding that the dispersion of Bstress is minimal and it is more reasonable to characterize the brittleness of triaxial coal rock under quasi-static strain rate.

Key words： rock mechanics')" href="#">

rock mechanics quasi-static strain rate triaxial coal rock brittleness dissipation energy characteristic stress

引用本文:

刘晓辉1，2，郑钰2，郝齐钧2，桂欣2，薛洋2. 基于特征应力的准静态三轴煤岩脆性特征分析[J]. 岩石力学与工程学报, 2021, 40(12): 2454-2465.
LIU Xiaohui1，2，ZHENG Yu2，HAO Qijun2，GUI Xin2，XUE Yang2. Brittleness characteristics of quasi-static triaxial coal rock based on characteristic stress. , 2021, 40(12): 2454-2465.

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http://rockmech.whrsm.ac.cn/CN/10.13722/j.cnki.jrme.2021.0278 或 http://rockmech.whrsm.ac.cn/CN/Y2021/V40/I12/2454

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