硬脆岩石的微观颗粒模型及其卸荷岩爆效应研究

A MICRO PARTICLE MODEL FOR HARD BRITTLE ROCK AND THE EFFECT OF UNLOADING ROCK BURST

为准确反映硬脆岩石的力学特性并对其卸荷岩爆效应进行合理模拟,从微观层面建立了硬脆岩石的力学模型。首先依据花岗岩岩样的衍射测试确定了模拟岩样的微观结构,其次从能量发展和应力–应变2个角度确定了硬脆特性的评价指标,借助评价指标进行岩样的颗粒效应分析和力学性能调控,进而构建了一种反映岩石硬脆特性的微观颗粒模型"可视构架"(基于现有岩样结构,颗粒与黏结参数需保持的趋势和量值限制)。应用模型并采用颗粒流程序PFC3D对不同围压三轴卸荷下的岩爆效应进行模拟分析,结果表明:岩样的低围压卸荷与高围压卸荷都体现出以张拉性质为主导的黏结断裂,但高围压卸荷比低围压卸荷有更高的张拉断裂比重,体现出更明显的脆性破裂性质,应力跌落曲线表现得更为陡直;低围压卸荷下颗粒动能在破裂过程中均有所发展,岩爆效应体现出"持续型"特点,高围压卸荷下颗粒动能则表现出明显的差异性,岩爆效应体现出"爆发型"特点。

A bonding particle model for hard brittle rock has been established to simulate the effect of rock burst.To make the microscopic model reflecting properties of hardness and brittleness,the following steps were used.Firstly,the microstructure of simulated rock samples was measured with the X-ray diffraction testing for granite rock. Secondly, the mechanical properties of the rock samples were analyzed, supported with the evaluation indicators of hardness and brittleness(indicators were determined in terms of the energy and stress-strain characteristics). Finally, a visual framework of the bonding particle model(depending on the tendency and magnitude limitation of the existed microstructure, the parameters of particles and bonds) representing the properties of hardness and brittleness was established. The model and the particle flow code(PFC3D) were used to simulate the triaxial unloading test and to analyze the effect of rock burst. The fractures are found to be mainly tensile in the unloading tests with the low and high confining pressures. Bigger proportion of tensile fractures and larger stress dropping(more brittle) occurs under the high confining pressure than under the low confining pressure.The kinetic energy of particles under the low confining pressure develops uniformly in the whole fracturing process of simulated sample, and the rock burst is a continuous type. However, the kinetic energy of particles under the high confining pressure developed non-uniformly,and the rock burst occurred suddenly and explosively.