基于CT扫描的三维重构煤体加载损伤演化特征及尺寸效应

Damage evolution characteristics of 3D-reconstructed coal during loading and its size effects based on CT scanning

煤体是一种包含孔隙结构和矿物成分的多孔材料,具有明显的各向异性和尺寸效应。为研究煤体各向异性及尺寸效应对破坏特征的影响,本文提出了一种基于CT扫描、核磁共振和X衍射等技术手段的煤样内部孔隙、矿物成分表征和三维重构模拟方法。在此基础上,反演实验室单轴压缩获得了三维重构模型煤基质和矿物成分的模拟参数,进一步模拟分析了不同宽高比煤体的强度损伤特征。模拟结果表明:①在加载过程中,塑性区首先在孔隙和矿物成分周边逐渐向外扩展连通。在空间分布上,塑性区前期由加载端垂直向内部扩展,后期转变为由四周水平向内部扩展,最终模型破坏的非塑性区形成“双圆台结构体”。②随着宽高比的增加,煤样的抗压强度(p)、达到屈服强度时的应变(ζ)以及弹性模量(K)均会增加,其中ζ和K呈线性增加,而p增幅逐渐减小。③在煤样单轴加载过程中总能量和弹性能呈指数增加,耗散能呈线性增加。随着宽高比增加,煤体内积聚的弹性能增加,破坏时释放的能量增大,更容易诱发动力冲击相关灾害。研究结果为冲击矿压地区区段煤柱尺寸的合理选择提供参考。

Coal is a porous material containing pore structures and mineral components,exhibiting pronounced anisotropy and size effects.In order to investigate the influence of coal anisotropy and size effects on its failure characteristics,this paper proposes a simulation method for characterizing and reconstructing three-dimensionally the internal pores and mineral components of coal samples based on CT scanning,nuclear magnetic resonance,and X-ray diffraction.Specifically,we obtained simulation parameters of three-dimensional reconstruction models of coal matrix and mineral components through inverse laboratory uniaxial compression experiments,while simulated and analyzed the strength damage characteristics of coal bodies with different aspect ratios.The simulation results show that:①During the loading process,the plastic zone first gradually expands and connects outward around the pores and mineral components.In terms of spatial distribution,the plastic zone expands vertically from the loading end to the interior in the early stage,and in the later stage,it expands horizontally from the surroundings to the interior.After the model is damaged,a"double truncated cone structure"is formed in the non-plastic zone.②The increase of aspect ratio leads to an increase in the compressive strength(p)of coal samples,the strain(ζ)at yielding strength,and the elastic modulus(K),among whichζand K increase linearly,while the margin of increase in p gradually decreases.③The total energy and elastic energy of coal sample loading increase exponentially,while the dissipated energy increases linearly.The increase of aspect ratio leads to an increase both in the accumulated elastic energy in the coal body and in the released energy during failure,which easily induce dynamic impact-related disasters.This study provide references for the reasonable selection of coal pillar size in impact mine pressure area.