高湿环境对白云岩膨胀过程中力学特性影响的宏微观机制
Dolomite′s macro⁃microscopic mechanism of mechanical property deterioration under high⁃humidity conditions
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摘要: 为了探究深部开采后矿柱力学性能受高湿环境的影响规律,对湖南郴州茶山岭煤矿 -850 m白云岩矿柱取心制作标准试样,采用核磁共振(NMR)、扫描电镜(SEM)、电子能谱(EDS)和 X 射线衍射(XRD)对 4 种湿度环境(相对湿度 70%,80%,90%,100%)中 60 d 限制轴向位移的白 云岩孔隙尺寸、微观结构及矿物组分进行跟踪测定,研究吸水速率与孔隙结构的动态响应特征。 结 合室内单、三轴压缩力学试验结果,总结了白云岩吸水膨胀后的强度软化机制。 研究表明:1环境 湿度越高,白云岩的环向应变与轴向膨胀力前期的增速越快,趋于平稳的时间相对靠后,并在膨胀 力达到最大值后,出现明显的应力松弛;2 装置中环境湿度的升高以及湿度作用时间的延长削弱 了白云岩的强度并加剧了变形。 近似现场湿度下(相对湿度 90%),内摩擦角在 60 d 中下降幅度较 为平均,反观黏聚力前后 20 d 变化较小,集中在 20 ~ 40 d 迅速下滑;3 白云岩在吸水前期核磁共振 T2 谱曲线出现双峰现象,且峰值对应弛豫时间持续向右移动,原本致密的层状结构发生开裂,小中 孔隙扩张并连通形成大孔隙。 基于吸水曲线及 T2 谱面积曲线特征,将整个高湿作用过程分为 3 个 阶段:急速吸水、减速吸水和稳定水化阶段;4 高湿环境下白云岩吸水后,由于结合水膜的润滑作 用以及黏土矿物的膨胀效应引起颗粒间胶结能力减弱,劣化其力学指标,最终改变了白云岩的极限 破坏模式。Abstract: To explore the effects of high⁃humidity on the mechanical properties of rock pillars in deep mining,some standard specimens were produced with cores collected from dolomite pillars below - 850 m depth at the Chashanling coal mine. To further study the dynamic response characteristics of water absorption rate and pore struc⁃ ture,the pore size,microstructure and mineral components of dolomite with 60 d limited axial displacement under four high⁃humidity conditions (70%,80%,90%,100% RH) were tracked and measured by nuclear magnetic reso⁃ nance ( NMR ) , scanning electron microscopy ( SEM ) , energy dispersive spectroscopy ( EDS ) and X⁃ray diffraction (XRD). Combined with laboratory results of uniaxial and triaxial compression tests,the strength soften⁃ ing mechanism of dolomite after water swelling was summarized. The results show that 1 higher environmental humid⁃ ity causes faster circumferential strain at the early stage,and it needs more time to be stabilized. A significant stress re⁃ laxation occurs after the expansion force achieves its maximum value. 2 Higher humidity and longer action time weak⁃ en the strength and accelerate the deformation of dolomite. Under a near⁃site humidity condition (90% RH),the inter⁃ nal friction angle declines more evenly over 60 d. In contrast,the cohesion changes less at the first and last 20 d and drops rapidly between 20~40 d.3 Double peaks appear in NMR T2 spectrum curve at the beginning of water ab⁃ sorption. The relaxation time of peak value continuously moves to the right. The originally compact layered struc⁃ ture develops cracks and small mesopores expand and connect to form large pores. According to the characteristics of water absorption curve and T2 spectrum area curve,a high⁃humidity condition exerts some influences in three stages: rapid water absorption, slow water absorption and stable hydration. 4 After dolomite absorbs water under a high⁃humidity condition,the mechanical parameters are weakened by the lubricating effect of bound water film and the swelling effect of minerals,which finally changes the limited failure mode of the dolomite.