富水环境下板岩膨胀过程宏-细-微观机制研究

Macro-meso-micro mechanisms of rich-water slate in the swelling process

为研究富水板岩宏观膨胀过程与微细观演化的关联性,从湖北省竹溪县板岩膨胀性问题出发,通过侧向约束下的膨胀率试验及恒体积条件下的膨胀力试验,探究板岩膨胀的宏观变形规律;利用X射线衍射(XRD)试验来确定岩样矿物的类型,通过扫描电子显微镜(SEM)试验观察板岩吸水后的微观结构及形态变化,分析板岩吸水膨胀的内部因素及微观结构演化规律;通过核磁共振(NMR)试验,得到板岩的T2谱分布,探究板岩泥化膨胀过程的细观机制。研究结果表明:在富水环境下,板岩的膨胀率以及膨胀力前期增速比较大,随着时间的推移,膨胀速率趋缓,最终膨胀率趋于定值,而膨胀力达到最大值后,呈现微幅降低的过程;随着浸泡时间的延长,黏土矿物含量总体呈现递增趋势,溶液趋于弱碱性;天然板岩T2谱分布呈现双峰形状,且以小孔隙为主,遇水后呈现三峰分布,内部开始出现大孔隙,孔隙总体积表现为先增后减,在浸泡2h时孔隙体积最大;吸水后板岩矿物颗粒开始膨胀,引起颗粒体积增大,颗粒间接触力增大,在宏观上表现为应力、应变张量的增大,解释了板岩膨胀变形与膨胀力产生的内部缘由。黏土矿物的微量溶解,使得膨胀应力微减,解释了达到最大膨胀应力后的微降现象。以宏观-细观-微观尺度研究板岩的膨胀特性,以期建立板岩宏观膨胀过程与微细观结构之间的关系,可为膨胀岩膨胀机制研究提供理论支持。

In order to research the relationship between macro-expansion process and micro-evolution of water-rich slate,the expansion rate test under lateral restraint and the expansion force test under constant volume condition of slate taken from Zhuxi county,Hubei province,were performed to investigate macro swelling deformation of slate. The types of sample minerals were determined by X-ray diffraction(XRD),the microstructure of samples after water absorption was observed by scanning electron microscope(SEM) for investigate the internal factors of the expansion of slate after water absorption and the evolution law of the micro-structure,and the T2 spectrum distribution of slate was obtained by NMR for studying the micro-mechanism of mud expansion process of slate. The results show that under the rich-water environment,the expansion rate of slate increases rapidly in the early stage,then tenderly and tends to be stable,while the expansion force shows a slightly decreasing process after quickly increasing up to the maximum. With the prolongation of soaking time,the content of clay minerals in slate increases and the solution tends to be weak alkaline as a whole. The T2 spectrum of natural slate shows double peaks and mainly consists of small pores. After water immersion,the T2 spectrum shows three peaks and the internal macro-pores appear. The total pore volume increases first and then decreases with a maximum value at 2 h of immersion. After water absorption,mineral particles of slate begin to expand,resulting in the increases of the particle volume and the contact force between particles,and consequently,stress and strain tensors increase macroscopically,which explains the internal causes of expansion deformation and expansion force of slate. The slight dissolution of clay minerals makes the expansive stress decrease slightly,which explains the phenomenon of the slight drop of the expansive stress after reaching the maximum. This study can provide a theoretical support for the study of swelling mechanisms of expansive rock.