基于CT成像技术的含方解石脉灰岩溶蚀作用微观结构和变化规律研究

    STUDY ON MICROSTRUCTURE AND CHANGE RULE OF CALCITE BEARING VEIN LIMESTONE DISSOLUTION BASED ON CT IMAGING TECHNOLOGY

    • 摘要: 为研究溶蚀作用下含方解石脉灰岩孔隙的演变规律及控制作用,文章选取武汉地区8个岩溶条带的6种不同结构的含方解石脉灰岩进行取样并开展溶蚀试验,同时结合CT成像对试验前后岩石的溶蚀特征及孔隙结构进行对比分析。研究结果表明:(1)含方解石脉中-细粒结晶斑状灰岩溶蚀前后的质量、pH值、电导率变化速率最大,溶蚀后孔隙体积增加显著,孔隙结构间的连通性明显改善;(2)含方解石脉泥晶、微晶结构的灰岩经溶蚀后小孔隙占比减少,中孔隙、大孔隙占比明显增加,当粒径增大至粉晶结构时情况与之相反。其中:微晶含方解石脉灰岩的孔喉长度和等效直径更容易发展;(3)含方解石脉灰岩整体分形维数与其孔隙和裂隙分形维数对比明显偏大,裂缝的分形维数高于孔隙的分形维数。泥晶结构的含方解石脉灰岩的分形维数最低,含方解石细脉中-细晶白云质灰岩的分形维数最大,在溶蚀后岩样各自裂隙、孔隙分形维数上下浮动变化具有随机性;(4)含方解石脉中-细粒结晶斑状、泥晶、细晶白云状结构的灰岩,表面渗透率依次减少。表面渗透率的计算值总体上与实测值的演化规律相符,说明基于μ-CT扫描结果的渗流模拟可作为评价岩体渗透特性的一种辅助手段。研究结果对含方解石脉灰岩差异性岩溶作用机理及岩溶发育规律的认识有一定指导意义。

       

      Abstract: For the purpose of conducting a dissolution test,samples of six distinct calcite vein limestone structures from eight karst strips in the Wuhan region were chosen to examine the pore evolution law and control impact of the limestone during dissolution. Meanwhile,CT imaging was used to examine the dissolving properties and pore structure of the rocks before and after the test. The findings demonstrate that: (1)The medium-fine crystalline porphyritic limestone has the highest mass,pH value,and electrical conductivity both before and after dissolution; the pore volume rises noticeably after breakdown,and there is a clear improvement in the connection between pore structures; (2)In the calcite vein micrite and microcrystalline limestone,the proportion of tiny holes diminishes while the proportion of medium and large pores greatly rises during dissolution. When the particle size reaches the powder crystal structure,the situation is the opposite. The microcrystalline calcite vein limestone's pore throat length and comparable diameter are the easiest to form among them; (3)Calcite vein limestone has a far larger total fractal dimension than its pores and fractures combined,with fractures having a higher fractal dimension than pores. The calcite vein limestone with micrite structure has the lowest fractal dimension,whereas the calcite fine dolomite limestone has the largest fractal size. Following disintegration,the fractal dimension of the rock samples' pores and fractures varies at random; (4)Calcite veins with medium-fine grained crystalline porphyritic,micrite,and fine-grained dolomitic features gradually lose their surface permeability. The evolution law of the measured values and the estimated surface permeability values are typically in agreement,suggesting that the seepage simulation based on the μ-CT scanning data may be utilized as a backup method to assess the permeability properties of the rock mass. The study's findings can be used to better understand the various karst mechanisms and karst growth laws of limestone with calcite veins.

       

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