基于岩石CT扫描的冻融作用对花岗岩细观结构及力学强度影响研究  

Mesostructure and strength characteristics of granite under freeze-thaw cycles based on CT scanning

作　　者：侯圣山[1,2,3] 何箫 孟宪森 陈亮 冯振[1,2,3] 刘明学 李昂[1,2,3] 郭长宝 吉锋 HOU Shengshan;HE Xiao;MENG Xiansen;CHEN Liang;FENG Zhen;LIU Mingxue;LI Ang;GUO Changbao;JI Feng(Chinese Institute of Geological and Environmental Monitoring,Beijing 100081,China;Observation and Research Station of Geological Hazard in Ya’an,Sichuan,Ministry of Natural Resources,Ya’an 625099,Sichuan,China;Technology Innovation Center for Geohazard Monitoring and Risk Early Warning,Ministry of Natural Resources,Beijing 100081,China;State Key Laboratory of Geological Disaster Prevention and Geoenvironmental Protection,Chengdu 610059,Sichuan,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China)

机构地区：[1]中国地质环境监测院,北京100081 [2]自然资源部四川雅安地质灾害野外科学观测研究站,四川雅安625099 [3]自然资源部地质灾害智能监测与风险预警工程技术创新中心,北京100081 [4]成都理工大学地质灾害防治与地质环境保护国家重点实验室,四川成都610059 [5]中国地质科学院地质力学研究所,北京100081

出　　处：《地质力学学报》2024年第3期462-472,共11页Journal of Geomechanics

基　　金：国家重点研发计划项目(2021YFC3000505,2021YFB2301304);中国地质调查局地质调查项目(DD20221748)。

摘　　要：近年来随着西部地区的基础工程建设数量及规模不断增加,西部高原地区的季节性冻融循环效应的影响也随之增强,开展冻融循环作用下岩石细观特性及强度劣化性质研究对指导西部寒区基础工程建设至关重要。首先在偏光显微镜下对岩石薄片进行观察,获取岩石的矿物成分和微结构;接着利用CT扫描技术,对冻融后的花岗岩进行扫描,对扫描图层利用阈值分割进行二值化处理,堆叠得到样品内外结构的高分辨3D数据及影像;结合分形理论计算图像计盒维数并由此对图像复杂度做出量化判断,由此对冻融循环对花岗岩内部结构演化分布特点进行分析;进而揭示其强度演化规律,探究结构演化与强度之间的关系。偏光显微镜下,岩石呈块状构造,具有似斑状粗粒不等粒花岗结构,局部见交代蠕虫结构。似斑晶矿物主要为碱性长石;其他矿物粒径0.25~4.0 mm为主,矿物成分主要为石英、斜长石、碱性长石,次要矿物为黑云母、绿帘石,副矿物有磷灰石、锆石、黄铁矿等,镜下鉴定为似斑状粗粒不等粒黑云二长花岗岩。CT扫描显示,冻融循环效应在影响花岗岩细观结构时,会导致花岗岩内部孔隙率的整体上升,但岩石渗透性变化不大,岩石渗透率仅上升0.003×10^(-3)μm^(2);内部孔隙发育不均匀,试样整体结构改变以萌生较多新的微孔隙为主。冻融循环后岩石内部结构复杂度有所下降,但岩石整体完整性仍然较好,分形维数仍保持在较高水平。分形研究显示,20次冻融循环并未导致花岗岩的结构复杂度发生较大变化,同时试样整体力学特性出现下降,黏性增加以及长期强度出现较大幅度的衰减,进入蠕变试验阶段的应变阈值提高。在评价此类原生结构较致密的岩石的安全性时,仅从结构上进行考量与实际情况往往会出现偏差,应结合必要的强度指标综合评估。岩石在经历冻融循环后,在强度[Objective]With the rapid increase in construction projects in the western regions in recent years,the impact of seasonal freeze-thaw cycles in the high-altitude areas of western China has become more pronounced.Conducting research on the microscopic characteristics and strength degradation properties of rocks under freeze-thaw cycles is crucial for guiding engineering construction in these cold,high-altitude regions.[Methods]To study the influence of freeze-thaw cycles on rock structure and mechanical properties,we collected diorite samples from a tunnel in the Kangding area and examined the effects of freeze-thaw cycles on their microstructure and mechanical characteristics.Firstly,thin rock sections were observed under a polarizing microscope to obtain mineral compositions and microstructures.Then,CT scanning technology was used to scan the granite samples after freeze-thaw cycles,and the scanned layers were binarized using threshold segmentation.The scanning images of different layers were binarized using threshold segmentation,and highresolution 3D data and images of the internal and external structures of the samples were obtained by stacking the binary image layers.Fractal theory was applied to calculate the box-counting dimension of the images and quantitatively assess their complexity.This analysis allowed us to examine the evolution and distribution characteristics of the internal structure of granite under freeze-thaw cycles.[Results]Under a polarizing microscope,the rock exhibits a block-like structure with a patchy,coarse-grained,and unequal-grained granite texture,with locally visible metasomatic worm structures.The main phenocryst minerals are alkaline feldspar.Other minerals range in size from 0.25 to 4.0 mm and primarily include quartz,plagioclase,and alkaline feldspar.Secondary minerals include biotite and epidote,while accessory minerals comprise apatite,zircon,and pyrite.Microscopically,the rock is identified as porphyritic,coarse-grained,and unequal-grained biotite diorite granite.Freeze-thaw

关 键 词：冻融循环 阈值分割 CT模型 分形维数 结构演化 长期强度 

分 类 号：P642[天文地球—工程地质学]