基于数字图像技术的结构裂缝参数分析

基于数字图象处理技术,提取并分析了含结构裂缝照片中与裂缝分布有关的数字特征参数.首先考虑拍摄环境条件(如光线强度等),通过对灰度图像设定适当阈值来区分图像中的裂缝与图像背景,获得了相应二值图像;然后结合形态学膨胀与腐蚀技术,消除二值图像中的噪点,使用边缘检测技术提取裂缝的边缘图像;进而得到裂缝的面积、长度、平均宽度、宽度最大值、宽度最小值以及记盒维数等数字特征参数.这一方法为已有建筑物结构裂缝的确认与分析提供了一条新的途径.     

内蒙古维拉斯托锡多金属矿床流体包裹体特征及其地质意义

维拉斯托矿床位于大兴安岭南段西坡有色金属成矿带,包括花岗岩型和石英脉型锡钨矿、脉状铜锌矿,其形成与深部碱长花岗岩密切相关。通过岩相学、显微测温、激光拉曼等手段对维拉斯托碱长花岗岩、云英岩、锡石闪锌矿石英脉3种地质体中熔融、熔流以及流体包裹体特征进行研究。以上3种地质体中包裹体类型由以熔融包裹体为主—以熔流包裹体为主—以气液包裹体为主渐变;熔融包裹体的固相成分以钠长石为主,少量白云母和萤石,熔流包裹体的固相成分为黄玉;由云英岩到锡石闪锌矿石英脉,均一温度降低,盐度略有降低,变化具有继承性。维拉斯托成矿流体经历了岩浆到热液的连续演化过程,晚期形成浆液过渡态流体,成矿作用始于岩浆晚期,浆液过渡态流体与锡成矿作用具有直接的联系。     

流体包裹体法在岩体滑坡周界预测中的应用

岩体滑坡是岩体变形与破坏状态达到一定程度的结果,岩体中流体包裹体参数及其变化是反映这一状态变化的重要微观指标,研究这些参数及其变化可以确定岩体滑坡的滑动周界。以浙江省湖州市白鹤岭滑坡为例,分析16个测试样本的流体包裹体迹面特征参数(包括张开度、粗糙度系数和分布密度)和包裹体热动力学参数(包括水溶液包裹体和CO2-H2O包裹体的均一温度和流体密度),使用聚类分析与对应分析对反映流体包裹体迹面特征的样本、指标和滑坡周界的相互关系进行分析,提出分类标准和聚类方法的建议。结果表明,16个测试样本分为3类比较合适,3种样本类型与稳定区、滑坡周界、滑动区基本一致,样本、指标和滑坡周界之间具有较好的对应关系。在此基础上,提出确定岩体滑坡周界的一种新方法:流体包裹体方法。这一方法将为岩体滑坡的分析与预测提供一条具有良好前景的新方法。     

Effects of local rock heterogeneities on the hydromechanics of fractured rocks using a digital-image-based technique

A digital-image-based (DIB) finite element approach is developed based on the numerical code rock failure process analysis (RFPA) to characterize micro-scale rock heterogeneity, and to understand the impact of micro-scale rock heterogeneity on the macro-scale hydromechanical response of rocks. The DIB technique incorporates small-scale spatial variability of initial deformation modulus, strength and permeability directly into a coupled hydromechanical model. Variability in Young's modulus, strength, and permeability is applied by a property map defined from the pixel-scale of a digital image. In the RFPA, mechanical deformation is followed, including the accumulation of damage applied in individual elements, which modifies modulus, strength, and permeability with the intensity of damage. The RFPA simulates progressive failure in fractured rocks, representing both the growth of existing fractures and the formation of new fractures, without having to identify crack tips and their interaction explicitly. In this DIB simulation approach, image voxels are used to give equivalent mechanical and flow properties. These property maps are ported to the model capable of solving directly for the evolving deformation, and fluid flow fields. The model is validated through comparisons of the simulated results with phenomenological observations documented in previous studies. The validated model is then applied to investigate the hydromechanical response of fractured rock characterized by digital image. The model is able to reproduce the spatial evolution of damage in the sample, the coalescence of existing cracks, and the formation of new cracks.     

Monitoring Crack Changes in Concrete Structures

Abstract:   This study proposes a crack-monitoring system to quantify the change of cracks from multitemporal images during the monitoring period. A series of images were taken from an off-the-shelf digital camera. Concrete cracks were extracted from the digital images by employing a series of image-processing techniques. The image coordinates and orientation of same cracks can be changed since the position and direction of the portable camera vary at every exposure time. To monitor the crack changes (width and length), it is critical to transform the image coordinates of cracks extracted from each image into the same object coordinates of the concrete surface. In this study, such a geometric relationship was automatically recovered using the two-dimensional (2D) projective transformation based on the modified iterated Hough transform (MIHT) algorithm, the result of which solved the transformation parameters. To improve the computational operation of MIHT, regions of parameter estimation were also investigated. The developed algorithms were applied to monitor the crack of the concrete specimen. As a result, the change of cracks on the concrete specimen was successfully detected and accurately quantified.     

基于细观结构表征的岩石破裂热–力耦合模型及应用

 岩石热破裂的研究只有考虑各种矿物组分造成的岩石的非均匀性,才能更客观地反映岩石热破裂的本质。利用数字图像处理技术数字化表征岩石内部矿物颗粒的几何形态,充分考虑岩石真实的细观结构,结合细观损伤力学和热弹性理论,建立能更客观的分析岩石热–力耦合作用下破裂过程的数值模型。以花岗岩为例,运用数值模型研究花岗岩在温度和压缩荷载共同作用下的力学行为和破裂过程。研究结果表明,温度对岩石的力学性质和破裂演化过程影响显著,热破裂裂纹多发生在矿物颗粒边界处,并沿颗粒边界扩展,局部会形成闭合多边形,其热破裂演化过程与试验结果基本相符,从而验证了数值模型的合理性和有效性,该数值模型为细观尺度定量研究岩石热破裂提供一种新的方法。     

基于数字图像相关技术的土体干缩开裂过程研究

在干燥条件下,土体极易蒸发失水收缩产生开裂,深入研究土体干缩开裂过程对准确掌握干旱气候环境中的土体工程性质响应特性具有重要意义。通过对黏性土开展室内干燥试验,采用数码相机实时记录土体表面裂隙的动态发育过程,结合数字图像相关技术,获取土体收缩开裂全过程。结果表明:①裂隙通常在土体表面张拉应力集中处产生,裂隙产生后周围应力场得到迅速释放并发生重排,且裂隙间倾向于成直角相交;②土体表面的位移场和应变场可以有效反映土体收缩开裂过程中的动态特征,能为分析和预测裂隙的演化过程提供重要参考信息;③土体被裂隙分割成不同的块区,每个块区在收缩过程中都存在收缩中心现象,且各块区的收缩中心位置会随时间而变化;④数字图像相关技术能有效识别不同图像之间的灰度特征值,能在完全不扰动土样的条件下准确获取土体表面干缩变形信息的时空演化特征,为研究土体干缩开裂动态过程及机理提供了优越的技术手段,具有较好的推广价值。     

层状裂隙岩体蠕变柔量估计的合理方法

基于Taylor模型方法和粘弹性断裂力学理论，推导了层状裂隙岩体的单轴、剪切以及体积蠕变柔量，并合理考虑了裂隙相互作用效应的影响，分析了层状裂隙岩体单轴蠕变和剪切蠕变的各向异性。计算分析指出，裂隙岩体的单轴蠕变柔量随裂隙密度参数的增加而增大，随裂隙倾角的增加而减小。考虑裂隙相互作用效应时，层状裂隙岩体的蠕变柔量明显大于不考虑裂隙相互作用的情况。该方法为通过室内岩石流变实验了解实际工程中裂隙岩体的蠕变特性提供了一种可能。     

基于计算机视觉技术的结构表面裂缝检测方法研究

计算机视觉技术用于混凝土结构表面裂缝检测,具有现场检测方便、效率高、客观性强的特点,但图像数据分析是该技术的核心,其中裂缝提取与定量测量较为复杂。为提高裂缝图像处理效率和准确率,将深度学习和数字图像处理技术相结合,提出一种裂缝检测方法。建立基于深度卷积神经网络的裂缝识别模型,在图像上自动定位裂缝并结合图像局域阈值分割方法提取裂缝。在裂缝宽度定量测量方面,采用双边滤波算法和三段线性变换对裂缝图像进行预处理,提高了裂缝边缘识别的精确度。通过改进边缘梯度法,实现裂缝最大宽度的定位和裂缝最大宽度的自动获取。该研究为全自动识别裂缝图像及高精度测量裂缝宽度提供了一种解决方法。     

三轴应力下致密砂岩的裂纹发育特征与能量机制

 开展致密砂岩三轴压缩试验及CT扫描试验,获得不同围压作用下岩石破坏裂纹的几何形态CT图像;利用图像处理、统计学等方法构建破坏裂纹形态的三维空间模型,分析不同围压对破坏裂纹几何形态和分布特征的影响规律,基于能量理论揭示不同三轴应力下岩石破坏时裂纹扩展的能量机制。研究表明：围压对岩石破坏裂纹的形态、数量和空间分布特征有很大的影响。当围压较低时,破坏裂纹数量众多、形态复杂,最终形成主裂纹和次生裂纹交叉分布的裂纹网络结构;围压较高时,最终形成的破坏主裂纹数量减少,次生裂纹消失,形态复杂的裂纹网络被近似直线的破坏裂纹所取代;围压对岩石破坏裂纹扩展的能量耗散和能量释放特征有显著的影响。随着围压的增加,单位体积内的可释放弹性应变能线性增加,而耗散能则呈线性递减趋势。低围压时破坏裂纹的耗散能较大,从而产生几何形态复杂、数量众多的微裂纹。而高围压时的耗散能较少,产生的破坏裂纹数量减少,几何形态趋于简单化、规则化。     

Sub-critical crack growth in anisotropic rock

In this study, subcritical crack growth in granite was investigated experimentally using the double torsion (DT) test. The orthorhombic elastic properties of granite, caused by the preferred orientation of pre-existing microcracks, were used to estimate the crack velocities and the stress intensity factors. The results showed that the crack velocity in granite varied depending on its direction of propagation. The fastest crack velocities for a given water vapor pressure were obtained when the crack propagated in the direction parallel to the plane in which the crack density of the pre-existing microcracks was the highest. Hence, subcritical crack growth in granite is affected by pre-existing microcracks. It was shown that the crack velocity was high when the water vapor pressure was high. From the results obtained under different temperatures and water vapor pressures, values of the activation energy for subcritical crack growth were estimated. The crack velocity under any given temperature, water vapor pressure, and stress intensity factor can be predicted theoretically if the activation energy is accurately estimated. The activation energy in granite is higher than that in glass. Cracks propagate in a straight line in glass, whereas they do not form a straight line in rocks due to the heterogeneity. The total length and surface area of cracks in rocks are therefore greater than those of straight cracks in glass. The larger activation energies in rocks are due to their heterogeneity.     

基于摄影法的红黏土裂隙试验研究

准确提取红黏土裂隙特征,有助于进一步研究裂隙对红黏土工程性质的影响。本文以桂林红黏土试样为试验研究对象,获取红黏土表面裂隙数字图像后,通过比对不同方法,发现直方图阈值法适用于红黏土的裂隙图像分割。通过去除杂点、填充细小孔洞,将裂隙数字图像转化为二值图像,最后进行骨骼化和消刺处理,可得裂隙骨骼图像。研究发现试样在第5次干湿循环后裂隙发育均已趋稳定;初始含水率为25%的试样在干湿循环作用下发育出线状裂隙;初始含水率为28%的试样则发育出网状裂隙;干湿循环次数与裂隙率和裂隙总长度具有良好的相关性,可用二次函数拟合。     

压剪应力条件下砂岩双面剪切细观开裂扩展演化特性试验研究

 利用自主研发的煤岩双面剪切细观开裂演化过程试验装置,通过开展不同法向应力条件下的剪切试验,借助声发射技术及图像处理技术,对细观开裂扩展过程、细观开裂扩展空间分布进行深入探究。研究结果表明：对于压剪应力条件下的双面剪切试验,加载过程中的大部分阶段,试件表面损伤不明显,表面裂纹出现在峰值剪应力之前;当剪应力达到峰值前,Hit率有一个急剧增加的过程,说明砂岩内部已有裂纹产生,而试件表面并无明显变化,一段时间后才在表面观测到细小裂纹,推测裂纹由内向外扩展;试件发生宏观破坏后,左右两侧裂纹呈八字形或梯形分布,由于竖向剪切力引起的岩体内部剪切破坏占主导作用且砂岩内部晶粒间存在一定的几何物理性质差异,主裂纹基本沿预定剪切面扩展的同时表现出开裂扩展的不规则性;裂纹多在石英、长石等矿物颗粒的边缘即砂岩中相对薄弱的环节产生,随着应力水平的增加,裂纹也会穿过矿物颗粒形成穿晶破裂,这种现象多在石英颗粒中出现,这与其特有的微结构特征有关。     

Automated image processing technique for detecting and analysing concrete surface cracks

In the present work, an image processing technique that automatically detects and analyses cracks in the digital image of concrete surfaces is proposed. The image processing technique automates the measurement of crack characteristics including the width, length, orientation and crack pattern. In the proposed technique, a morphological technique was applied to correct the non-uniform brightness of the background, and enhanced binarisation and shape analysis were used to improve the detection performance; furthermore, detailed algorithms to calculate the crack width, length, orientation and an artificial neural network to recognise crack patterns including horizontal, vertical, diagonal (?45°), diagonal (+45°), and random cracks are proposed. An image processing program was developed for the proposed algorithm and a series of experimental and analytical investigations were performed to assess the validity of the algorithm. Then, the crack characteristics measured using the proposed technique were compared with those obtained using a conventional technique. The test results showed that the crack characteristics can be accurately measured and analysed using the proposed technique.     

岩石裂隙组构的定量测定

裂隙组构是用张量确定岩石内部裂隙几何分布的常用方法。基于体视学原理描述组构的理论框架,提出定量测定岩石裂隙组构的方法。该方法采用归一化思想定义裂隙张量,张量的迹恒等于1极大方便了裂隙组构的测定。用测试线测定岩石的平面裂隙张量,用该张量偏张量的第二、第三不变量定义幅值参量和分量角度,定义的2个标量分别确定裂隙各向异性的大小和方向,用这2个量就可以描述平面裂隙的分布规律。用正交面中任意2个幅值参量即可唯一确定三维正交各向异性裂隙张量。随裂隙分布几何关系变化,正交各向异性自然退化为横观各向同性和各向同性的形式。煤岩CT试验结果的验证表明,该张量能够较好描述裂隙的平面分布特点。     

结构表面裂缝数字图像法识别研究综述与前景展望

裂缝反映结构受力状态与安全性、耐久性,是结构现场安全性检测监测以及结构模型试验研究的重要指标之一。现有的人工裂缝识别技术难以满足工程现场与实验室需求,操作中存在测不准、高空多、效率低、记不全等缺点。相比之下,采用数字图像法进行结构表面裂缝识别,具有便捷、自动、定量、准确等优势。文章对结构表面裂缝数字图像法识别研究进行系统综述,对裂缝识别中图像预处理、裂缝识别与提取、裂缝参数计算等重要环节的常见算法进行讨论,阐述采用多视角几何三维重建方法实现裂缝成像修正与拼接、裂缝表达输出的原理与流程,结合实桥案例报道了基于无人机平台的裂缝识别研究与应用,讨论国内首部数字图像法检测规程《工程结构数字图像法检测技术规程》征求意见稿中裂缝检测的相关规定。最后,对结构表面裂缝数字图像法识别研究进行前景展望。     

流体包裹体在工程地质与水文地质中的应用

运用一定的研究方法,对场区内的流体包裹体进行了分析,研究了岩体断裂性质,确定了工程地质体构造变形性质和期次,探索了工程地质体中地应力场的分布规律,并对隐伏断层及活动断层进行了判别,可为水文地质工作提供有益的帮助。     

水作用下岩体断裂强度探讨

分析了裂纹岩体中水压力的作用及类型。在探讨静水压力、动水压力及水化学损伤对裂纹尖端应力强度因子的基础上，推导给出了考虑水压力和水化学损伤作用等不同条件下的含闭合或张开裂纹的岩体断裂强度新准则，并得出：水对含结构面(裂纹或节理)岩体的断裂力学效应的作用包括直接与间接两方面，直接作用来源于裂纹中的静水压力或动水压力：间接作用来源于水对裂纹面上的剪切强度(粘聚力与内摩擦角)的损伤。水对岩体断裂强度的作用，对于裂纹是否闭合，在新准则中有不同的表达式。     

Beamlet Transform‐Based Technique for Pavement Crack Detection and Classification

Abstract: This article presents a Beamlet transform‐based approach to automatically detect and classify pavement cracks in digital images. The proposed method uses a pavement distress image enhancement algorithm to correct the nonuniform background illumination by calculating the multiplicative factors that eliminate the background lighting variation. To extract linear features such as surface cracks from the pavement images, the image is partitioned into small windows and a Beamlet transform‐based algorithm is applied. The crack segments are then linked together and classified into four types: vertical, horizontal, transversal, and block. Simulation results show that the method is effective and robust in the extraction of cracks on a variety of pavement images.     

Theoretical and numerical studies of crack initiation and propagation in rock masses under freezing pressure and far-field stress

Water-bearing rocks exposed to freezing temperature can be subjected to freezeethaw cycles leading tocrack initiation and propagation, which are the main causes of frost damage to rocks. Based on theGriffith theory of brittle fracture mechanics, the crack initiation criterion, propagation direction, andcrack length under freezing pressure and far-field stress are analyzed. Furthermore, a calculation methodis proposed for the stress intensity factor （SIF） of the crack tip under non-uniformly distributed freezingpressure. The formulae for the crack/fracture propagation direction and length of the wing crack underfreezing pressure are obtained, and the mechanism for coalescence of adjacent cracks is investigated.In addition, the necessary conditions for different coalescence modes of cracks are studied. Using thetopology theory, a new algorithm for frost crack propagation is proposed, which has the capability todefine the crack growth path and identify and update the cracked elements. A model that incorporatesmultiple cracks is built by ANSYS and then imported into FLAC3D. The SIFs are then calculated using aFISH procedure, and the growth path of the freezing cracks after several calculation steps is demonstratedusing the new algorithm. The proposed method can be applied to rocks containing fillings such asdetritus and slurry.
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