基于数字图像的盾构隧道衬砌裂缝病害诊断

Diagnosis of structural cracks of shield tunnel lining based on digital images

采用计算机视觉对隧道衬砌表面的结构病害进行快速无损检测已成为发展趋势,如何通过图像识别结果客观地评定病害严重程度是保障隧道结构服役性能的重要切入点。以地铁盾构隧道衬砌结构表面的裂缝病害二值图像为研究对象,提出客观的新型盾构隧道裂缝诊断指标(Tunnel Defect Index-Crack,简称TDI-C)及其分级标准。首先,通过数字图像处理对裂缝病害进行量化,得到长度、最大宽度、分形维数等3个参数;提出一种动态分块法来计算裂缝病害的长度和最大宽度;采用盒维数计算裂缝病害的分形维数,发现其值越大,所对应裂缝病害的形态越复杂。其次,以200环衬砌管片的隧道区段作为诊断尺度,计算病害量化参数的累计值,建立由21个隧道区段组成的病害样本空间;采用K-means++聚类,合理地确定裂缝病害的分级档数为三级与样本空间中各个样本的病害等级;通过偏最小二乘回归分析,提出隧道裂缝诊断指标TDI-C,并建立病害等级的分级标准。最后,给出地铁区间隧道裂缝病害诊断的应用实例,并指出本文方法较现有方法具有较大优势。

It has become a developing trend to use computer vision to detect structural defects of tunnel lining surface quickly and nondestructively.However,the existing methods for defect diagnosis cannot evaluate the severity of structural defects objectively according to the results of image recognition.In order to overcome the shortcoming,a novel and objective diagnosis index,named tunnel defect index-crack(TDI-C),and grading standard for structural cracks of shield tunnel lining are proposed through binary images.Firstly,three parameters including length,maximum width and fractal dimension are adopted for the quantification of cracks using digital image processing.A dynamic block algorithm is proposed to calculate the length and maximum width of cracks.The fractal dimensions are calculated by box-counting algorithm.The larger the fractal dimension of cracks,the more complex the morphology of cracks.Secondly,taking tunnel section of 200 ring linings as the diagnostic scale,the accumulative value of the defect quantification parameter is calculated.The defect sample space composed of 21 tunnel sections is established.Three levels of structural defect grading and the defect level of each sample in the defect sample space are also determined rationally using the algorithm of K-means++cluster.Through the method of partial least square regression analysis,a novel diagnosis index named TDI-C is proposed,and the grading standard of structural cracks for shield tunnels is established subsequently.Finally,a case study of structural crack diagnosis for metro shield tunnels is introduced to point out that the proposed method has more advantages than the existing methods.