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Cavity Location Method for Operational Metro Tunnels Based on Perturbation Theory
Ling Wan,Xiongyao Xie,Lujun Wang,Pan Li,Hua Yin 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.6
Disease in the liner back cavities of operational metro tunnels is alternately affected by groundwater environment, train cyclic load, and ambient environment conditions. Cavity disease is characterized by high levels of hiddenness and uncertainty; it also easily induces other tunnel diseases which can reduce the structure’s bearing capacity and degrade structural safety and stability throughout the tunnel. This paper proposes a novel cavity-locating method for operational shield tunnels, with special focus on single- and multiple-cavity diseases. Based on perturbation theory, dynamic behaviors (modal frequencies and shapes) of different cavity cases were obtained from an analytical model of the original tunnel structure. A modal strain energy cavity indicator (MSECI) was established to reveal the locations of both single cavity and multiple cavities. A typical shield tunnel was modeled as an Euler-Bernoulli beam on a Winkler foundation and evaluated to validate the proposed method. The perturbation theory appears to effectively characterize the dynamic characteristics of liner back cavities in metro tunnels. MSECI can be used to locate cavities accurately. This work may provide a valuable theoretical basis for the detection and analysis of tunnel cavity disease and other tunnel health-monitoring applications.
Ling Wan,Xiongyao Xie,Lujun Wang,Pan Li,Yong Lu 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.1
The structural health of operational metro tunnels is closely related to public safety. Prior research has focused on the locations of structural damage, but few researchers have examined both the location of damage and identifying the degree of damage, especially in metro shield tunnels. This paper proposes a new method for identifying structural damage that entails locating and detecting the degradation of tunnel performance, with a special focus on characterizing the degree of damage. First, the dynamic behaviors (modal frequencies and shapes) of different damage levels are obtained from an analytical model of the original tunnel structure. Second, a modal strain energy damage indicator (MSEDI) is introduced to locate the damage, regardless of size. Once the location of the damage is identified using MSEDI, a fuzzy logic-based damage identification (FLBDI) method is used to determine the actual extent of the damage. Finally, a simplified model of the tunnel is created using the Euler-Bernoulli beam theory and Winkler’s foundation, to further test the procedure under an incomplete modal information condition and with differing noise levels. The results reveal that the fuzzy logic-based system can identify the degree of damage and structural degradation with very high accuracy, in which the location of damage and the prediction of performance degradation is satisfactorily confirmed.