Dynamic damage identification of tunnel portal and verification via shaking table test

Abstract

Tunnel portals are seismically weak. Large-scale shaking-table tests of a tunnel portal were conducted. A method based on the Hilbert-Huang transform (HHT) for dynamic damage identification of tunnel portals was studied using the test results. The test preparation process and basic principles of the HHT are briefly described. The intrinsic-mode functions (IMFs) after empirical mode decomposition (EMD) were evaluated using multiple indicators, including the coefficient of determination (R2), root-mean-square error (Rmse), variance contribution rate (Mi), and energy moment (E). The time histories of the IMFs, marginal Hilbert spectrum, and Hilbert instantaneous energy spectrum were analysed. The results show that the damage development process of the lining and slope can be characterised by the marginal Hilbert spectrum and Hilbert Instantaneous energy spectrum. The slope had an obvious acceleration amplification effect with elevation and surface-trend amplification effect. Damage to the tunnel-portal slope is mainly caused by the development of tension cracks at the top of the slope, falling of scattered particles on the slope shoulder, development of cracks on the slope surface, and instability and collapse of the surrounding rock near the tunnel portal. Slope surface damage developed faster and to a greater extent than the interior of the slope. The lining of the portal section was dominated by longitudinal cracks, with some diagonal cracks. Damage to the invert at the tunnel portal occurs earlier than that of the crown, and the degree of injury is greater than that of the crown. The degree of damage and development speed of the tunnel portal were also greater than those of the tunnel body. The proposed method can serve as a guide for identifying the dynamic tunnel-portal damage.