Improved hilbert spectral representation method and its application to seismic analysis of shield tunnel subjected to spatially correlated ground motions

A novel and efficient method for simulation of spatially correlated earthquake ground motions (SCEGMs), named as improved Hilbert spectral representation method, was presented. By using Hilbert-Huang transform (HHT), the known record can be decomposed into a series of intrinsic mode functions (IMFs) and a residual function. Targeting on each IMF, simulated IMFs for every field point were derived through a spatial correlation model. The frequency dependence of the spatial correlation structure was simplified such that only the correlation at the predominant frequency of each target IMF was considered. SCEGMs can then be obtained by superposition of simulated IMFs and the original residual function. Taking the Suai shield tunnel project in China as reference, the intersegment opening width response of shield tunnel under multiple support excitation (MSE) and identical support excitation (ISE) were investigated and compared. First, numerous accelerograms, including horizontal and vertical components, were generated based on selected real records and artificial acceleration time histories on bedrock to realize MSE. The generalized response displacement method (GRDM) in combination with a large-scale FEM model was then utilized to proceed with the study. Results showed that the MSE can lead to a higher opening width of tunnel in general. The distribution of longitudinal opening width under MSE is also different from that under ISE. The sharp variation of soil layer stiffness along the longitudinal direction of tunnel may lead to extremely large intersegment opening width or severe damage.