When the dynamic characteristics of a bridge structure are analyzed though Hilbert–Huang transform (HHT), the noise contained in the bridge dynamic monitoring data may seriously affect the performance of the first natural frequency identification. A time-frequency analysis method that integrates wavelet threshold denoising and HHT is proposed to overcome this deficiency. The denoising effect of the experimental analysis on the simulated noisy signals proves the effectiveness of the proposed method. This method is used to perform denoising pre-processing on the dynamic monitoring data of Sutong Bridge, and the denoised results of different methods are compared and analyzed. Then, the best denoising data are selected as the input data of Hilbert spectrum analysis to identify the structural first natural frequency of the bridge. The results indicate that the wavelet-empirical mode decomposition (EMD) method effectively reduces the interference of random noise and eliminates useless intrinsic modal function (IMF) components, and the excellent properties of the signal evaluation index after denoising make the method suitable for processing non-stationary signals with noise. When Hilbert spectrum analysis is applied to the denoised data, the first natural frequency of the bridge structure can be identified clearly and is consistent with the theoretical calculation. The proposed method can effectively determine the natural vibration characteristics of the bridge structure.

The immersed tunnel is composed of elements which are prefabricated elsewhere and floated to the tunnel site to be sunk into the prepared trench. Each element and the closure joint must line up exactly for the watertight gaskets to seal properly. For the construction of extra-long immersed tunnel, particular care should be taken in the perspective of geodetic control. Therefore, the design and implementation of the geodetic basis and hierarchical surface control networks are described. To decrease the influence of lateral refraction and to improve the configuration strength and increase the number of redundant observation compared with traverse, the design of underground surveying network named duo-linear joint chain is presented. The data-processing methodology, including outlier detection for excluding outliers from observation and variance component estimation for realistic precisions of observation, is described. Hong Kong–Zhuhai–Macau immersed tunnel surveying data are analysed and the performance of the geodetic networks and data processing methodology is demonstrated.

Immersed tunnel elements need to be exactly controlled during their immersion process. Position and attitude of the element should be determined quickly and accurately to navigate the element from the holding area to the final location in the tunnel trench. In this paper, a newly-developed positioning and attitude determination system, integrating a 3-antenna Global Navigation Satellite System (GNSS) system, an inclinometer and a range-measurement system, is presented. The system is designed to provide the absolute position of both ends of the element with sufficient accuracy in real time. Special attention in the accuracy analysis is paid to the influence of GNSS multipath error and sound speed profile. Simulations are conducted to illustrate the performance of the system in different scenarios. If both elements are very close, the accuracies of the system are higher than 0.02 m in the directions perpendicular to and along the tunnel axis.

The immersed tunnel which is composed of elements has drawn more attention nowadays because of new advancements and developments. The elements are prefabricated somewhere else and floated to the tunnel site to be sunk into the prepared trench. Each element must line up exactly for the watertight gaskets to seal properly. The HZM immersed tunnel, a key part of the Hong Kong-Zhuhai-Macao Bridge (HZMB) that crosses the Pearl River Estuary and links Hong Kong to the east, and Zhuhai and Macao to the west, is 6.7 km long, one of the longest immersed tunnel ever realized in the world. For the construction of such a mega immersed tunnel, particular care should be taken in the perspective of geodetic control. This paper described the design and implementation of the geodetic basis and hierarchical surface control networks. And to decrease the influence of lateral refraction and to improve the configuration strength and increase the number of redundant observation compared with traverse, the design of underground surveying network named duo-linear joint chain and the results of gyro checks are presented. In the end HZM immersed tunnel surveying data is analyzed and the performance of the control networks is demonstrated.

There is extremely strict precision requirement for the lateral breakthrough error of long immersed tunnel in the offshore island and tunnel project, but the point location layout range of the outer plane control network is limited in the artificial island, and the space inside the tunnel is long and narrow, which is not conducive to high-precision through-measurement control. In order to further reduce the influence of the error of the plane control network on the lateral breakthrough error of the immersed tunnel, a mathematical model of the influence of the lateral breakthrough error caused by the orientation direction of the outer control point and the position of the breakthrough point has been established through the theoretical analysis in this study, and the favorable orientation directions and the favorable penetration point are analyzed. It is suggested through simulation analysis that the direction that is as consistent with that from the entrance (outlet) point to the penetration point as possible is as the advantageous orientation, which could minimize the lateral penetration error and ensure high-precision rendezvous and docking of the immersed tunnel. This study is instructive for similar engineering practices.