Following recent rapid developments in tunnel engineering in China,the heavy structural maintenance work of the future is likely to pose a great challenge.Newly developed vibration-based health assessment and monitoring methods offer good prospects for large-scale structural monitoring,hidden surface detection and disease pre-judgment.However,because the dynamic properties of tunnels are sensitive to the coupling and damping effects of the surrounding soil,there is little relevant research on tunnel structures.Using the PiP(pipe in pipe)model,the intrinsic tunnel modes and their response characteristics are investigated in this paper,and the degree to which the identification of these characteristics is influenced by mode superposition and the soil coupling effect are also considered.The response features of these flexible wave modes are found to be barely recognizable in a tunnel-soil coupled system,while the phase velocity of the torsional wave can be determined by combining phase spectrum analysis and the HHT(Hilbert-Huang transformation)method.A new structural health assessment method based on the torsional wave speed is therefore proposed.In this method,the torsional wave speed is used to determine the tunnel structure’s global stiffness based on a newly developed dispersion algorithm.The calculated stiffness is then used to evaluate the tunnel’s structural service status.A field test was also carried out at a newly built tunnel to validate the proposed method;the tunnel structure’s Young’s modulus was obtained and was very close to the designed value.This indicates that this method is an effective way to assess tunnel service conditions,and also provides a theoretical basis for future applications to health assessment of shield tunnels.
Deformation monitoring is vital for tunnel engineering.Traditional monitoring techniques measure only a few data points,which is insufficient to understand the deformation of the entire tunnel.Terrestrial Laser Scanning(TLS)is a newly developed technique that can collect thousands of data points in a few minutes,with promising applications to tunnel deformation monitoring.The raw point cloud collected from TLS cannot display tunnel deformation;therefore,a new 3D modeling algorithm was developed for this purpose.The 3D modeling algorithm includes modules for preprocessing the point cloud,extracting the tunnel axis,performing coordinate transformations,performing noise reduction and generating the 3D model.Measurement results from TLS were compared to the results of total station and numerical simulation,confirming the reliability of TLS for tunnel deformation monitoring.Finally,a case study of the Shanghai West Changjiang Road tunnel is introduced,where TLS was applied to measure shield tunnel deformation over multiple sections.Settlement,segment dislocation and cross section convergence were measured and visualized using the proposed 3D modeling algorithm.
In this work,deformations and internal forces of an existing tunnel subjected to a closely overlapped shield tunneling are monitored and analyzed using a series of physical model experiments and numerical simulations.Effects of different excavation sequences and speeds are explicitly considered in the analysis.The results of the physical model experiments show that the bottom-up tunneling procedure is better than the top-down tunneling procedure.The incurred deformations and internal forces of the existing tunnel increase with the excavation speed and the range of influence areas also increase accordingly.For construction process control,real-time monitoring of the power tunnel is used.The monitoring processes feature full automation,adjustable frequency,real-time monitor and dynamic feedback,which are used to guide the construction to achieve micro-disturbance control.In accordance with the situation of crossing construction,a numerical study on the performance of power tunnel is carried out.Construction control measures are given for the undercrossing construction,which helps to accomplish the desired result and meet protection requirements of the existing tunnel structure.Finally,monitoring data and numerical results are compared,and the displacement and joint fracture change models in the power tunnel subject to the overlapped shield tunnel construction are analyzed.
