Advanced monitoring and numerical techniques for assessing the stability of tunnels

This research aims to develop an advanced monitoring technique for assessing the stability of tunnels, which may substitute or supplement the conventionally manual procedures. In this paper, 'laser scanning technique' is primarily studied to determine the utilisation of laser scanners for condition monitoring of lined tunnels. A series of model tests have been carried out by using laser scanning technology, in which models were set up simulating tunnel conditions. After scanning and processing in the corresponding software, 3D coordinates of the models were obtained as well as 3D 'point clouds' models. Thus various defect targets like cracks and deformation on the tunnel wall could be identified and measured efficiently in these digital models. Precision and limitations related to laser scanning were also highlighted. In addition, numerical simulation would also be conducted using FLAC ^2D and FLAC ^3D software to link the simulated tunnel behaviours to overall structural stability. This study indicates that laser scanning technique has potential for executing condition monitoring, such as depth and width of cracks, deformation of tunnels, with high accuracy in a static mode of scanning. By these observed information combined with numerical analysis, the stability of the tunnels could be assessed for safety.