Cross-section Positioning Based on a Dynamic MLS Tunnel Monitoring System

The number of tunnels is increasing sharply, especially in China, due to the development of urban rail transit networks. It is thus crucial to study rapid structural deformation detection methods for tunnels in operation. A dynamic tunnel monitoring system can directly obtain cross sections. However, using only odometers to locate the cross sections along the track of a tunnel results in insufficient accuracy. Furthermore, the measured cross sections are all in local coordinate systems, providing no indication of curved tunnels and restricting 3D display capabilities. This paper focuses on a relative positioning method based on mobile laser scanning to improve the accuracy, together with a unified positioning method to relate the measured cross sections in a single system. The accuracy and applicability of the proposed methods are verified by experiments which demonstrate that the solutions can fully meet accuracy requirements and 3D display purposes.