Studies on automatic extraction of precise 3D laser measurement data in specific section of subway tunnel

In the construction period and operation period of an urban subway, due to the comprehensive impact of geology, groundwater, the construction of adjacent foundation pits and the load of its own structure, the tunnel structure of the subway may go through deformation and other changes that endanger the safety of the tunnel. With the growing scales of subways and tunnels projects, structure monitoring becomes increasingly important and a fast and accurate extraction method is critical for the monitoring of tunnel structures. In this paper, a method of extracting tunnel section based on gray map is proposed to fit the tunnel section, which is applied in a subway tunnel interval in Suzhou city. Data such as horizontal convergence value and ellipticity of a particular section in the test interval are extracted, and the results are compared with those measured by the total station measurement method at the same time. The results show that the proposed method can extract a specific section accurately and takes a short computing time. Compared to the traditional total station measurement method, the 3D laser measuring method not only improves the efficiency and data comparability of the tunnel deformation in the long-term operation monitoring, but also makes it easier for structured data to be used in the evaluation of the tunnel operation status and the development trend of the long-term deformation of a tunnel.