A Fast Metro Tunnel Profile Measuring Method Based on Close-Range Photogrammetry

With the rapid development of subway tunnel all over the world, inspecting tunnel structure has become a difficult task. Traditional manual inspection methods have begun to be unable to meet the development needs. Therefore, an efficient and precise measuring method is urgently needed for this purpose. In the present study, based on the close-range photogrammetry, a novel method is proposed for measuring the subway tunnel profile. Based on the proposed method, a new measurement device, namely Moving Tunnel Profile Measurement (MTPM-1), was developed. In situ tests were carried out in the tunnel of Shanghai Metro Line 4 in order to analyze the effect of several factors on measurement precision. For the tunnel with an inner diameter of 5.5 m, the maximum measurement error was below 5 mm. The method was proved to be feasible and precise. During the field tests, a 100-m 3D shape of tunnel was captured by MTPM-1 within 3 min. The standard operation procedure was proposed using MTPM-1 for any other tunnel. The profile information would then provide crucial data basis for tunnel performance assessment.