Subway Tunnel Structural Deformation Monitoring Method Based on Machine Vision Measurement

[Objective] Tunnel deformation is related to the health of the tunnel structure, and accurate monitoring of tunnel deformation is very important for tunnel safety. Although traditional manual measurement methods are relatively accurate, the time-consuming and labor-intensive defects making it difficult to meet the efficient operation and maintenance requirements of large-scale tunnels; while automatic monitoring methods are mainly based on imported fully automatic total stations, with limited measurement range and high equipment costs. It is urgent to develop new efficient and low-cost measurement technologies. [Method] Based on machine vision measurement, large-scale multi-point deformation monitoring of subway tunnel structures can be achieved in a single-camera mode, which can take into account both monitoring frequency and accuracy, featuring the advantages of being simple and fast. First, after selecting the camera parameters, the magnification at each monitoring point is calibrated; at the same time, the grayscale centroid method is used to quickly calculate the center coordinates of the light spot and its change during the monitoring process; finally, the magnification is used to realize the conversion of pixel coordinate changes to actual physical coordinates, thereby obtaining the actual displacement deformation of each monitoring point. [Result & Conclusion] Based on machine vision methods, a 28-day displacement monitoring experiment is conducted on a 120m subway tunnel section. The experimental results show that both the horizontal and vertical displacements of the target tunnel section are within 1.5mm, and both exhibit an overall trend of periodic fluctuations. This verifies that machine vision monitoring of subway tunnels can achieve long-term continuous and accurate monitoring of millimeter-level subway tunnel deformation.