Non-Target Soil Deformation Mapping by Photogrammetry for Underground Tunnel Model Test

A complex urban environment requires frequent underground tunneling to resolve heavy traffic congestion. With new underground lines being constructed close to existing underground lines the soil deformation around the underground tunnels should be studied and analyzed with proper tunnel model tests. Therefore, we conducted non-target soil deformation mapping using photogrammetry for two different underground tunnel models of sandy soil and clay. Self-calibrated cameras were used to acquire before and after images of the models with the loading test. With accurately estimated exterior orientation parameters (EOPs), the soil deformation was measured via image matchings between two images. Different image matching parameters were tested and the effect of filtering was investigated to produce soil deformation vectors on the images. Experimental results showed that sandy soil and clay required different matching window sizes for the best results. In addition, the deformation vector filtering was helpful to suppress outliers only when an image matching threshold was not applied. With proper matching parameter setup and filtering, the visually informative soil deformation vector map could be generated using photogrammetry.