Abstract: Triaxial test is widely utilized for characterizing soil mechanical behavior, during which soil volume and deformation is required to be measured. This paper introduces a real-time and precise measurement method for soil volume and deformation during triaxial testing, achieved through a GeoPIV-RG based approach using multi-media photogrammetry. This measurement process encompasses system setup, image capturing, multi-camera photogrammetric analysis, GeoPIV-RG-based 2D point cloud generation, 3D point cloud generation, point cloud stitching, end cut, mesh generation, and interpolation, followed by displacement and strain field calculation. To validate the accuracy and feasibility of this method, triaxial tests were conducted on steel cylinder and silt specimens. Test on steel cylinder confirmed that the proposed method accomplished soil volume measurement with an error of only 0.36%, while triaxial test on silt specimen demonstrated the method's capability in real-time and high-resolution full-field measurement of soil deformation. GeoPIV-RG enables the efficient extraction of point clouds on specimen surfaces and overcomes the limitations of the multi-media photogrammetric method. Moreover, the multi-media photogrammetric method broadens the application of GeoPIV-RG from two-dimensional and single-medium conditions to three-dimensional and multi-media settings. Overall, the proposed method presents an efficient and reliable solution for measuring soil deformation during triaxial testing.

Key words: GeoPIV-RG, photogrammetry, triaxial test, sample volume, full-field deformation