Set up, validation, and application of a full-field real-time deformation measurement system for triaxial specimen

In view of the difficulties in volume and deformation measurement of triaxial specimen, this work proposes a full-field deformation measurement system based on a conventional triaxial test apparatus. The cameras with fixed positions in the system for real-time picture capturing, with the aids of photogrammetry, forward intersection, and optical ray tracing, are used to measure the volume and deformation of soil specimen during testing. To validate the feasibility and accuracy of the proposed method, a multi-camera system was established and triaxial test on a steel cylinder and several silt specimens under different confining stresses were conducted. The accuracy of the proposed system for point measurement is 0. 086 mm and for volume measurement is 0. 151%. Triaxial tests on soil specimens revealed that the proposed system is capable of full-field deformation measurement, including the lateral surface and two end surfaces of soil specimen. The full-field measurement results can be further utilized to extract soil volume, 3D reconstruction, axial displacement, axial strain, radial strain, and circumferential strain. By taking advantage of a fixed camera system, the proposed method may significantly simplify photogrammetric analysis, reduce systematic error and improve measurement accuracy with the aids of software package GeoTri3D. The full-field, fine and accurate deformation measurement provides a new tool for advanced characterization of the behavior of soil and other engineering materials. © 2023 Editorial Office of China Civil Engineering Journal. All rights reserved.