Consideration of One Camera Photogrammetry-Based Method to Reevaluate Some Aspects of Conventional Triaxial Testing

Triaxial tests have been extensively used in geotechnical engineering to determine soil characteristics and investigate soil behavior. However, little research has been carried to evaluate important aspects of common triaxial testing that can cause misleading interpretation of soil properties. The key reason for this is the absence of a proper and affordable method to monitor the actual soil behavior during various steps of triaxial testing. Recently, a photogrammetry-based method was proposed and proved highly accurate measurements of local, total, and absolute volumes, specimen deformations, and strain localization. This paper suggests a practical re-evaluation of some aspects and practices in the conventional triaxial testing by applying the advancement of the photogrammetry-based technique. The analysis of a series of drained triaxial compression tests using the photogrammetry-based method proved the ability to determine the tilting, the misalignment, and the likelihood of leakage during saturation of soil specimen, and the preparatory, consolidation, and shearing stages of triaxial testing. The experimental results presented relevant insights about the major errors during laboratory procedures and testing including the deviation of the effective stress path, maximum shear stress, axial strain, stress–strain relationship, and soil strength. The measurement of the eccentricity and tilting angle of soil specimen provided proof of potential errors and are recommended to be considered to evaluate the reliability of soil characteristics measurement during triaxial testing. In addition to that, the procedure presented in this paper reinforces the importance of the adoption of the photogrammetry-based method to accurately determine the soil properties during triaxial testing.