Volume change of triaxial soil samples based on photogrammetry technology
（1. College of Civil and Architectural Engineering, Guilin University of Technology, Guilin, Guangxi 541004, China; 2. Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering, Guilin University of Technology, Guilin, Guangxi 541004, China）
Abstract：Based on the new photogrammetry technology, the calculation results of the soil sample marker coordinates were corrected by the least square method and the refractive correction coefficient, and the three-dimensional coordinates of the soil sample deformation were calculated. The boundary function method was used in MATLAB software to calculate the volume change data of each part of the soil sample. According to this principle， the unconsolidated and undrained（UU） tests of saturated red clay samples from Guilin, Guangxi under different confining pressures were carried out. The test results show that the "true deformation measurement" of the soil sample in different deformation stages can be completed by photogrammetry, and the deviator stress of the soil sample is 5.7% smaller than that of the conventional measurement method. The overall and local volume change data of the soil sample under non-uniform deformation are obtained by the new photogrammetry technology, which can take into account both measurement and reduction of 3D model of soil sample, and the non-contact volume change data measurement is realized.
LI L, LI P, CAI Y, et al. Visualization of non-uniform soil deformation during triaxial testing[J]. Acta Geote-chnica, 2021, 16(11): 3439-3454.
［2］
刘港. 基于全表面测量的三轴土样剪切破坏过程研究[D]. 大连：大连理工大学, 2017.
［3］
DESRUES J, CHAMBON R, MOKNI M, et al. Void ratio evolution inside shear bands in triaxial sand specimens studied by computed tomography[J]. Géotechnique, 1996, 46(3): 529-546.
［4］
LIN H, PENUMADU D. Strain localization in combined axial-torsional testing on kaolin clay[J]. Journal of Engineering Mechanics, 2006, 132(5): 555-564.
［5］
SALAZAR S, COFFMAN R. Consideration of internal board camera optics for triaxial testing applications[J]. Geotechnical Testing Journal, 2015, 38(1): 40-49.
［6］
SALAZAR S, BARNES A, COFFMAN R. Development of an internal camera-based volume determination system for triaxial testing[J]. Geotechnical Testing Journal, 2015, 38(4): 549-555.
SHAO L T, LIU G, GUO X X. Effects of strain localization of triaxial samples in post-failure state[J]. Chinese Journal of Geotechnical Engineering, 2016, 38(3): 385-394. (in Chinese)
WANG P P,GUO X X, SANG Y, et al. Full-field deformation measurement of sand using the digital image correlation technique and numerical simulation using the discrete element method[J]. Engineering Mechanics, 2020, 37(1): 239-247. (in Chinese)
［9］
ZHANG X, LI L, CHEN G, et al. A photogrammetry-based method to measure total and local volume changes of unsaturated soils during triaxial testing[J]. Acta Geotechnica, 2015, 10(1): 55-82.
［10］
LI L, ZHANG X, CHEN G, et al. Measuring unsatura-ted soil deformations during triaxial testing using a photogrammetry-based method[J]. Canadian Geotechnical Journal, 2016, 53(3): 472-489.
