The triaxial test based on photogrammetry can realize the real-time measurement of the local deformation of the specimen, but the refraction of light leads to the error in the measurement of specimen deformation. The introduction of the refraction correction factor (κ) can not only solve this problem, but also improve the test efficiency. In order to investigate the trend of the refraction correction coefficient in the axial and radial deformation measurements of different specimens, and to analyze the difference between the stress-strain curves measured by applying the refraction correction coefficient and those of the conventional triaxial tests, the photogrammetric-based consolidation and drainage triaxial tests were carried out on red clay and sandy clay, respectively. The results show that: (1) In the axial deformation measurement, the refraction correction coefficients of the different local regions of the red clay and the sandy clay converged to 1, and the refraction amplification effect on the axial deformation measurement of the specimen is negligible; (2) In the radial deformation measurement, the refraction correction coefficients of the red clay and sandy soil are 0.812 and 0.757, respectively. The refraction amplification effect has a greater impact on the radial deformation measurement of the specimen, and the refraction correction coefficients of the different specimens correspond to different refraction correction coefficients; (3) The change trends of the stress-strain curves measured by conventional triaxial and the application of refraction correction coefficient. The stress-strain curves measured by conventional triaxial and by applying the refraction correction coefficient have the same trend, and the bias stress measured by applying the refraction correction coefficient photogrammetry is relatively small in the middle and late stages of the test.
[1] 张崇磊, 朱秦, 李丞,等.中等压缩性粉质黏土不排水剪切强度试验研究[J].地下空间与工程学报, 2019, 15(6): 1620-1629.(Zhang Chonglei, Zhu Qin, Li Cheng, et al.Experimental study on undrained shear strength of medium-compressibility silty clay[J].Chinese Journal of Underground Space and Engineering, 2019, 15(6): 1620-1629.(in Chinese))
[2] 刘勇健,杨鑫,李彰明,等.剪切应变速率对淤泥土力学性状影响试验研究[J].地下空间与工程学报,2019,15(1):68-75.(Liu Yongjian,Yang Xin,Li Zhangming,et al.Experimental study on effects of shear strain rate on mechanical behavior of muck soil[J].Chinese Journal of Underground Space and Engineering,2019,15(1):68-75.(in Chinese))
[3] 李泉,吴楠,肖军华.考虑应力路径的软黏土小应变特性试验研究[J].地下空间与工程学报,2021,17(5):1486-1494.(Li Quan,Wu Nan,Xiao Junhua.Experimental study on the small-strain characteristics of soft clay considering stress paths[J].Chinese Journal of Underground Space and Engineering,2021,17(5):1486-1494.(in Chinese))
[4] 高彬,陈筠,杨恒,等.红黏土在不同应力路径下的力学特性试验研究[J].地下空间与工程学报,2018,14(5):1202-1212.(Gao Bin,Chen Jun,Yang Heng,et al.Experimental study on mechanical properties of red clay under different stress paths[J].Chinese Journal of Underground Space and Engineering,2018,14(5):1202-1212.(in Chinese))
[5] Xia Y, Mu C M, Li W J, et al.Study of dynamic evolution of the shear band in triaxial soil samples using photogrammetry technology[J].Sustainability, 2022, 14(21): 14660.
[6] 吴浩杰.基于图像测量的三轴土样变形特性研究[D].桂林: 桂林理工大学, 2021.(Wu Haojie.Study on deformation characteristics of triaxial soil samples based on image measurement[D].Guilin: Guilin University of Technology, 2021.(in Chinese))
[7] Gachet P, Geiser F, Laloui L, et al.Automated digital image processing for volume change measurement in triaxial cells[J].Geotechnical Testing Journal, 2006, 30(2): 98-103.
[8] Rechenmacher A L, Medina-Cetina Z.Calibration of soil constitutive models with spatially varying parameters[J].Journal of Geotechnical and Geoenvironmental Engineering, 2007, 133(12): 1567-1576.
[9] Bhandari A, Powrie W, Harkness R.A digital image-based deformation measurement system for triaxial tests[J].Geotechnical Testing Journal,2012, 35(2): 209-226.
[10] Salazar S, Coffman R.Consideration of internal board camera optics for triaxial testing applications[J].Geotechnical Testing Journal, 2015, 38(1): 40-49.
[11] Shao L T, Liu X, Guo X X, et al.Digital image technique for deformation measurement of unsaturated soil specimen in triaxial test[M].Unsaturated Soils: Research & Applications.CRC Press, 2020.
[12] 王鹏鹏, 郭晓霞, 桑勇,等.基于数字图像相关技术的砂土全场变形测量及其DEM数值模拟[J].工程力学, 2020, 37(1): 239-247.(Wang Pengpeng, Guo Xiaoxia, Sang Yong 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))
[13] 李林, 沈珂任, 王林,等.三轴试样全息变形实时测量系统的搭建、验证与应用[J].土木工程学报, 2023, 56(8): 108-117.(Li Lin, Shen Keren, Wang Lin et al.Set up, validation, and application of a full-field real-time deformation measurement system for triaxial specimen[J].Journal of Civil Engineering, 2023, 56(8): 108-117.(in Chinese))
[14] Fayek S, Xia X, Li L, et al.Photogrammetry-based method to determine the absolute volume of soil specimen during triaxial testing[J].Transportation Research Record, 2020, 2674(8): 206-218.
[15] Li L, Zhang X.Factors influencing the accuracy of the photogrammetry-based deformation measurement method[J].Acta geotechnica, 2019, 14: 559-574.
[16] 李尚明, 洪成雨, 姬凤玲, 等.深基坑的机器视觉监测与变形预测研究[J].地下空间与工程学报, 2023, 19(3): 992-1000.(Li Shangming, Hong Chengyu, Ji Fengling, et al.Study on machine vision monitoring and deformation prediction of deep foundation pit[J].Chinese Journal of Underground Space and Engineering, 2023, 19(3): 992-1000.(in Chinese))
[17] 叶锴, 夏燚, 牟春梅.三维折射修正模型在试样变形测量中的应用[J].人民长江, 2023, 54(7): 172-179.(Ye Kai, Xia Yi, Mou Chunmei.Application of three-dimensional refraction correction model in soil sample deformation measurement[J].People's Yangtze River, 2023, 54(7): 172-179.(in Chinese))
[18] 闫润, 黄立波, 郭辉, 等.实时光线追踪相关研究综述[J].计算机科学与探索, 2023, 17(2): 263-278.(Yan Run, Huang Libo, Guo Hui et al.Review of real-time ray tracing technique research[J].Computer Science and Exploration, 2023, 17(2): 263-278.(in Chinese))
[19] Xia X, Zhang X, Mu C.A multi-camera based photogrammetric method for three-dimensional full-field displacement measurements of geosynthetics during tensile test[J].Geotextiles and Geomembranes, 2021, 49(5): 1192-1210.
[20] Li L, Zhang X, Chen G, et al.Measuring unsaturated soil deformations during triaxial testing using a photogrammetry-based method[J].Canadian Geotechnical Journal, 2015, 53(3): 472-489.
