基于摄影测量法的三轴试验可以实现试样局部变形的实时测量,但由于光线折射作用导致试样变形测量产生误差。通过引入折射修正系数(κ)不仅可以解决此问题,而且可以提高试验效率。为了探究不同试样轴向、径向变形测量中的折射修正系数变化趋势,分析应用折射修正系数测得的应力—应变曲线与常规三轴试验的差异,分别对红黏土和砂土开展基于摄影测量的固结排水三轴试验,结果表明:(1)在轴向变形测量中,红黏土和砂土不同局部区域的折射修正系数均趋近1,折射放大效应对试样轴向变形测量的影响可忽略不计;(2)在径向变形测量中,红黏土和砂土的折射修正系数分别为0.812和0.757,折射放大效应对试样径向变形测量的影响较大,且不同试样对应不同的折射修正系数;(3)常规三轴与应用折射修正系数所测得的应力—应变曲线变化趋势一致,在试验中后期,应用折射修正系数摄影测量测得的偏应力相对较小。
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.
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