三维折射修正模型在土样变形测量中的应用

Application of three-dimensional refraction correction model in soil sample deformation measurement

三轴试验的摄影测量中,压力室和不同介质产生的折射放大效应对测量结果影响很大。为探寻工程特性完全不同的土对折射效应的敏感程度,基于光线追踪技术建立了三维折射修正模型,选取具有代表性的桂林红黏土与一般砂土作为试验材料进行研究。试验中以摄影测量法直接得到土样变形值作为折射修正前值,以消除折射影响的土样变形值作为折射修正后值,选择轴向变形值和径向变形值作为考虑折射效应的影响指标。试验结果表明:(1)折射效应的影响对两种土样的轴向变形可以忽略不计,但对径向变形起到了放大作用,红黏土在径向上放大1.25倍,砂土在径向上放大1.32倍;(2)摄影测量法应用于三轴试验变形测量时,不能通过一个固定的修正系数实现对所有不同土样的折射修正,而是要针对不同土样的工程特性给出不同的折射修正系数。

With regard to the photogrammetry in triaxial tests,the refraction amplification effects from pressure chamber and different media exert great influences on the accuracy of photogrammetry results.In order to investigate the sensitivity of soils with completely different engineering properties to the refraction effect,this study selected the representative Guilin red clay and a general sandy soil as test materials,then a three-dimensional refraction correction model was established based on ray tracing technology.The deformation value of the soil sample directly obtained by photogrammetry was taken as a pre-corrected value of refraction,while the eliminated-refraction deformation value of the soil sample was taken as a post-corrected value of refraction.The axial deformation value and radial deformation value were incorporated as the influencing indexes to study the effect of refraction.By examining the deformation values of the two soil samples,the following results were obtained:①The influence of refraction effect on the axial deformation of the two soil samples was slight,yet the radial deformation played an amplifying role,making the red clay deformation amplified 1.25 times in the radial direction,and the sandy soil deformation amplified 1.32 times;②When the photogrammetry method was applied to the triaxial test deformation measurement,the refraction for different soil samples cannot be corrected by a fixed correction factor.In this case,the engineering characteristics of different soil samples should be considered,and different refractive correction coefficients should be given.