考虑折射影响的摄影测量法土工三轴模型精度分析

Accuracy analysis of photogrammetric triaxial model considering the influence of refraction

将摄影测量法用于土工三轴试验,可获得土样形变场,但光线穿越压力室及水所产生的折射影响试验的精度。如何消除折射的影响,提高三轴土样变形测量的精度是该研究的核心。以附有标记点的硬质圆柱为研究模型,通过摄影测量的三轴模拟试验,建立折射修正模型对折射误差进行校正,获取三轴模型分别在空气中、注水压力室以及折射修正后三种情况下的轴向值与径向值,并以空气中三轴模型的游标卡尺测量值为“基准值”,分别将注水压力室和折射修正后所获取的模型尺寸测量值与“基准值”进行对比,分析折射对三轴模型的成像影响。结果表明:摄影测量法在空气中具有较高的测量精度,通过折射修正模型可以有效减少折射误差,经折射修正后径向平均误差为0.63%,轴向平均误差为0.23%,这与折射修正前的径向平均误差和轴向平均误差相比分别减少26.29%和3.09%;折射对三轴模型轴向与径向的影响不一致,轴向受折射影响不如径向显著,且三轴模型各方向受到的折射影响各不相同。

The photogrammetric method was used in geotechnical triaxial test to obtain the dimensional deformation field of soil samples, but the refraction caused by the light passing through the pressure chamber and water would affect the accuracy of the test. How to eliminating the influence of refraction and improving the accuracy of triaxial soil deformation measurement is the key of the research. The authors used the hard cylinder with marked points as the research model, then established a refraction correction model to correct the refraction error through the three-axis simulation experiment of photogrammetry to obtain the axial and radial values of the triaxial model in air, water injection pressure chamber and after refraction correction. Besides,they defined the measured value of the vernier caliper of the triaxial model in the air as the “reference value”,compared the measured value of the model size obtained after the water injection pressure chamber and refraction correction with the “reference value”, and analyzed the influence of refraction on the imaging of the triaxial model. As shown in the results: Photogrammetry has high measurement accuracy in air. The refraction error can be effectively reduced through the refraction correction model. After refraction correction, the radial average error is 0.63% and the axial average error is 0.23%, which was reduced by 26.29% and 3.09%respectively compared with the radial average error and axial average error before refraction correction. The influence of refraction on the axial and radial directions of the triaxial model is inconsistent, the influence of refraction on the axial direction is not as significant as that on the radial direction, and the influence of refraction on each direction of the triaxial model is different.