三轴试样全表面精细重建技术研究

    Fine reconstruction of full-surface of soil specimens during triaxial testing

    • 摘要: 非接触式图像法越来越广泛地应用于岩土体在室内试验过程中的变形测量。然而,由于光线折射和点云采集难题,针对三轴试样表面的精细测量仍极具挑战性。研究提出了一个融合6台相机、超薄透明乳胶膜、3D-DIC技术和多光学介质摄影测量法,以及配套软件GeoTri3D的测量系统来实现加载过程中三轴试样全表面的精细重建。通过不锈钢柱和粉土试样的三轴测试,验证了该系统的适用性和测量精度。多光学介质摄影测量法实现了严谨的光线折射校正并将3D-DIC的应用从单一光学介质扩展到了多介质条件;同时,3D-DIC技术显著提高了多光学介质摄影测量的分辨率与点云生成效率。粉土三轴试验结果表明该系统能够实现试样全表面的精细重建,对于试样表面特定兴趣区域(ROI),测量分辨率可提升至6034.7点/cm2,为多光学介质条件下的土样变形精细测量提供了解决方案。

       

      Abstract: Noncontact image-based methods are becoming increasingly popular for characterization of geomaterials deformation during laboratory loading. However, surface reconstruction of a specimen inside a triaxial chamber is still challenging due to difficulties in handling optical ray refraction point cloud acquisition. A new system, which includes six cameras, an ultra-thin transparent membrane, the 3D-DIC technique, and multi-media photogrammetric methods and the associated software package GeoTri3D, is proposed to reconstruct soil surface during triaxial loading. Tests on a stainless-steel cylinder and silt specimens are performed to evaluate the proposed system. The multi-media photogrammetric method is able to rigorously correct the effect of optical ray refraction and extends the application of 3D-DIC from single medium to multi-media conditions. Meanwhile, the introduction of 3D-DIC significantly increases the resolution of the multi-media photogrammetric measurement and reduces the time and effort required for generation of dense point clouds. With the proposed system, the specimen surface can be photo-realistically reconstructed, which offers an accurate and data-rich solution for advanced material characterization under multi-optical-media conditions. Furthermore, for a specific region of interest (ROI) on the specimen surface, the measurement resolution can be significantly increased up to an ultra-high level (i.e.6034.7 dots/cm2), which is particularly favorable for localized deformation characterization.

       

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