High Contrast Particle Staining method for transparent soil and its experimental application

In the joint application of transparent soil testing technology and digital image correlation technology, the quality stability of speckle pattern directly determines image acquisition and measurement accuracy. The High Contrast Particle Staining (HCPS) method is proposed for the stable high-quality transparent soil speckle patterns, which is evaluated by MIG and zero-displacement test to determine the optimal configuration ratio of speckles. The application effects are verified through a transparent model test of rectangular pipe-jacking, the internal evolution process of surface deformation law and back-soil effect are elaborated by using displacement nephograms vector diagrams and curves combined with field monitoring data. The results show that: (1) The optimal staining agents for transparent soil is black water-based chromatin solution and white water-based matte paint, and the optimal configuration ratio B∶W is 8:10. At the moment, the MIG is the highest, the strain nephogram is flat and has the least identification error of speckle over-range. (2) The results of transparent soil model test and field monitoring data jointly revealed the occurrence of back-soil effect of rectangular pipe-jacking. It includes subside area, compensation area and uplift area gradually appearing along the jacking direction, and the occurrence of back-soil effect is continuous in long-distance projects. (3) The uplift of subside area and compensation area is caused by jacking pressure, and the uplift area is the influence of jacking pressure and pipe-soil friction. The regional uplift deformation caused by pipe-soil friction is twice than that caused by jacking pressure. (4) HCPS method avoids problems of overexposure, distortion, interference, and lack of information, and has achieved a good experimental application effect.