Development of a Robust Stereo-PIV System for 3-D Soil Deformation Measurement

This paper presents a robust stereo-particle image velocimetry (Stereo-PIV) system developed for three-dimensional (3-D) soil deformation measurement in geotechnical engineering. Also known as digital image correlation, PIV is a popular image processing technique to measure two-dimensional (2-D) fluid velocity in fluid dynamics. The Stereo-PIV technique extends 2-D deformation measurement to 3-D based on a binocular vision model, where two cameras with a well posed geometrical setting, are utilized to image the same object. Although commercial Stereo-PIV systems are available in the market, the applications of this technique are still limited by their high cost and special hardware requirements. This study presents a robust Stereo-PIV system, which utilizes two standard complementary metal–oxide–semiconductor (CMOS) cameras and two open software packages to apply this technique to geotechnical engineering testing. In order to apply this technique, three steps have to be performed: the first step is the calibration for the system to get the parameters of the two cameras with respect to the region of interest (ROI); the second step is to obtain a series of paired images of the ROI during deformation and calculate the corresponding 2-D displacement fields from these images; and the last step is to construct a 3-D displacement field based on the camera parameters calculated in the first step and the corresponding 2-D displacement vector pairs from the second step. The developed system is applied in a model test to measure 3-D sand deformation around a laterally loaded pile. The results demonstrate that the system can obtain a reasonable result and can be readily adjusted for more advanced 3-D deformation measurement in geotechnical engineering research.