Calibration and parametric studies using GeoPIV technology to track particle movements in a transparent shear box

GeoPIV is a MATLAB module which uses the principles of particle image velocimetry (PIV) to monitor particles movement during geotechnical tests. To obtain desired output results, several input parameters such as patch size, patch spacing, searchzone pixel, frame rate and leapfrog are required to analyse a batch of sequential images. Inappropriate parameters would produce poor displacement vectors, known as wild vectors. This paper describes the input parameters and also defines the absolute values to be adopted when analysing particle movement during direct shear testing, based on literature and parametric studies. Sequential images were remotely captured during direct shear testing, using a Canon EOS 450D. The tested specimen was well-graded sand, sheared in a custom fabricated transparent shear box. From the current study, the most appropriate input parameters for this test were patch size of 16×16 pixels, patch spacing of 8×8 pixels, search zone of 8×8 pixels, frame rate interval of 50 s and leapfrog of 1. This pre-defining of the input parameters is essential before running any GeoPIV analysis, so as to obtain an accurate and effective displacement vectors.