Investigation of centreline strain path during tube penetration using transparent soil and particle image velocimetry

A small-scale physical modelling system was developed and employed to investigate the effects of tube sampling. Amorphous silica and an oil blend of matching refractive index were mixed to form a transparent soil, and black glass beads were embedded within the soil body on the vertical central plane. After consolidation in a Perspex box, round-tipped thick- wall model tube samplers made of glass were pushed into the transparent soil. Movements within the soil body were recorded using digital photography; these images were later analysed by particle image velocimetry. The centreline strain path (CSP) of the sample during tube penetration was calculated and compared to an existing analytical model, and some degree of correlation was observed. However, it was shown that the CSP was not constant throughout the sample, but varied with depth below the base of the borehole. It was also noticed that, after tube penetration, some residual extension strain existed for soil on the centreline. To quantify the effects of sampler geometry parameters on the CSP, further experiments are required to gain an insight into the design of tube samplers, with the aim of producing high-quality soil samples without significantly raising the cost of site investigation.