Improved image-based deformation measurement for geotechnical applications

Abstract

This paper describes and benchmarks a new implementation of image-based deformation measurement for geotechnical applications. The updated approach combines a range of advances in image analysis algorithms and techniques best suited to geotechnical applications. Performance benchmarking of the new approach has used a series of artificial images subjected to prescribed spatially varying displacement fields. An improvement by at least a factor of 10 in measurement precision is achieved relative to the most commonly used particle image velocimetry (PIV) approach for all deformation modes, including rigid-body displacements, rotations, and strains (compressive and shear). Lastly, an example analysis of a centrifuge model test is used to demonstrate the capabilities of the new approach. The strain field generated by penetration of a flat footing and an entrapped sand plug into an underlying clay layer is computed and compared for both the current and updated algorithms. This analysis demonstrates that the enhanced measurement precision improves the clarity of the interpretation.Key words: image analysis, model tests, particle image velocimetry, digital image correlation.

Synchronised multi-scale image analysis of soil deformations

“…One instance of the software runs in master mode and controls the 'macro' view camera, whilst a second runs in slave mode, assimilating the various settings directly from the master camera. Teng, Y., Stanier, S. A. and Gourvenec, S. (Stanier et al 2015a).…”

“…CCZNCC-tol was specified as 0.75, the maximum number of iterations of the IC-GN optimisation of the deformation parameters for the subset shape function (maxiter) was set to 50 and the maximum difference of the norm of the shape function difference vector (|∆p|max) was set to 1x10 -5 , following the recommendations in Stanier et al (2015a). shows that the μ180 subset used in the analyses of the 'micro' view images suffered from significant decorrelation.…”

“…Pan et al 2010;Blaber et al 2015;Stanier et al 2015a), displacements are generally obtained by: 1) Discretising the region of interest (RoI) within a 'reference' image with a mesh of subsets at a regular spacing interval, then:…”

“…bi-quintic b-spline; Cheng et al 2002). A first-order subset shape function with deformation parameters describing the displacements (u, v) and the displacement gradients (∂u/∂x, ∂v/∂y, ∂u/∂y and ∂v/∂x) (Stanier et al 2015a) is applied.…”

Editorial

“…A major theme in recent research on image analysis has been a re-evaluation of the sources of error in measurements of deformation in opaque geomaterials measured at a transparent boundary (e.g., Stanier et al, 2016a;Stanier et al, 2016b;Take, 2015) and within laser-illuminated planes within transparent soil models (e.g., Iskander et al, 2015). This theme continues in the special issues with Chen et al (2017a) presenting guidelines for the use of DIC in geotechnical engineering research.…”