This is similar to the approach used in (which uses triangular
shape functions to interpolate displacements):
Desrues, J., & Viggiani, G. (2004). Strain localization in sand: an overview of the experimental results obtained in Grenoble using stereophotogrammetry. International Journal for Numerical and Analytical Methods in Geomechanics, 28(4), 279-321.
Desrues, J., & Viggiani, G. (2004). Strain localization in sand: an overview of the experimental results obtained in Grenoble using stereophotogrammetry. International Journal for Numerical and Analytical Methods in Geomechanics, 28(4), 279-321.