Abstract: Experimental research on the maximum shear strain fields of sand specimens with different water contents (12.7%-16.5%) under displacement-controlled loading condition (loading rate is 5 mm/min) is carried out with a digital image correlation method based on the particle swarm optimization algorithm. Also, the influence of the size of subset on the maximum shear strains at different positions of sand specimen is studied. It is found that with the increasing of the water content of sand specimen, deformation becomes even uniform, region of maximum shear strain becomes wider, which reflects an increase in the number of shear bands, and a raise in the maximum shear strain prior to microcrack initiating. With increasing the longitudinal strain, the maximum shear strain increases rapidly in a nonlinear form at region with higher strain, while it generally increases linearly at region with lower strain. After shear bands are generated, especially in a later deformational stage, the size of subset significantly affects the maximum shear strain. The evolution of the maximum shear strain with the size of subset is closely related to the position of subset.

Key words: sand specimen, water content, displacement-controlled loading, shear band, size of subset, maximum shear strain, digital image correlation method