Effect of Grain Size and Shape on Undrained Behaviour of Sands

Abstract

The stress–strain and stress path characteristics of sands are influenced by their grain size, shape, and packing. Morphological characteristics and size of particles play important role on the undrained shear strength of sands. Often, effects of these parameters are complex and cannot be easily distinguished. This study advances the knowledge of the role of particle size and shape on the undrained shear strength of sands. To eliminate the consequence of morphological characteristics, two sands with different particle sizes but similar angularity, and another sand with different roundness were selected for the study. These morphological characteristics for all three sands were determined from the analysis of scanning electron microscope images. F131 sand with higher median grain size and lower shape factors (rr and rs) had highest undrained peak shear strength and phase transformation value. Undrained strength (qpt) and effective principal stress (P′pt) in phase transformation point had direct relationship with grain median grain size (D50) and inversely effect of shape factor (rr and rs). F131 and F161 sands represented highest peak and ultimate steady-state strengths, respectively. Flow potential appeared to be directly proportional with (rr and rs) and inversely with D50. The peak index decreased with increasing shape factors (rr and rs).