Small-strain stiffness characteristics of granular materials under monotonic and cyclic loading: effects of particle breakage

Particle breakage significantly affects soil dilatancy and critical state at large strains (greater than 1%). However, its quantitative impacts on small-strain stiffness characteristics have not been well understood. In this study, two types of construction and demolition waste (concrete and brick particles) were tested, as they are commonly recycled in geotechnical engineering. Monotonic and cyclic oedometer tests with bender elements were conducted under dry and soaked conditions to measure the particle breakage and the small-strain shear modulus (G0). The measured G0 value was normalised by a void ratio function F(e) to eliminate void ratio effects. The particle breakage induces a reduction of G0/F(e) because the decrease in mean particle size and the increase in surface roughness caused by particle breakage diminish the inter-particle contact quality. Furthermore, under cyclic loads, two competing mechanisms emerge with increasing number of cycles: particle breakage tends to decrease G0/F(e); the enhancement of inter-particle contacts and the increase in K0 tend to increase G0/F(e). Whether the G0/F(e) increases or decreases with the number of cycles depends on which of these two mechanisms is dominant. Based on experimental observations, a new simple model for G0 considering particle breakage was proposed under one-dimensional compression and monotonic loading conditions.