AbstractParticle breakage plays a relevant role on the stress-strain behavior of rockfills. As is widely recognized, the amount of particle breakage of coarse-grained soils depends on a combination of several factors, namely grain size, mineralogy, the shape of the particles, stress level, and degree of saturation and its variation. The results of monotonic triaxial tests carried out on a large apparatus on specimens of two types of rockfills and three different gradings highlighted the role of the coefficient of uniformity, grain tensile strength, and loading path on particle breakage and overall soil behavior. Starting from experimental evidence, a simplified conceptual model to predict the level of breakage during a generic stress path was developed. Experimental data supported the hypothesis of the influence of particle breakage on the position of the critical state lines (CSLs) in the compression plane. This implies that CSL parameters are state dependent, changing with current grading modifications, and are not intrinsic. A simplified procedure for predicting the position of the CSLs as a function of current particle breakage was, therefore, developed and calibrated against laboratory test results.