ABSTRACT: The mechanical response of rockfill is largely dominated by particle breakage, which is controlled by stress level and the prevailing relative humidity (RH) in the large rockfill voids. The paper presents a model for rockifil behaviour under triaxial stress states, which is based on: (a) existing knowledge on rockfill compressibility, (b) experimental and theoretical developments on sand behaviour and (c) a series of suction-controlled triaxial tests performed in a new large-diameter triaxial cell, in which samples of gravel were tested under two relative humidities: 36% ("dry") and 100% (saturated). Changes in grain size distribution were measured in all the tests performed. The model is formulated within the framework of work hardening plasticity and critical state concepts. Specimen stiffness and limiting conditions depend on the accumulated plastic work and on the prevailing RH. The model reproduces in a satisfactory way the set of triaxial tests performed.

Key words:  elastoplastic model, relative humidity, rockfill, suction, triaxial test (IGC: D6)