Yielding of rockfill in triaxial experiments

Abstract

In recent years, interest in rockfill mechanics has considerable increased, since it has been applied in many geotechnical structures throughout the world. Rockfill is commonly used in road and railway embankments, railway ballast and earth and rockfill dams. Whether its applied in concrete face rockfill dams or embankments for roadways or high-speed train lines, a precise prediction of expected deformations is needed. Since rockfill behaviour started being investigated that significant differences between rockfill and soils behaviour and characteristics were pointed out. A main difference is related to particle breakage, which depends on the strength of particles, particle size distribution, particle geometry and degree of weathering, stress level and relative humidity. Nonetheless, the effect of RH on rockfill behaviour has been neglected both in experiments and in constitutive modelling despite its fundamental effect. The importance of water action, for a wide class of rockfill materials, can be assessed analysing the behaviour of rockfill dams under reservoir impoundment or climatic conditions. This paper presents the results of triaxial tests performed on compacted specimens of a granite rockfill. Different aspects of the rockfill behaviour, important for constitutive modelling, were studied, namely the shape of yielding loci and the dilatancy rules. Dilatancy was described in terms of plastic work input and the shape of the yield locus, in a triaxial plane, was established by different experimental techniques. Yielding loci can be well represented by approximate elliptic shapes, whose major axis follows approximately the K0 line.