Constitutive Modelling of Geomaterials

Research focus

The Peer review has evaluated this group as Excellent

Geomaterials are materials of geologic or anthropic origin made of elementary particles or grains, stuck together by chemical bonds. The overall behaviour of the material is governed by the geometry of the particle array, by the intergranular friction and by the bond strength and stiffness. The bonding level can be strong (e.g. granite), weak (e.g. tuff) or nil (e.g. sand). Bonding level can decrease in time (weathering) or increase for natural (diagenesis) or anthropic reasons (e.g. grouting). It is affected by many factors either mechanical (e.g. bond crushing under load) or not (e.g. temperature effects). The study of the mechanical behaviour of geomaterials is of fundamental importance to any engineering problem involving soils or rocks (e.g. foundations, tunnelling, retaining structures, slopes, mining etc.) In order to determine pressures on structures and to predict their movement, we need in fact to describe the behaviour of the geomaterial interacting with them in a realistic way. Constitutive modelling aims at defining a proper mathematical law able to reproduce the response of a geomaterial specimen under any loading condition, either mechanical or non- mechanical (e.g. chemical). The group working on this topic has a long tradition (Nova (1977), Nova ad Wood (1979), Nova (1992), di Prisco et al. (1993)). In recent years, the emphasis was put on modellling sand liquefaction and other types of instability occurring before ordinary failure (Nova (1994), di Prisco et al. (1995), di Prisco (1996), di Prisco and Imposimato (1996)) and on modelling the behaviour of soft rocks under mechanical loading or chemical attack (Lagioia and Nova (1995), Nova (2000)). In the reported period these two topics have been connected. The occurrence of bifurcations and instabilities such as compaction band formations or unlimited pore water pressure generation in undrained tests are in fact more likely in geomaterials with a fragile bonded structure (see e.g. Nova et al. (2003), Castellanza and Nova (2004), Nova (2006)). The problem was also tackled from a micromechanical viewpoint, by means of the discrete element method, both for unbonded and bonded geomaterials with chemically induced weathering (see e.g. Calvetti et al. (2005)). DEM was also used to investigate the behaviour of soils in triaxial and in situ tests (see e.g. Calvetti et al. (2003), Calvetti and Nova (2005)). Unconventional geomaterials with unstable structure such as snow, stabilised residues, quarrying sludges were also investigated, both from an experimental and theoretical viewpoint (see e.g. Cresseri and Jommi (2005), Nova (2006)). Experiments were also conducted in collaboration with the University of Naples to investigate the behaviour of granular materials under cyclic and dynamic loading, with the goal of determining the influence of various loading factors. A multiple mechanism modification of an existing elastovisco- plastic constitutive model (di Prisco et al. (1993)) was proposed to take into account the observed phenomena. The multiple mechanism model has been implemented in a spectral element code (GeoELSE) and some numerical analyses have been carried out.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Full Professors
Roberto Nova
Claudio di Prisco
Associate Professors
Cristina Jommi
Francesco Calvetti
Assistant Professors
Riccardo Castellanza