CASM: a unified state parameter model for clay and sand
ABSTRACT The purpose of this paper is to present a simple, unified critical state constitutive model for both clay and sand. The model, called CASM (Clay And Sand Model), is formulated in terms of the state parameter that is defined as the vertical distance between current state (v, p′) and the critical state line in v–ln p′ space. The paper first shows that the standard Cam-clay models (i.e. the original and modified Cam-clay models) can be reformulated in terms of the state parameter. Although the standard Cam-clay models prove to be successful in modelling normally consolidated clays, it is well known that they cannot predict many important features of the behavior of sands and overconsolidated clays. By adopting a general stress ratio-state parameter relation to describe the state boundary surface of soils, it is shown that a simple, unified constitutive model (CASM) can be developed for both clay and sand. It is also demonstrated that the standard Cam-clay yield surfaces can be either recovered or approximated as special cases of the yield locus assumed in CASM.The main feature of the proposed model is that a single set of yield and plastic potential functions has been used to model the behaviour of clay and sand under both drained and undrained loading conditions. In addition, it is shown that the behaviour of overconsolidated clays can also be satisfactorily modelled. Simplicity is a major advantage of the present state parameter model, as only two new material constants need to be introduced when compared with the standard Cam-clay models. © 1998 John Wiley & Sons, Ltd.
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ABSTRACT: Landslides induced by rainfall represent a significant natural hazard for large part of Europe. The catastrophic flowslides that occurred on steep slopes in Campania (southern Italy) in 1998, 1999, and 2005 were triggered by rainwater infiltration into shallow deposits of pyroclastic soils, which were initially unsaturated. In this work we present a back analysis at two different scales on the effects of infiltration into a layer of pyroclastic soils. The evolution of pore water pressure, water content and displacement has been monitored at laboratory scale in a flume test and in situ in the Cervinara slope located North-East of Naples. In the back analysis of flume test, a fully hydro-mechanical model has been used to describe the behaviour of the pyroclastic soils from unsaturated to saturated condition. In the case of Cervinara slope, the soil-atmosphere interaction has been modelled as a boundary fluxes which take into account the thermo-hydro-mechanical interaction based upon fundamental physics.Procedia Earth and Planetary Science. 01/2014; 9:222–228.
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ABSTRACT: Behavior of rockfills was investigated experimentally and theoretically. A series of standard triaxial compression tests were carried out on a quarried rockfill material at different stress levels. It was found that both the stress level and the shear stress ratio, like most of granular materials, controls the behavior of rockfill materials. At lower shear stress ratios the behavior is much more similar to a nonlinear elastic solid. When the shear stress goes further, the stressstrain curve shows an elasto-plastic behavior which suggests using the disturbed state concept to develop a constitutive model to predict the stress-strain behavior. The presented constitutive model complies reasonably with the experimental data.Frontiers of Structural and Civil Engineering. 6(4).
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ABSTRACT: The effectiveness of an environmentally friendly stabilising agent for soil, namely, lignosulfonate was examined through a series of laboratory tests. A simple bounding surface plasticity model was developed to capture the bonding effects induced by lignosulfonate. One of the appealing aspects of the model is that it can incorporate the mechanical behaviour of the bonded soil during shearing, including the brittle and ductile failure modes. Validity of the model was verified by experimental results of lignosulfonate-treated soils under different stress path conditions. The mechanical behaviour of chemically treated soil was adequately captured by the model.Computers and Geotechnics 09/2014; 61:316–327. · 1.65 Impact Factor