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: A method for simulation-based steering of the mechanized tunneling process in real time during construction is proposed. To enable real-time predictions of tunneling-induced surface settlements, meta models trained a priori from a comprehensive process-oriented computational simulation model for mechanized tunneling for a certain project section of interest are introduced. For the generation of meta models, Artificial Neural Networks (ANN) are employed in conjunction with Particle Swarm Optimization (PSO) for the model update during construction and for the optimization of machine parameters to keep surface settlements below a given tolerance. To provide a rich data base for the training of the meta model, the finite element simulation model for tunneling is integrated in an automatic data generator, for setting up, running and postprocessing the numerical simulations for a prescribed range of parameters. Using the PSO-ANN for the inverse analysis, i.e. identification of model parameters according to monitoring results obtained during tunnel advance, allows the update of the model to the actual geological conditions in real time. The same ANN in conjunction with the PSO is also used for the determination of optimal steering parameters based on target values for settlements in the forthcoming excavation steps. The paper shows the performance of the proposed simulation-based model update and computational steering procedure by means of a prototype application to a straight tunnel advance in a non-homogeneous soil with two soil layers separated by an inclined boundary.Tunnelling and Underground Space Technology 10/2014; · 1.59 Impact Factor
- Geoshanghai 2014; 05/2014