Catálogo de publicaciones - libros

We review the governing conservation laws for three-phase partially saturated media using mixture theory including finite deformation effects and kinetic energy production. Under the assumption of barotropic flows we derive the mass balance equations in their most general form, including the compressibilities of the constituent phases. We then derive the momentum balance equations including the rates of change of linear momentum in Eulerian and Lagrangian descriptions. Next we write the balance of energy equation and illustrate the conjugate relationship of the partial stress tensor with the rate of deformation of the corresponding constituent phase. Using balance of mass and balance of momentum, we rewrite the balance of energy equation once again in an equivalent form showing the conjugate relationship of an effective constitutive stress with the rate of deformation of the solid matrix. This effective constitutive stress is analogous to Bishop’s effective stress for partially saturated soils, and to Terzaghi’s effective stress for fully saturated soils.

This paper reviews the thermo-hydro-mechanical behaviour of a cementitious porous material containing a pore space that is incompletely saturated. The incomplete saturation is interpreted in terms of the alteration of the compressibility of the fluid in the porous space rather than the presence of distinct regions of a fluid phase and a gas phase. The paper examines both the experimental and computational modelling of the heating of the plane boundary of a cylinder made of a cementitious material. The parametric evaluations of the computational results point to the appreciable influences of the near saturation compressibility effects on the thermally-induced pore pressure response within the cementitious medium.

A coupled finite element formulation for the hydro-thermo-mechanical behaviour of a water saturated and partially saturated porous material has been presented. This model is obtained as a result of a research in progress on the thermo-hydro-mechanical modelling for multiphase geomaterials undergoing inelastic strains. Numerical results of strain localisation in globally undrained samples of dense and medium dense sands have been presented. Vapour pressure below the saturation water pressure (i.e. water cavitation) develops at localisation in case of dense sands, as experimentally observed. A case of strain localisation induced by a thermal load in a sample where the displacements are constrained and evaporation takes place is also analysed.

Deformation and localization analysis is a crucial issue and has thus been intensively investigated in the last decades. In particular, geotechnical applications do not only concern a single solid material but they also affect the interaction with the pore-fluids, water and air. As a result, both the deformation and the localization analysis must be applied to a triphasic material consisting of a materially incompressible elasto-plastic or elasto-viscoplastic skeleton saturated by two viscous pore-fluids, a materially incompressible pore-liquid and a materially compressible pore-gas. Based on a continuum mechanical approach, unsaturated soil can be described within the well-founded framework of the (TPM). The numerical computations proceed from weak formulations of the momentum balance of the overall triphasic material together with the mass balance equations of the pore-fluids. The resulting system of strongly coupled differential-algebraic equations (DAE) is solved by use of the finite element tool PANDAS. Furthermore, several initial boundary-value problems are presented demonstrating the efficiency of the overall formulation.

Object-oriented (OO) methods become more and more important in order to meet scientific computing challenges, such as the treatment of coupled non-linear multi-field problems with extremely high resolutions. This two-part paper introduces an object-oriented concept for numerical modelling multi-process systems in porous media (Part 1). The C++ implementation of the OO design for process objects (PCS) as a class is described and illustrated with several applications. Due to the importance of the encapsulation of processes as individual PCS objects we denote our concept as an processoriented approach. The presented examples (Part 2) are dealing with thermal (T), hydraulic (H), mechanical (M) and componental processes (C) in bentonite materials, which are used as buDer material for the isolation of hazardous waste in geologic barriers. In particular, we are interested in coupling phenomena such as thermally induced desaturation, non-isothermal consolidation, swelling/shrinking phenomena as well as in a better understanding of the coupled, non-linear THM system.

Unsaturated soils are characterized by hydraulic hysteresis. Hysteresis can be recorded during cycles of wetting and drying. This feature isn’t accounted for in most of the classical constitutive models. In this paper, an extended Cam-clay model for unsaturated soils is applied in the Finite Element (FE) analysis of an ideal geotechnical problem. The extended Cam-clay can be coupled both with an hysteretic equation of the water retention curve (WRC) and with an “elastic” equation (i.e. the main drying curve the main wetting curve coincide). These two constitutive frameworks are adopted to model the construction stages and the impounding of an ideal dike. The differences produced by hydraulic hysteresis in the distribution of pore water pressure, displacement and stress fields are discussed.

In this study, with the distinct element method analysis in threedimensional state, simulations of the true triaxial test for spherical granular material is carried out. In this analysis, the influence of meniscus water, which is mainly cause of the complicated behavior of unsaturated soil, is expressed by introducing a constant intergranular adhesive force that acts perpendicular to the tangential plane at contact point. The influence of the intergranular adhesive force on the failure criterion and deformation are examined. From the analytical results, it is found out that not only the failure criterion but also deformation characteristic in shear process are obey to the Lade failure criterion.

A constitutive model is presented to describe the stress-strain behaviour of sand while unsaturated. The model is formulated using bounding surface theory and is presented in a critical state framework using the concept of effective stress. The model is validated against triaxial shear and oedometric compression tests. A single set of material parameters are required for the complete constitutive modelling.

A theoretical framework for modeling the elastoplastic constitutive behavior of unsaturated soils is presented. By combining the theory of mixtures with interfaces (TMI) and continuum theory of plasticity, a dissipation mechanism associated with capillary hysteresis is identified. We show that the plastic deformation of the soil matrix can be described by using a pseudo effective stress tensor. In this context the plastic deformation and capillary hysteresis are consistently simulated in a hierarchical and coupled manner. The proposed framework preserves all the advantages of those models based on the effective stress concept, two stress state variables, and mixture theory, while excluding their drawbacks.

Experimental investigations are the basis for the understanding of the soil mechanical and hydraulic properties of unsaturated soils. The requirements for the testing and measurement equipment are relatively high. Important for planning the test procedures and the development of new testing devices is having experience with saturated soils and having carried out tests under simplified conditions. In this paper, basic knowledge of soil mechanical properties of saturated fine grained and non cohesive soils are reconsidered to include some basic considerations into unsaturated soil models. The aim is to incorporate the state parameters of sand and the equivalent stress of fine grained soils. For this reason some modified approaches are presented and requirements for further experimental investigations are specified.