Uma abordagem à modelação de solos não saturados

Os geomateriais das camadas dos pavimentos e das vias-férreas, bem como os das respectivas fundações, encontram- se no estado não saturado nas boas condições de serviço destas infra-estruturas. Torna-se por isso necessário considerar o aspecto não saturado destes materiais na modelação e no dimensionamento destas infra-estruturas. O presente artigo propõe a generalização do conceito de tensão efectiva para solos não saturados. De modo a descrever o comportamento exibido pelos solos não saturados, nomeadamente os fenómenos de colapso durante a humidificação, é proposto um modelo elastoplástico. Este modelo, descrito em termos de tensões efectivas, é calibrado para o caso de uma areia siltosa com base em resultados de ensaios triaxiais clássicos e de precisão com medição da pressão intersticial negativa

Using a non linear constitutive law to compare Menard PMT and PLT E-moduli

Engineers may now be bewildered by the various values of E-moduli they can get on the same soil if they are not aware of the variability of such a modulus with the strain level that the soil sustains. Today using simple softwares as Plaxis 7 may help a lot to understand the degradation of the E value when the strain level increase. In this paper we compare the strain levels of the soil for the pressuremeter tests, the plate loading test and the tri-axial test. Using a non linear elastic plastic constitutive law (usually known as exhibiting isotropic strain hardening) we were able to find a good agreement between the various E-moduli obtained in these different tests

Comparaison des modules de déformation obtenus par essais de chargement à la plaque et essais pressiométriques

Trop souvent l‘ingénieur est confronté à la disparité entre es valeurs des modules mesurées lors d’un chargement de plaque et au cours d’un essai pressiométrique Ménard. Ces résultats peuvent être comparés à l’aide d’une interprétation par retro-anaIyse mettant en jeu une Ioi de comportement du sol éIasto-pIastique hyperbolique. On met alors en évidence l‘importance de a prise en compte du niveau de déformation associé aux deux types d’essais.Too often the design engineer is facing discrepancy between E-moduli values obtained from pate Ioad tests and prebored pressuremeter tests. Results of these two types of tests can be compared by using a back analysis involving an hyperbolic elastic plastic constitutive Iaw. It appears that the strain level associated with each test is one of the factors which makes the difference.LCPC, ENPC, Presses de l’Ecole Nationale des Ponts et Chaussé

Dynamic analysis of rail track for high speed trains: 2D approach

In the framework of an ongoing national research project involving the University of Minho, the National Laboratory of Civil Engineering and the New University of Lisbon, different commercial FEM codes (DIANA, PLAXIS and ANSYS) were tested to model the dynamic performance of a high speed train track. Initially a plain strain model is considered in a robin test using experimental data from a well documented instrumented standard ballast rail track under the passage of a HST at 314 km/h. Numerically predicted results are presented and assessed, and comparison is made between the different codes and also the experimental data.The authors are acknowledge the financial support for this research from the Foundation for Science and Technology (FCT) (project POCI/ECM/61114/2004 - Interaction soil-railway track for high speed trains)