Arezou Modaressi-Farahmand-Razavi

Numerical Evaluation of Earthquake Settlements of Road Embankments and Mitigation by Preloading

AbstractThis article presents an assessment of the effects of pore water pressure generation of the soil foundation on the seismic road embankment response. Numerical simulations were carried out to study the preloading technique as an improvement method for reducing the liquefaction potential and the induced settlements in a sandy soil profile. The analyses showed that the use of preloading reduces the induced settlements mostly because of the increase in lateral confinement in the superficial soil layers that results from an increase of the coefficient of lateral earth pressure at rest (ko). The research also showed that the efficiency of the countermeasure method was limited to cases in which earthquakes produced a liquefaction zone lower than the depth of the overconsolidated soil.

Constitutive model for granular materials considering grain breakage in finite deformations

Soil is subjected to shear stress and/or displacements in numerous geotechnical applications. This leads to a large number of numerical models being developed to represent its behaviour under various stress paths. This paper aims to present a sound mechanical formulation for finite strains and to introduce a rational constitutive model to match realistically the behaviour of soil where, for a high range of deformations, strains localise and the phenomenon of grain breakage is usually observed in granular soil. The reference model is the ECP’s constitutive model (also known as “Hujeux’s model”), which is an elastoplastic multimechanism model. An overview is made of laboratory results and constitutive relations that consider finite deformation, and the grain breakage phenomenon that is usually associated with it in granular materials. The performance of the proposed constitutive model is demonstrated simulating constant volume ring shear tests carried out on Ottawa (OT) and Illinois River (IR) sands up to very high shear strains and comparison of the obtained results with laboratory testing data.

SEISMIC EVALUATION OF EMBANKMENT-TYPE STRUCTURES WITH COUPLED HYDRO-MECHANICAL MODEL

The response of geotechnical structures under earthquake loading is highly nonlinear and often leads to problems of slope stability, foundation settlement and soil liquefaction. The prediction of these failure modes is a topic of great interest in geotechnical earthquake engineering, particularly for structural integrity assessment, which requires estimation of structural behavior during and after collapse. In this study, the earthquake response of a road embankment resting on a soil foundation is investigated. Both fully drained and coupled effective stress analysis are performed. Moreover, two different soil types are used for the embankment (looseto-medium and medium-to-dense sand). In the fully drained case, no failure of the embankment is observed for the medium-to-dense sand and for a certain level of ground motion. However, in the coupled effective stress simulation, for the same material and input motion, liquefaction of the foundation soil can lead to the generation of a thick shear band which produce large settlements and accelerate the failure of the embankment. The response of the loose-to-medium sand is fundamentally different, as several localization zones are generated, at the foundation part and inside the embankment body, as well. In both simulations fully drained and coupled effective stress analyis the embankment fail can occur due to shear band generation inside the embankment.