Mitigation of liquefaction seismic risk by preloading

Hazard

Apport de la modélisation numérique dans l’analyse des risques sismiques liés à la liquéfaction

L’objectif de ce travail est d’étudier les effets du comportement non linéaire du sol, introduit par la liquéfaction, sur l’interaction sol-structure non linéaire lors d’un séisme en utilisant des simulations numériques. On évalue aussi l’efficacité d’une méthode de renforcement de sols dans la réduction du potentiel de liquéfaction d’un profil de sol. Les effets favorables ou défavorables de l’utilisation d’inclusions rigides dans la réponse sismique d’une structure reposant sur un profil de sol liquéfiable sont présentés. Cette analyse montre l’efficacité de la méthode à réduire la liquéfaction et par conséquent les tassements induits mais elle montre aussi que cette intervention modifie les caractéristiques dynamiques du signal à la surface et en conséquence augmente le niveau des déplacements subits par la structure

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

International audienceThe present paper deals with assessing the seismic road embankment response due to pore water pressure generation of the soil foundation. Numerical simulations are carried out so as to study the preloading technique as an improvement method to reduce 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 due to the increase of the coefficient of lateral earth pressure at rest (k o). In addition, the efficiency of the countermeasure method is limited to the cases where earthquakes produced a liquefaction zone lower than the depth of the overconsolidated soil

The effect of preloading on the liquefaction cyclic strength of mixtures of sand and silt

International audienceThe paper studies the effect of preloading on the liquefaction cyclic strength of silty sands in the free field condition. This effect first is investigated by cyclic shear tests where horizontal shear stress oscillated about a zero mean value. Samples with varying fines content and at varying pre-stress ratios, densities and vertical stresses are tested. Test results show a marked increase of the liquefaction cyclic strength with the pre-stress ratio. The effect is more pronounced for tests with less liquefaction cyclic strength without pre-stress. Using critical state soil mechanics concepts, factors simulating the effect of preloading on the liquefaction cyclic strength are identified and based on the results of the laboratory program an empirical expression is proposed predicting the increase in the liquefaction cyclic strength induced by pre-stress. This expression is validated by numerical simulation of the relevant laboratory tests using an elastoplastic multi-mechanism model. In addition, based on the derived expression, a methodology is proposed predicting the increase in liquefaction cyclic strength as a result of preloading in the field in the case of the free field condition. This methodology is validated by the comparison with field measurements on liquefaction-susceptible soils before and after the field application of preloading. Last but not least, the increase in liquefaction cyclic strength which the proposed methodology predicts for typical soil profiles and embankment preloads is predicted and discussed

Influence of Precipitates on Hydraulic Performance of Permeable Reactive Barrier Filters

International audienc

Validation of a Strategy to Predict Secant Shear Modulus and Damping of Soils with an Elastoplastic Model

International audienc

Seismic evaluation of embankment-type structures with coupled hydro-mechanical model

International audienceThe 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 (loose-to-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