Evaluation of a simplified soil constitutive model considering implied strength and pore-water pressure generation for one-dimensional (1D) seismic site response.

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Date: July 2020
From: Canadian Geotechnical Journal(Vol. 57, Issue 7)
Publisher: NRC Research Press
Document Type: Article
Length: 10,226 words
Lexile Measure: 1640L

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Abstract :

Pore-water pressure (PWP) generation can lead to soil softening and liquefaction of sandy soils during earthquakes, with potential influence on site response and seismic design. The authors evaluated the generalized quadratic/hyperbolic (GQ/H) constitutive model, which captures small-strain stiffness, large-strain shear strength, and is coupled with a widely used cyclic strain-based PWP generation model (termed GQ/H+u). A suite of cyclic direct simple shear tests with a range of relative densities (~30%-80%) and effective vertical stresses (~25-200 kPa) and dynamic centrifuge tests with liquefiable sands were used to evaluate the ability of the GQ/H+u model to simulate cyclic soil behavior. Results indicate that GQ/H+u provides reasonable estimates of PWP increase during cyclic shear, with differences between measured and computed excess PWP ratios ([r.sub.u]) for both element and centrifuge tests generally smaller than 0.1. Computed spectral accelerations are comparable to centrifuge test measurements, with almost no bias at medium to long periods (T 0.4 s) when the computed maximum shear strain ([[gamma].sub.max]) was smaller than the limit shear strain ([[gamma].sub.limit]). When computed [r.sub.u] 0.8 and computed [[gamma].sub.max] [[gamma].sub.limit], spectral accelerations may be underestimated at both short and long periods as dilative behavior is not captured by GQ/H+u. Key words: site response analysis, effective stress analysis, DEEPSOIL, liquefaction, pore-water pressure generation. La production de pression d'eau interstitielle (PEI) peut entrainer le ramollissement du sol et la liquefaction des sols sablonneux pendant les tremblements de terre, avec une influence potentielle sur la reponse du site et la conception sismique. Les auteurs ont evalue le modele constitutif generalise quadratique/hyperbolique, qui saisit une faible rigidite a la deformation et une resistance au cisaillement a forte contrainte, et qui est couple a un modele de generation de PEI cyclique largement utilise (appele GQ/H+u). Une serie d'essais de cisaillement cycliques directs simples avec une gamme de densites relatives (~30-80%) et de contraintes verticales effectives (~25-200 kPa) et d'essais dynamiques en centrifugeuse avec des sables liquefiables ont ete utilises pour evaluer la capacite du modele GQ/H+u a simuler un comportement cyclique des sols. Les resultats indiquent que GQ/H+u fournit des estimations raisonnables de l'augmentation la PEI pendant le cisaillement cyclique, les differences entre les rapports de PEI excedentaires (ru) mesures et calcules pour les essais sur les elements et en centrifugeuse etant generalement inferieures a 0,1 Les accelerations spectrales calculees sont comparables aux mesures des essais en centrifugeuse, avec presque aucun biais sur des periodes moyennes a longues (T 0,4 s) lorsque la contrainte de cisaillement maximale calculee ([[gamma].sub.max]) etait inferieure a la contrainte de cisaillement limite (7Umit). Lorsque [r.sub.u] calcule 0,8 et que [[gamma].sub.max] calcule [[gamma].sub.limit], les accelerations spectrales peuvent etre sous-estimees a court et a long terme, car le comportement de dilatation n'est pas saisi par GQ/H+u. [Traduit par la Redaction] Mots-cles : analyse de la reponse du site, analyse des contraintes effectives, DEEPSOIL, liquefaction, generation de pression d'eau interstitielle.
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Gale Document Number: GALE|A629397468