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The paper describes load and resistance factor design (LRFD) calibration for the resistance factor used in the Stiffness Method internal stability soil failure limit state for geogrid mechanically stabilized earth (MSE) walls. The Stiffness Method was recently adopted in the current American Association of State Highway and Transportation Officials LRFD Bridge Design Specifications in the US, and will appear in the next edition of the Canadian Highway Bridge Design Code. The paper describes the details of the calibration of the soil failure limit state which is unique to the Stiffness Method. Calibration outcomes include consideration of the concept of level of understanding in the selection of nominal load and resistance values which is unique to LRFD foundation engineering practice in Canada. A practical conclusion from these calculations is that if product line- specific creep test data are available to estimate the reinforcement secant creep stiffness used for design, then a resistance factor of 1.0 is reasonable for US practice. If only minimum average roll value tensile strength data are available, then a value of 0.95 is recommended for US practice. For Canadian practice, the corresponding values for typical level of understanding are 0.90 and 0.85, respectively. Key words: stiffness method, soil failure limit state, mechanically stabilized earth (MSE) walls, geosynthetic reinforcement, geogrid, load and resistance factor design (LRFD), Introduction The Stiffness Method is used to calculate the maximum tensile loads in geosynthetic and steel reinforced mechanically stabilized earth (MSE) walls under operational conditions (AASHTO 2020a; Allen and Bathurst [...]

This paper demonstrates reliability-based design (RBD) and analysis for tensile strength (rupture) and pullout limit states for mechanically stabilized earth (MSE) walls constructed with steel grid reinforcement in combination with frictional soils. Five different reinforcement tensile load models for walls under operational conditions are considered in combination with six different pullout models and one tensile strength model. The general approach considers the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty in the choice of nominal values at the time of design that is linked to the concept of 'level of understanding' used in Canadian load and resistance factor design (LRFD) foundation engineering practice. The effect of potential steel corrosion on reliability index for the tensile strength limit state is considered in calculations. A well-documented MSE wall case study is used to demonstrate the general approach. The relationship between nominal factor of safety and reliability index is used to demonstrate how to optimize steel grid member diameters and arrangement to achieve a target reliability index of [beta] = 2.33. The approach described in this paper is an important contribution to next-generation analysis and design using modern concepts of RBD for MSE walls. Key words: reliability-based design (RBD), mechanically stabilized earth (MSE) walls, steel grid reinforcement, internal stability limit states. Cet document demontre la conception basee sur la fiabilite (CBF) et l'analyse de la resistance a la traction (rupture) et des etats limites d'arrachement pour les murs en terre stabilisee mecaniquement (TSM) construits avec un renforcement de grille en acier en combinaison avec des sols de friction. Cinq modeles differents de charge de traction des armatures pour les murs dans des conditions operationnelles sont consideres en combinaison avec six modeles d'arrachage differents et un modele de resistance a la traction. L'approche generale tient compte de la precision des modeles de charge et de resistance qui apparaissent dans chaque equation d'etat limite plus l'incertitude dans le choix des valeurs nominales au moment de la conception qui est liee au concept de << niveau de comprehension >> qui est utilise dans la pratique canadienne d'ingenierie des fondations en matiere de conception des facteurs de charge et de resistance (CFCR). L'effet de la corrosion potentielle de l'acier sur l'indice de fiabilite pour l'etat limite de resistance a la traction est pris en compte dans les calculs. Une etude de cas bien documentee sur le mur des TSM est utilisee pour demontrer l'approche generale. La relation entre le facteur nominal de securite et l'indice de fiabilite est utilisee pour demontrer comment optimiser le diametre et la disposition des elements de la grille en acier afin d'atteindre un indice de fiabilite cible de [beta] = 2,33. L'approche decrite dans ce document est une contribution importante a l'analyse et a la conception de la prochaine generation utilisant les concepts modernes de CBF pour les murs des TSM. [Traduit par la Redaction] Mots-cles : conception basee sur la fiabilite (CBF), murs en terre stabilisee mecaniquement (TSM), renforcement de la grille en acier, etats limites de stabilite interne., 1. Introduction This paper is focused on reliability-based design (RBD) and analysis for tensile strength and pullout limit states of steel grid-reinforced mechanically stabilized earth (MSE) walls constructed with frictional [...]

This paper demonstrates reliability-based design for tensile rupture and pullout limit states for mechanically stabilized earth (MSE) walls constructed with geosynthetic (geogrid) reinforcement. The general approach considers the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty due to the confidence (level of understanding) of the designer at the time of design. The reliability index is computed using a closed-form solution that is easily implemented in a spreadsheet. The general approach provides a quantitative link between nominal factor of safety, which is familiar in allowable stress design practice, and reliability index used in modern civil engineering reliability-based design practice. A well-documented MSE wall case study is used to demonstrate the general approach and to compare margins of safety using different load and resistance model combinations. A practical outcome from the case study example is the observation that the pullout limit state is much less likely to control design than the ultimate tensile rupture state for walls with continuous reinforcement coverage. The more accurate 'simplified stiffness method' that is used to compute tensile loads in the reinforcement under operational conditions is shown to generate a more cost-effective reinforcement option than the less accurate American Association of State Highway and Transportation Officials (AASHTO) simplified method. Key words: mechanically stabilized earth (MSE) walls, geosynthetic reinforcement, internal stability limit states, reliability-based design. Cet article demontre une conception basee sur la fiabilite pour les etats limites de rupture en traction et darrachement pour les murs de terre stabilises mecaniquement (<>) avec un renforcement geosynthetique (geogrille). L'approche generale considere la precision des modeles de charge et de resistance qui apparaissent dans chaque equation d'etat limite plus l'incertitude due a la confiance (niveau de comprehension) du concepteur au moment de la conception. L'indice de fiabilite est calcule a l'aide d'une solution analytique facilement implementee dans une feuille de calcul. L'approche generale fournit un lien quantitatif entre le facteur de securite nominal connu dans la pratique de la conception des contraintes admissibles et l'indice de fiabilite utilise dans les pratiques de conception basee sur la fiabilite du genie civil moderne. Une etude de cas MSE bien documentee est utilisee pour demontrer l'approche generale et pour comparer les marges de securite en utilisant differentes combinaisons de modeles de charge et de resistance. Un resultat pratique de l'exemple de l'etude de cas est l'observation selon laquelle l'etat limite d'arrachement est beaucoup moins susceptible de controler la conception que l'etat de rupture en traction ultime pour les murs a couverture continue. La methode de rigidite simplifiee la plus precise utilisee pour calculer les charges de traction dans le renforcement dans des conditions operationnelles est montree comme generant une option de renforcement plus rentable que la methode simplifiee << American Association of State Highway and Transportation Officials >>(AASHTO) moins precise. [Traduit par la Redaction] Mots-cles : murs de terre stabilises mecaniquement (MSE), renforcement geosynthetique, etats limites de stabilite interne, conception basee sur la fiabilite., 1. Introduction The internal stability design of mechanically stabilized earth (MSE) walls in North America is most often based on load and resistance factor design (LRFD) which is a reliability [...]

The paper presents the numerical modelling details using the finite difference method (FDM) to simulate the performance of a well-instrumented geogrid-reinforced incremental concrete panel soil retaining wall. Two different constitutive models were investigated for the backfill soil (linear elastic-plastic model and nonlinear elastic-plastic model). Both constant stiffness and strain-dependent secant stiffness models were used for the reinforcement elements. The paper provides valuable lessons to modellers to simulate the performance of this type of earth retaining structure. For example, parametric investigation of the effect of a constant Young's modulus ranging from 40 to 120 MPa for the linear-elastic Mohr-Coulomb model had only minor influence on the wall facing displacements and reinforcement loads. However, the choice of magnitude of transient compaction pressure near the facing can result in large differences in facing displacements. The paper also demonstrates that the method of construction including the location, sequence, and stiffness of the temporary supports used to construct the wall plays an important role on measured and predicted wall performance. The physical measurements reported in this paper provide a benchmark for numerical modellers to verify other numerical models for walls of the type investigated here. Key words: geosynthetics, numerical modelling, instrumented wall, incremental panel facing, geogrid reinforcement, FLAC. Le document presente les details de modelisation numerique en utilisant la methode des differences finies (MDF) pour simuler les performances d'un mur de retenue de sol par panneaux de beton incrementaux avec une geogrille renforcee bien instrumentee. Deux modeles de comportement differents ont ete etudies pour le sol de remblayage (modele elastoplastique lineaire et modele elastoplastique non lineaire). Deux modeles a rigidite constante et a rigidite secante dependante a la deformation ont ete utilises pour les elements de renfort. L'article fournit des lemons precieuses pour les modelisateurs afin de simuler les performances de ce type de structure de soutenement de sol. Par exemple, la recherche parametrique de l'effet d'un module d'Young compris constant de 40 a 120 MPa pour le modele de Mohr-Coulomb elastique lineaire avait seulement une influence mineure sur la paroi faisant face a des deplacements et a des charges de renforcement. Cependant, le choix de la valeur de la pression de compactage transitoire a proximite du parement peut entramer des differences importantes dans les deplacements au parement. L'article demontre egalement que la methode de construction y compris l'emplacement, la sequence et la rigidite des supports temporaires utilises pour construire le mur joue un role important sur la performance de la paroi mesuree et predite. Les mesures physiques rapportees dans le present document constituent une reference pour les modelisateurs numeriques pour verifier les autres modeles numeriques pour les murs du type etudie ici. [Traduit par la Redaction] Mots-cles: geosynthetiques, modelisation numerique, paroi instrumentee, face incrementale du panneau, geogrille, FLAC., Introduction The internal stability design and analysis of geosynthetic-reinforced soil walls in North America is based on a limit-equilibrium tie-back wedge method (e.g., AASHTO 2014) that can be traced back [...]