An 11 m high dry-stacked masonry concrete block wall reinforced with a high-density polyethylene (HDPE) geogrid was designed, instrumented, and monitored for a period of 2 years as part of a highway-widening project southeast of Seattle, Washington, in the USA. An extensive materials-testing program was conducted to characterize the geogrid and backfill soil properties. The empirical-based K-stiffness method was used to design the wall, and this approach resulted in a 35% reduction in total required reinforcement strength compared with the American Association of State Highway and Transportation Officials / Federal Highway Administration (AASHTO/FHWA) simplified method. The cost savings more than compensated for the cost of the instrumentation program. Geogrid strains were measured using strain gauges and extensometers, and the walls were surveyed to monitor facing deformations. The stiffness of the geogrid materials was computed from the results of laboratory in-isolation constant-load (creep) tests. The time- and strain-dependent stiffness values, in combination with measured strains, were used to compute measured reinforcement loads at the reinforcement connections and at locations within the reinforced soil backfill. The measured loads were compared with class A, B, and C1 predictions using the AASHTO/FHWA simplified and K-stiffness methods. These comparisons demonstrate that the simplified method significantly overestimated reinforcement loads, whereas the K-stiffness method provided estimates that were judged to be in better agreement with the measured results. The paper also quantifies the influence of construction procedures on reinforcement strains and load, shows that long- term creep of the reinforcement after 2 years after construction is negligible, and identifies lessons learned. Key words: geosynthetics, walls, stresses, strains, design, soil reinforcement, simplified method, K-stiffness method, hyperbolic isochronous model. Un mur en maconnerie de 11 metres de haut, fait de blocs de beton places sec et renforce d'une geogrille en polyethylene de haute densite (HDPE), a ete concu, instrumente et suivi sur une periode de 2 ans. Ce mur faisait partie d'un projet d'elargissement d'une autoroute au sud-est de Seattle, Washington, aux Etats-Unis. Un vaste programme d'essais sur les materiaux a ete realise afin de caracteriser les proprietes de la geogrille et du sol de remblayage. La methode de rigidite K, basee sur des lois empiriques, a ete utilisee pour concevoir le mur et cette approche a permis de reduire de 35 % la resistance en renforcement totale requise comparativement a celle requise selon la methode simplifiee de l'American Association of State Highway and Transportation Officials / Federal Highway Administration (AASHTO/FHWA). Les economies en argent ont plus que compense pour le cout du programme d'instrumentation. Les deformations de la geogrille ont ete mesurees a l'aide de jauges de deformation et d'extensometres, tandis que le mur a ete instrumente pour mesurer les deformations de la face. La rigidite des materiaux de la geogrille a ete obtenue a partir des resultats d'essais de laboratoire a charge constante en isolation (fluage). Les valeurs de rigidite dependantes du temps et des deformations, combinees aux deformations mesurees, ont ete utilisees pour calculer les charges de renforcement mesurees aux connections de renforcement et aux endroits a l'interieur du sol de remblayage renforce. Les charges mesurees ont ete comparees aux predictions de class A, B et C1 obtenues avec les methodes de l'AASHTO/FHWA simplifiee et de rigidite K. Ces comparaisons demontrent que la methode simplifiee surestime significativement les charges de renforcement, tandis que la methode de rigidite K offre des estimations qui sont jugees plus en accord avec les resultats mesures. Cet article quantifie aussi l'influence des procedures de construction sur les deformations et charges de renforcement, demontre que le fluage a long terme du renforcement 2 ans apres la construction est negligeable, et identifie les lemons apprises. [Traduit par la Redaction] Mots-cles: geosynthetiques, murs, contraintes, deformations, conception, renforcement du sol, methode simplifiee, methode de rigidite K, modele hyperbole isochrones., Introduction An 11 m high masonry-block geosynthetic-reinforced soil wall (wall C) was constructed at a highway project located southeast of Seattle, Washington, in 2005-2006. A 6.3 m high companion wall [...]