Carmine Gerardo Gragnano presented a paper to investigate the failure mechanisms of modular block geosynthetic reinforced soil (GRS) retaining wall using finite element analysis, and won the student award competition at EuroGeo6. This paper presented a numerical study to investigate the effect of reinforcement vertical spacing and reinforcement length on the internal stability of GRS retaining walls, including failure modes of reinforcement breakage and reinforcement pullout. In the numerical analysis, the backfill soil was simulated using a nonlinear hyperbolic model to account for the stress-dependent soil stiffness. The geogrid was simulated using elasto-plastic elements that can only sustain tensile forces. The numerical model also considered the interaction between different components using interface elements. Strength reduction method was used to investigate the internal stability of GRS retaining walls, in which the reinforcement ultimate tensile strength was reduced to check the reinforcement breakage failure mode and the soil-reinforcement interface shear strength was reduced to check the reinforcement pullout failure mode. For the reinforcement breakage failure mode, the factor of safety for a GRS wall with a reinforcement vertical spacing of one-block-height is three times that for a GRS wall with a reinforcement vertical spacing of two-block-height. Reinforcement pullout was observed for the GRS walls when the soil-geogrid interface strength was reduced to 21% of the initial strength for reinforcement length = 0.7H (H = wall height) and to 15% of the initial strength for reinforcement length = 0.9H. Simulation results in this study indicate that reinforcement vertical spacing has a more important effect on reinforcement breakage, while reinforcement length has a more important effect on reinforcement pullout.
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Reported by Yewei Zheng, IGS Young Members Chair for the North American Region.