Numerical investigation of interaction mechanisms in back-to-back mechanically stabilized earth walls (BBMSEWs)

This study presents a comprehensive numerical investigation of back-to-back mechanically stabilized earth walls (BBMSEWs) under static loading conditions. BBMSEWs consist of two parallel reinforced soil walls sharing a limited backfill zone and are increasingly used in bridge approaches and transportation infrastructure, despite limited experimental data and established design guidance. Finite-element modeling using PLAXIS 2D was performed based on an ongoing bridge approach project in Iraq to evaluate the influence of key design parameters, including wall spacing-to-height ratio (W/H), reinforcement length and stiffness, and soil strength properties, on wall deformation, stability, and interaction mechanisms. Results indicate that increasing the W/H ratio leads to higher lateral displacements due to reduced confinement, while overlapping reinforcements significantly enhance system stability. A reinforcement stiffness (EA) of approximately 5000 kN/m was identified as an effective threshold, beyond which displacement reduction becomes marginal while tensile forces increase. Higher backfill friction angle and cohesion improve stability and reduce reinforcement demand. Notably, substantial lateral earth pressures persist even at zero spacing, suggesting that FHWA’s linear interpolation method may underestimate loads in stiff, low-deformation systems. These findings provide practical guidance for optimizing BBMSEW design and performance.