Estimation of Maximum Lateral Displacement of the Back to Back Mechanically Stabilized Earth Walls

Back to back mechanically stabilized earth walls (MSEWs) are the structures usually used in two sides of bridge abutments and ramps. Although this type of MSEW is commonly constructed, but limited number of design guidelines are available in this regard. According to the FHWA recommendations, if the ends of reinforcements at two sides are close enough to each other, the walls are considered as back to back for the design practice; otherwise, each wall is designed independently. In this study, considering a fixed width and height for the walls, variations of the length and vertical spacing of the geogrids, as well as friction angle of the soil, were evaluated through 196 different models built and analyzed using FLAC 2D. The critical slip surface was compared in normal and back to back conditions using limit equilibrium method. Results of modeling include lateral earth pressure behind the wall, maximum force mobilized in geogrids and lateral displacements of the wall for different cases of the study. Accordingly, it was found that maximum lateral displacement of the wall usually occurs in 0.35 to 0.57 of the wall height. Based on the maximum horizontal displacements, the recommended boundary for the two different mechanisms of MSEWs was approved. Using the maximum lateral displacements, the change in wall behavior was studied and a non-linear model with the form of power-law was developed to estimate maximum lateral displacement of the wall with respect to the governing parameters. Coefficients of determination of the analysis results for normal MSEW, back to back MSEW and both cases were calculated as 0.953, 0.969 and 0.947, respectively. This confirms the suitable accuracy of the proposed formulae to estimate maximum lateral displacements as well as the appropriate exhibition of the governing physical trends.