Numerical studies on two-tiered MSE walls under seismic loading

Mechanically Stabilized Earth (MSE) retaining walls, reinforced by the geogrids and using rigid segmental blocks as facing elements have extensively been used in recent past as an economic and sustainable solution for the earth retention. Nevertheless, in the case of a high retaining wall, tiered walls are preferred than a single-tier retaining wall due to their cost-effectiveness and more stability than single-tiered MSE walls. However, the behavior of tiered MSE retaining wall under dynamic loading is not yet studied thoroughly as the conventional design in practice is based on offset distance between the tiered walls and certain assumptions of surcharge loading imparted by the weight of tiered walls itself. Therefore, an attempt has been made to examine the behavior of tiered MSE retaining wall using finite element method, having a height of 12 m (H) under gravity and seismic loading to compare its stability with the conventional (single-tier) MSE retaining wall in terms of factor of safety (FOS) and to look into the possible modes of failure. The factor of safety shows a raise of 66% in two-tiered walls, when the horizontal seismic acceleration coefficient ( k h ) is 0.36 for both the walls, during the analysis of single-tiered and two-tiered wall systems. An optimum reinforcement length is evaluated for two-tiered wall system under seismic and static loading conditions. It is suggested that reinforcement 0.8H and 1.1H is suitable in two-tiered MSE walls, under static and dynamic loading respectively.