Investigation of geosynthetic reinforced tiered retaining walls using finite element analysis

Tiered reinforced soil retaining (RSR) walls can be used to take advantage of both the aesthetics and the economics of RSR walls while considering high heights. In such walls, an offset between each pair of adjacent tiers is introduced, thus reducing the displacements and increasing the factor of safety. This study was divided into two parts and in both of the parts a commercial computer program Plaxis 8.2 which is based on finite element method is used to conduct totally 58 analyses. In the first part of the study; effects of reinforcement length (L), type of reinforced soil and offset distance between tiers (S) on the behaviour of two tiered reinforced soil retaining wall was investigated using numerical analyses.Increasing reinforcement length causes increase in factor of safety and decrease in the horizontal displacements. However; when offset distance exceeds 1.5 times the tier height, effect of reinforcement length on factor of safety and displacements decreases significantly. Increasing the offset distance increases the factor of safety and reduces the permanent horizontal displacements as expected. For the chosen soil types; when cohesive fill used instead of non cohesive fill, lower safety factors and higher displacements in magnitude were obtained. Second part of the study was conducted to determine the critical offset distance beyond which two tiered wall behaves like two independent walls. For non cohesive fill, critical offset distance was found as 2 times of the tier height (2H). When cohesive fill was used, this value was 2.25 times the tier height (2.25H).