Performance of kaolin-tire derived aggregate mixture as a backfill material for retaining wall

Abstract

Backfill material for retaining wall should be lightweight in order to reduce the lateral pressure behind the wall. In addition, high permeability backfill walls are designed to eliminate or minimize the development of pore water pressure. Tire Derived Aggregate (TDA) has low unit weight and high permeability. Moreover, reutilizing solid wastes like TDA with cohesive soil as backfill material may reduce sand mining and preserve the environment to achieve sustainable construction. Therefore, the aim of this study was to evaluate the performance of Kaolin-TDA mixtures as a backfill material for retaining wall. Geotechnical properties of Kaolin, TDA and Kaolin-TDA mixtures were determined in addition to compaction and hydraulic conductivity tests. A total of 13 scaled down 1:20 physical model tests on polymer concrete retaining wall using Kaolin and different mixtures of Kaolin-TDA as backfill material were performed. Footing settlements and wall displacements due to loading on fabricated steel as strip footing in the model test were measured. The results were verified using three numerical methods, namely PLAXIS 2D, Genetic Programming and Multiple Linear Regression. The maximum dry density of Kaolin- TDA mixture was in the range of 964 kg/m3 to 1590 kg/m3, lighter than the maximum dry density of Kaolin 1750 kg/m3. Therefore, using Kaolin-TDA mixture as backfill material reduced the unit weight of backfill in a range of 9% to 45% resulted in a decrease in lateral pressure. Physical modeling and permeability tests results showed that mixture of Kaolin with 20% Granular (5-8 mm) TDA was the optimum mixture. The permeability of the optimum mixture was 2.56 times higher than that of the Kaolin. It was also observed from the physical modeling that by using the optimum mixture as backfill material, it resulted in footing stress roughly 3 times higher than using Kaolin without TDA. Thus, by mixing TDA with Kaolin, the weight of backfill decreases, permeability increases and footing stress increases compared to Kaolin as a backfill material for retaining wall.