Effect of the foundation soil properties on the optimum design of reinforced concrete retaining walls and defining critical boundary lines

Abstract

The optimum design of reinforced concrete retaining wall (RCRW) is among the common optimization problems in civil engineering as it is affected by many different failure modes and input parameters. The properties of the foundation soil are one of the most critical input parameters in the optimum design of the retaining wall, just as in other civil engineering structures. While the existing foundation soil conditions on the site may sometimes be sufficient for an optimum design or it is necessary to consider alternative solutions such as ground improvement or foundation type change. This paper aims to determine the effects of the shear strength parameters of the foundation soil on the optimum wall cost using the modified artificial bee colony algorithm. For this purpose, optimum designs were performed separately for a total of 9246 different shear strength parameter combinations for a wide range, where the cohesion parameter was also considered in addition to the internal friction angle only used in the literature. The analysis results showed that the shear strength parameters of the foundation soil are highly influential in wall costs under weak soil conditions but not under strong soil conditions. In order to make this distinction easier, three important cost regions and two boundary lines separating these regions were defined depending on the shear strength parameters of the foundation soil, and an approach was proposed to determine the positions of these boundary lines. Moreover, the 125 wall models were investigated under 9246 different foundation soil conditions to reveal the effects of important parameters such as wall height, surcharge load, and backfill internal friction angle on the critical boundary lines. Knowing the boundary lines separating weak and strong soil conditions depending on the wall input parameters will significantly contribute to the truly optimum design of retaining walls.