Optimization of Design of Column-Reinforced Foundations

The design of foundations on soft ground reinforced by columns usually involves two important verifications, namely, checking for adequate bearing capacity and checking for acceptable settlement performance. This paper details a comprehensive methodology for determining the optimized portion of the ground area that should be improved by the installation of columns. The optimization is required to avoid an overly conservative design and, consequently, the use of uneconomical quantities of material to construct the columnar reinforcement. The basis of the suggested methodology consists of first estimating the minimum improvement area ratio (IAR) required to ensure attainment of the required design bearing capacity of the reinforced soil and then determining an upper-bound or maximum value of IAR by considering the issue of allowable settlement. Optimization is then performed on the IAR within the range defined by these bearing capacity and settlement limits. Analysis of three case studies provides an illustration of the implementation of this novel design methodology, which has been incorporated into software recently developed to assist in the design of soil foundations reinforced by columns and to provide cost-effective solutions for this type of foundation.