Numerical Analysis of Piled Raft Foundations Designed for Settlement Control on Steel Grain Silos in Collapsible Soils

Abstract

The present article assesses the potential use of piled raft foundations for settlement control in grain silos, by performing numerical analyses with instrumented structures built in a particular city of the Mato Grosso state, deep in the Brazilian agricultural frontier. In this city, eight steel grain silos were constructed, and settlements were topographically monitored. The silos were numerically back analyzed using a finite-element-based hybrid numerical tool to verify interactions influence between the isolated (unpiled) foundation rafts during the grain storage season. A parametric analysis was subsequently carried out to verify the potential use of piled rafts to decrease settlement, as well as to improve design in terms of a better configuration concerning the use of compacted soil layers beneath the raft, raft thickness and pile length, and disposition within the foundation system. The numerical analyses indicated the use of a piled raft arrangement with a geometric factor equals to 0.09 as a proposed optimized solution aiming to minimize differential and total settlements. From this arrangement onwards, changes in pile spacing, pile diameter or in the number of piles, leading to higher geometric factors, were not able to provide significant settlement reductions. The increase in raft thickness and the use of compacted soil layers do not contribute to major improvements in the foundation settlement. The alternative optimized solution was able to ensure the serviceability and safety requirements of the silos, which can serve as a design benchmark.