Shallow foundations on lightweight TDA backfill: Field tests and 3D numerical modelling

Abstract

Recent advances in tire recycling technologies coupled with increasing global environmental awareness have resulted in several new products derived from scrap tires, including tire-derived aggregate (TDA). TDA is an inexpensive engineered lightweight backfill material with excellent geotechnical properties, produced by shredding scrap tires into sizes ranging from 12 mm to 305 mm. This paper examines the performance of rigid footings resting on a surface of conventional backfill materials overlying a TDA layer. The study includes three full-scale field tests with TDA layers of different thicknesses. Based on the field tests, rigorous 3D finite element analyses (FEA) were developed to study the failure mechanism of shallow foundations over TDA. In addition, the effect on the footing performance of changing critical parameters including the TDA layer thickness, the strength of the top granular backfill, the foundation depth, the footing width, the footing shape, and subsurface soil conditions was studied. It was found that in comparison to using only conventional granular backfill, using an underlying TDA layer for shallow foundations results in a significant improvement in transferring the stresses and reducing the stress influence zone underneath the footings. For instance, before the punching shear failure in the top layer occurred, TDA was able to reduce the transferred stresses by almost one half of that by the natural backfill. Furthermore, the results of the parametric study illustrated the dependency of the bearing capacity of the spread footing on the relative thicknesses of the TDA and the top granular layers, in addition to the foundation width.