Abstract

Foundation built on layered soil is often encountered in the field. Layered-soil profile could
be either a natural or artificial phenomenon. For structures with large footing dimensions two
layers of subsoil are usually involved in the determination of bearing capacity of soil. Also,
building of heavy structures on weak soils often needs a blanket of granular material to cover the
natural soil and increase the soil bearing capacity. In fact, the granular layer both distributes and
alleviates the load pressure due to the infrastructure. Popular weighted average method and
projected area method fail to predict accurately the soil bearing capacity when the upper layer is
dense sand.
This thesis investigates the bearing capacity of strip footings on a layer of dense sand
underlined by loose sand. The effects of thickness and shear strength of top layer as well as the
embedment depth of footing were investigated. A numerical model was developed to predict the
bearing capacity of footing on layered sand. The results showed that the bearing capacity of strip
footings on dense sand (with friction angle, φ, higher than 40 degrees) with and without
embedment depth is overestimated by weighted average method and is underestimated by
projected area method. Comparison with the available theory and experimental result are
presented. It is of interest to report herein that, in the absence of surcharge the footing bearing
capacity from numerical analysis was always less than Hanna (1981). In the presence of the
surcharge load due to the embedment depth of footing, the results were close to that obtained by
Hanna (1981).