Settlement characteristics of deep engineered fills

Peter J. Waddell and Patrick K. Wong


The long-term settlement characteristics of engineered fills are generally not a significant concern where the fill thickness is less than a few metres. With the increasing scarcity of land for urban and commercial development and the availability of large volumes of excavation materials, sites are being considered for development that previously would have been filled with refuse of other uncontrolled material and left undeveloped. For such sites, including backfilled quarries, the long-term settlement characteristics of the fill becomes an important consideration.

In this paper the settlement of engineered fill has been characterised as having four potential components:

  1. Short-term Settlement, which occurs due to self-weight as the fill is placed and for a relatively short time after fill has reached full height.
  2. Elastic Settlement, which occurs in the fill when subjected to loads from footings and floor slabs.
  3. Long-term or Creep Settlement, which occurs over a period of years. In the case of deep fills with light building loads, the creep due to the self-weight of the fill will be the major component of the long-term settlement.
  4. Hydroconsolidation (Collapse) Settlement, which can occur and is due to saturation of the fill.

This paper presents data on the settlement characteristics of deep fill with emphasis on the characteristics of engineered fill (i.e. fill placed and compacted in relatively thin layers to an engineering specification).

Data derived from laboratory testing and field monitoring is provided for a variety of materials placed as deep engineered fills for a number of projects in the Sydney Region.

Settlement estimates derived from parameters obtained from a desk study of international literature and some data from the Sydney Region are presented and compared with the results of more recent laboratory testing on materials from the Sydney Region.