Postconstruction Evaluation of Fill Compaction

Abstract

Frequently soil dry unit weight and moisture content are measured using soil samples obtained well after construction to assess whether or not fill material was properly compacted in construction defect cases. In addition to being disturbed, these samples are obtained after water infiltration, soil expansion, absorption, freeze-thaw, erosion, elevated temperatures, and/or soil hydrocompression has occurred and do not reflect the as-compacted condition. These various mechanisms usually result in an increase in moisture content and decrease in dry unit weight of the compacted fill and do not reflect the initial compaction. This paper discusses the effects of these mechanisms on postconstruction fill properties and performance, techniques for evaluating fill compaction after construction, and the importance of obtaining high-quality measurements of dry unit weight, moisture content, and relative compaction during construction to defend against poor fill compaction allegations. This paper focuses on poor compaction and hydrocompression, but other factors (e.g., precipitation, poor drainage, freeze-thaw cycles, improper foundation design, mixed foundation types, and excessive loading) also can contribute to postconstruction deformations.