Water extraction by isolated trees and its possible impact on building foundations on clay soils

Spatial and temporal variation in soil water content and bulk density was measured near Melaleuca and Ulmus trees, with neutron and gamma gauges, on a Duplex soil in Melbourne, in order to examine water extraction patterns of these trees and foundation movement arising from water extraction. The experiment simulated the situation of isolated trees growing on city pavements. Results indicated that both trees extracted similar amounts of water. However, Ulmus, the exotic, deciduous species, extracted water from a greater depth near the tree than Melaleuca, the Australian native, evergreen species. Melaleuca extracted water from a greater distance than Ulmus. Data on bulk density indicated differential swelling and shrinkage of greater magnitude near Ulmus than Melaleuca, although seasonal shrinkage adjacent to Melaleuca was higher than Ulmus. The results are discussed in relation to variation in compressibility factor of overburden and damage to building foundations.

Postconstruction settlement of an expressway built on peat by precompression

This paper presents the analysis of 18 years of settlement observations of two expressway embankments built on a peat deposit with an initial depth of 3.0–5.8 m using the precompression technique. Observations show that upon removal of the temporary surcharge the highway embankments heaved for about 1 year by a total of 4.3–7.9 cm. This foundation movement was followed by slow-rate settlement for a few years and subsequently by additional secondary settlement occurring at a greater rate of settlement versus logarithm of time. Eighteen years after construction, settlements range from 2.7 to 11.9 cm. It is concluded that precompression has been effective in reducing postconstruction settlement by about 65% and its effectiveness on the long-term settlement was experienced for [Formula: see text] years. After that, the rate of settlement became identical to that of the normally consolidated peat. Key words: peat, precompression technique, secondary compression, long-term settlement, field observation, swelling, surcharge.