City of Salisbury

Street trees project

The City of Salisbury has supported applied research into the effects of street trees on pavements since the year 2000. Currently the City, along with the Local Government Association, is sponsoring postgraduate research into the suitability of street trees on expansive clay sites. Aaron O'Malley's PhD research is summarised below:

The combination of Adelaide’s (the capital city of South Australia) reactive soils and the prevailing semi-arid climate means that houses and pavements must withstand significant underlying soil movements. Trees in an urban environment can add to these movements and the patterns of deformation. As trees are an environmentally desirable part of urban streetscapes, a field trial was initiated to study the ground movement patterns in streets on extremely reactive ground, with an expected movement in excess of 100 mm, in a new suburb of Adelaide. The major objective of the study is to establish movement patterns prior to street trees becoming established, in order to provide a benchmark for future movements that may arise as the trees mature and gardens become established. Ultimately the research will impact on the design of footings.

Six sites have been established within the development for monitoring soil moisture changes to six metres depth near street trees, away from the trees and below the street. The raft slab footings of nearby masonry veneer houses have been surveyed and will be re-visited in the future. Regular level surveys of the ground surface at each site are being undertaken. Information on deeper movements are obtained from a ground movement station. The suitability of different street tree species is also being studied to aid future planning and development.

Areas of study and research

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