Site classification is the key to a successful design, however it is fraught with uncertainty, partly because of the economics of house construction. The classifier must use judgement and available knowledge to classify a greenfield site. Then there are earthworks to consider, which may alter the classification. Designers need to be aware of the risks and the possible variability of Characteristic Surface Movement (ys) estimates, or the levels of classification provided. The role of the structural engineer is to provide a suitably stiffened and integrated raft slab, or in some circumstances, an isolated piled footing system, to meet minimum serviceability requirements adopted by Standards Australia, AS 2870. Beam layout and reinforcement detailing are critical. The design approach in the Standard originated in the 1970s and has not been improved since for routine design. However there exist finite element programs, which allow more sophisticated modelling of footing systems. The availability of finite element programs is limited to academics and some consultants. Past experience with finite element modelling of footings and lessons learned from this modelling are discussed. In order to be meaningful, the models must employ basic soil-structure-interaction and allow reduction of the stiffness of concrete sections.
About Dr Don Cameron
Don has a world-wide reputation on the performance of building foundations in reactive soils. Through publications and CSIRO reports, much of his research was adopted by the Australian Standard for residential footings (AS2870). Don has chaired the South Australian Footings Group and the Australian Geomechanics Society (SA chapter) for an extensive period. On the national level, he has chaired the Australian Standards committee for footing design and construction through a major revision, which was issued in 1996. He has been on this Standards committee since 1986. Internationally he was a member of Technical Committee TC106, Unsaturated Soils for the International Society for Soil Mechanics and Geotechnical Engineering from 2011 to 2014, and TC202, Transportation Geotechnics, from 2011. Accordingly, Don is often called upon to lecture on site classification and footing design. He is also called upon to give advice on damaged buildings. Don has published over 110 publications which include the disciplines of geotechnical engineering and pavement engineering.
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