The initial exploration of the ground profile confirmed the site is underlain by expansive soils typically found in the West of Melbourne. The ground below the foundation was fully instrumented prior to pouring the slab to measure soil moisture content, temperature and ground movement at strategically varied locations.
“Our aim was to develop a clear picture of geomechanical changes occurring below the foundation with seasonal weather changes and how these affect the foundation performance. A number of sensors were installed at different locations/depths under the foundation as well as outside of it for comparison,” Dr Wasantha added.
The constructed test foundation in 2022 was monitored for more than a year, spanning through all four seasons, yielding some significant initial findings.
According to Dr Wasantha, “The covered ground below the foundation should be largely immune to surface weather changes, and the AS2870 standard also assumes mound shapes for designs defining an empirically estimated distance from the edge where the foundation could deflect due to ground movements. However, the initial first-hand data of our study disputes those empirical estimates and suggests that soil moisture content changes can extend further towards the centre of the foundation than the empirically estimated edge distance in AS2870.”
These results have direct implications for the current standard design and construction practices of residential foundations in Australia. It indicates a possible disparity between the assumptions of the standard design practice and what is actually happening on the ground.
“Our data also suggests the overall seasonal weather conditions are more influential on the soil behaviour under and in the vicinity of the foundation than the short-term weather changes such as sporadic rainfall events,” Dr Bertrand added.
Through further analyses, VU researchers have observed that surface weather changes affect the ground deeper than what is recommended in AS2870. This depth is one of the key parameters used in designing foundations. It is climate-dependent such that different values are provided in the standard for different regions and cities in Australia. There can be a multitude of factors behind the observed discrepancy.
“The soil depth undergoing shrinking and swelling due to seasonal surface weather changes has important controls on the pressure applied on the foundation. Our data suggests that this depth can be higher than that is recommended to be used in designs in AS2870 for the Melbourne region,” Dr Wasantha added.
The way forward
The current AS2870 standard is the version revised in 2011, more than a decade ago, and many environmental conditions that affect the foundation performances can be different now, caused primarily by the impacts of climate change. Based on the initial outcomes of this research, the VU researchers believe that the time has come to review the standard and materialise necessary amendments.
The monitoring of the test foundation will continue for a few more years, and the VU researchers expect to draw further insights into the short- and long-term foundation performances. They are also currently working on developing advanced software simulations, which will further shed light on comprehensively understanding the engineering performances of foundations constructed on expansive soils.
“Currently, there is a lack of datasets to develop and validate numerical models of foundations built on expansive soils. This research will produce a robust dataset for future research initiatives in this field. The simulations we are currently working on will be validated based on the observed characteristics of the test foundation and extended further for investigations in the parameter space,” Dr Wasantha said.
The research team has also embarked on using the research outputs for artificial intelligence modelling, where the foundation’s performance can be potentially predicted for the future.
As Dr Bertrand said, “The dataset of this research is also a useful resource for developing artificial intelligence models to envisage how the foundations will react to seasonal weather changes in the future. This will set a strong base for making amendments to the existing standard.”
Overall, the VU researchers are confident that the outcomes of this project will contribute to future houses being more resilient against ground movements, reducing one of the key stress points home ownership can provide.