Continuum modelling of expansive soil using sensors network

Expansive or reactive soils are clay soils that experience substantial volume change due to periodic drying and wetting, further influenced by seasonal and climatic variations. This volume change eventuates as swelling upon wetting and shrinkage upon drying (Sun, 2015). Such ground movements can create differential movement in footings, resulting in cracks and damage to light structures. Many countries in the world, including Australia, the United States, Israel, India, and South Africa, have reported infrastructure damage problems due to the movement of expansive soils (Li, Cameron et al., 2014). The problems are particularly significant in Australia as 20% of the surface area is covered by expansive soils (Richards, Peter et al., 1983) categorised as moderate to highly expansive clays with an imposed damage potential extending from minor cracking to irreparable damage to buildings. Quaternary basalt clays generally exhibit expansive characteristics and are commonly found in the Western parts of Melbourne, where the case study sites in this thesis have been chosen. In Australia, the design of residential foundation slabs constructed on expansive soil is based on the guidelines of Australian Standard AS2870: 2011 wherein the ground surface movement, ys is estimated and a site class is defined based on the characteristic surface movement, and footing design will be based on the site class. This procedure provides a discrete value over the design life, whereas the changes in soils are hugely sensitive to seasonal changes and environmental influences. Consequently, a continuum approach to modelling the above effects is required and is addressed in this thesis. Two field sites were established to collect high-quality suction data. Watermark soil sensors that can measure changes in soil suction were placed at depths ranging from 0.3 m below ground up to 1.5 m. Daily data obtained were used to analyse the suction variations monthly. This instrumentation provided an improved understanding of the physical processes driving the volume change of expansive soil at the case study site. Various climate parameters were also monitored from the nearby weather station. Displacement profiles of a mound slab were also monitored at these sites. Using the diffusion-advection model proposed by Venkatesan, Droniou et al. (2021) diffusion and advection coefficients for the two sites were investigated. A new statistical approach to quantify the variations of suction subjected to seasonal influence and its dependency on diffusion-advection coefficients has been investigated in this thesis. Using these values, suction profiles were simulated using a MATLAB code, and the ground movements were obtained using the two-dimensional finite element approach based on Abaqus/Standard. A continuum approach to modelling site-specific surface movement has been presented for both the case study sites. The predicted results compare favourably with the field results. Appropriate model validation and calibration are also presented in chapters 4,5,6, and 7. This research provides a robust prediction of soil suction changes and ground movement at a given site based on a continuum approach. This work will significantly assist the footing design procedure given in AS2870: 2011 and the practitioners. It includes field monitoring, laboratory tests, numerical modelling, and case study. The outcomes of this study have added valuable information to predict the volume change behaviour of expansive soil, therefore contributing to a higher level of understanding of the behaviour of unsaturated soil. Further improvements and validations of the above approaches are recommended in the concluding parts of the thesis.