Case Study of Ground Subsidence Caused by the Drying Effect of a Group of Australian Native Eucalypts

Abstract

Expansive clay soils are subject to considerable volume changes due to seasonal variations in soil–water content. Its shrink–swell characteristics can lead to differential movements, which can cause damage to lightly weighted structures and pavements. The damage can be severe with the presence of trees, as the root system would take a significant quantity of water from the soil, resulting in restricted shrinkage settlement. This paper presents a case study of tree-root-induced subsidence and cracks in the surface of a netball court located in an eastern suburb of Melbourne, Australia. A geotechnical investigation was conducted, and four boreholes were drilled close to and sufficiently away from a group of Australian native Eucalypts (Corymbia maculata). The daily water use of the selected tree was monitored using a sap flow instrument. The soil suction and water content profile were developed based on the measurement results, indicating that the severe soil drying developed at 1.5 m below the surface of the netball court, where the soil was the driest up to 1.0 m located approximately 7.6 m from the tree group. A contour map was delineated based on the level survey carried out around the cracking surface of the court, and the results revealed that the crack is most likely attributed to the soil settlement caused by the drying effect of tree roots.