Influence Of Large Gum Trees On The Soil Suction Profile In Expansive Soils

Mark B. Jaksa, William S. Kaggwa, John A. Woodburn and R. Sinclair

Trees have long been known to cause damage to residential structures and pavements, particularly when these are located in expansive soils. Often, such damage is due to desiccation of the soil as a result of the tree’s moisture demands. The onus rests on the geotechnical engineer to account for tree influences when designing footings. However, there currently exists a great need to obtain suction measurements in a variety of soil types, site conditions and tree species in order to develop robust and reliable models that account for the effect of trees on the soil suction regime. The aim of this paper is to present some recently acquired data obtained in the vicinity of a single, and a group of, spotted gum trees in highly- to extremely-reactive soils, and to discuss the implications of these data on footing design. Design suction profiles are recommended for single, large gum trees as well as a group of such trees. These profiles provide slight modifications to the profile recommended by Cameron (2001).