Influence of trees on expansive soils in Melbourne

In Australia, distortions of residential buildings caused by tree drying settlement have been widely reported, particularly in areas of expansive or reactive soils. The paper presents the results of two major projects dealing with trees and expansive clay soils in the Melbourne Metropolitan area. The first project is the long-term field study of the effects of trees on the performance of a building, soil moisture patterns and ground movement in basaltic clay. The second project is a case study of a residential house damaged by expansive soil movement due to tree root drying. In this field study the sap flow rate of a tree was seen to be closely correlated with solar radiation. It was also observed that the soil moisture content profile near the tree was significantly lower than that away from the tree. The findings of the second study clearly indicated that trees, growing in close proximity to a house could cause more severe damage to the buildings than the expected moisture changes due to seasonal effects and re-distribution of soil moisture arising from construction on the site.