Imaging and monitoring tree-induced subsidence using electrical resistivity imaging

Tree-induced subsidence is a natural ground movement phenomenon that arises when tree roots absorb water from clay-rich soils, causing them to shrink. Tree-induced subsidence is particularly problematic for buildings and structures in close proximity to deciduous trees where changes in seasonal climate can have a significant effect on the degree of relative surface movement. Unfortunately, there is a lack of in-depth understanding of tree-induced subsidence dynamics and limited access to affordable/reliable assessment technologies for the victims of such phenomena. This paper presents and discusses the use of 2D electrical resistivity imaging (ERI) as a tool for recognizing tree-related subsurface desiccation and its associated subsidence. The findings of a two year ERI study in a high-risk tree-induced subsidence environment are presented (mature Oak and Willow trees growing in expansive London Clays) where repeat (time-lapse) resistivity profiles are compared to conventional ground levelling and soil moisture content data. This study confirms that ERI is a valuable tool for the characterization of seasonally varying subsurface moisture distributions and that the technique is capable of defining the architecture and temporal-spatial variance of an active tree root system. Moreover, the method provides a critical insight into the visualization of tree-induced subsidence phenomena and reveals promising practical potential for use as a modern, affordable, non-invasive tree-induced subsidence assessment tool.