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A Framework for Subsidence Practitioners to Optimise the Benefits and Practical Use of Root Barriers to Resolve Clay Shrinkage Subsidence and Prevent the Unnecessary Loss of Valuable Trees

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posted on 2023-08-30, 19:40 authored by Graeme Allen
Context-Tree-related subsidence is a concern in Britain on cohesive clay soils, with significant costs incurred by insurers every year to rectify the resulting property damage. Tree removal is the preferred solution as it is relatively inexpensive, eliminates the cause, and prevents re-occurrence. However, there is increasing evidence highlighting the importance and value of trees, especially within urban environments such as reducing the effects of climate change, improving health and wellbeing, enhancing wildlife and crime reduction for example. Aims-This thesis investigates the root barrier solution as an alternative to tree removal. Root barriers comprise a physical barrier installed, up to 5m deep, between the tree and the building thus preventing tree roots from reaching the foundations thus resolving clay shrinkage subsidence without removing the tree . Regarding the root barrier solution, the literature review identified very little published information on deeply embedded root barriers to resolve tree-related subsidence and no published guidance for practitioners. The research fills the gap and aims to promote root barriers by considering costs, value for money, practical and knowledge concerns culminating in a design protocol for practitioner use. Method Qualitative and quantitative data was used to research the practical use of root barriers alongside surveys within a post-positivist theoretical perspective. The mixed-method approach collected data from over 30 case studies combined with responses from informed practitioners using structured questionnaires. Findings-Based on the analysis, root barriers are shown to be a viable and cost effective solution to tree-related subsidence. The research found that root barriers are cost-effective where multiple or large trees (over 500mm diameter) are involved in subsidence claims. The new design protocol produced from this study provides guidance for practitioners to design root barriers. Further research in construction techniques and materials would be beneficial to overcome practical difficulties. Ultimately, because of this research, deciding whether to use root barriers will be more informed, preventing the unnecessary loss of valuable trees.



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