Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Timothy Newson

Abstract

Winching tests were conducted on a mature 24-year-old Norway spruce tree. The tree was instrumented with strain gauges along the root structure and tilt sensors along the tree stem and was winched to failure. Tracked tree-root system response to failure load and the material properties of the tree-root-soil system were used to examine the applicability of simple engineering principles to tree stability analysis. Tree stability was studied using the principles of Winkler foundation model for the first time. In order to study the very complex windthrow phenomenon, a novel experimental technique was used. Tree saplings with complete structural root systems were placed in a custom built planter box fitted into wind tunnel floor and were tested to failure in the wind tunnel with clay or sand as soil media. Tree stem and roots were instrumented with strain gauges, accelerometers and high efficiency sensors. Tests were conducted with change in tree root architecture, soil and increase in wind loads. Rigorous analysis of the wind tunnel tests data gave a better understanding on dynamics of tree root soil interaction and soil root anchorage mechanics. Tree sway, damping, natural frequency and admittance estimates of tree-root system with increase in wind loading were made for the first time in this thesis. Geometric, elastic and stress similitude and dimensionless scaling parameters between the mature tree and saplings were examined. Dynamic loading and the resulting tree sapling response were analyzed in detail through rainflow technique. Static and dynamic load response was compared in detail through secant modulus of elasticity and dynamic load factor. The trenching effect on tree stability was also studied using wind tunnel testing. This study also supports the current trenching guidelines with the support of vigorous tree sapling response analysis in different soil media with increase in trenching volumes and wind load. Very different yet similar tree response was observed with change in soil media, downplaying the effect of soil strength on tree stability in windthrow research


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