Modeling the cyclic response of trunk-root-soil systems under lateral loads in sand

Dynamic response of the trunk-root-soil system is pivotal under wind-induced lateral loads in vegetated regions, especially with the increasing frequency of typhoon events driven by climate change. Existing research has focused on lateral behavior of the above-ground structure of trees, with limited attention to cyclic interactions within the trunk-root-soil system. To address this gap, lateral cyclic and monotonic tests were conducted using 3D-printed model roots with two distinct architectures-tap and dichotomous-in both dry and saturated sand, representing extreme saturation conditions. The influence of field-derived factors, such as stress history, root branching, loading cycles, displacement amplitude and loading frequency, on the evolution of load-displacement behavior, along with earth or pore pressure, were revealed. Subsequently, the Cyclic Mobility model was validated through finite-element modeling to investigate cyclic response and liquefaction mechanisms within trunk-root-soil systems. It was found that the lateral resistance of trunk-root-soil systems was considerably enhanced by stress-history induced soil densification. Compared to tap roots, branched roots demonstrate slightly higher resistance but their resistance decreases more rapidly under cyclic loading due to larger residual cumulative displacement. For the tested cases, excess pore pressure around the roots typically stabilizes after fifteen cycles and decreases with depth. Notably, liquefaction in shallow soils was confirmed through model tests, with the liquefaction depth reaching 0.25 L under partially drained conditions. These results enable the integration of the lateral response of the trunk-root-soil system into the design of engineering measures for vegetated area to mitigate the impacts of typhoon and rainstorm.