Development of a simplified method for efficient assessment of tree uprooting resistance from large-deformation numerical parametric analyses on root system architecture

Background and aims

Uprooting resistance of a tree is closely related to its root system architecture (RSA), which is rather complex, diverse, and invisible from the ground surface. Conducting tree stability assessment by numerically modeling every underground RSA of millions of urban trees is prohibitive in terms of time and resources. This study aims to reveal the general root anchorage mechanism of various types of RSAs and propose a simplified method for an efficient assessment of tree uprooting resistance.

Methods

A validated truss-embedded material point model (MPM) is adopted to simulate the large-deformation uprooting process of different RSAs (i.e., tap-, plate-, heart- and sinker-shaped RSAs) and investigate their root anchorage mechanisms. A comprehensive parametric study involving 90 RSAs is performed to explore statistical correlations between RSA envelopes and uprooting resistance.

Results

The failure modes of different RSAs demonstrate a similar “cage effect” (i.e., a root-soil composite is uprooted from the ground). The uprooting resistance of trees generally contains two parts, i.e., the soil strength mobilized at the envelope of the uprooted root system and the soil weight captured by the “root cage”. The cage effect is more pronounced with an increasing root length density.

Conclusion

The proposed simplified method offers a novel way for an efficient assessment of tree uprooting resistance without a need of performing computationally-demanding MPM simulations. When root properties, soil properties, and dimensions of an RSA envelope are known, the tree uprooting resistance can be estimated.