Mechanical stability

Mechanical models of Ailanthus altissima subjected to rock impact will be developed with both laboratory and field experiments.

The research in this task is dedicated to improve the modelling of rock impact on a tree by integrating the effects of tree crown, root system as well as specificities of Ailanthus altissima in terms of the mechanical response of both the stem and the root system. Mechanical models of Ailanthus altissima stems and root systems will be identified from laboratory and field experiments. Model parameters and their related variability will also be assessed from these experiments.

The latter phase will allow building a mixed mechanical-statistical model of impact on Ailanthus altissima, which will be used to develop a model simulating the effects Ailanthus altissima has on rock propagation at the forest stand scale. This model will further be used to relate the model parameters to ecological traits as well as the phytosanitary state of the tree.


Rockfall field experiments

To assess the stability of Ailanthus altissima to rockfall, field experiments were conducted in San Vittore (Switzerland) in spring 2016. To this end, a granite ball of 56 kg was used to simulate rockfall impacts on Ailanthus altissima. The granite ball was accelerated in a tube and hit the trees at a speed of up to 50 km/h (Fig 1). The impacts (Fig 2) were monitored with a high speed camera to calculate the maximum energy dissipation of Ailanthus altissima.

Rockfall experiment overview Rockfall experiment start
Fig. 1: A 30m long tube (left) was installed in a forest in San Vittore (Switzerland) to simulate rockfall with a granite ball of 56kg (right; © Gottardo Pestalozzi).
Rockfall experiment before impact Rockfall experiment impact Rockfall experiment after impact
Fig 2: Impact of the granite ball (from left to right) on Ailanthus altissima with a speed of approximately 50km/h (© Gottardo Pestalozzi).