Tree-integration into flexible rockfall barriers: feasibility, implementation and structural design

Society has established different mitigation strategies to minimize rockfall impacts on civil infrastructure. Typically, there are two distinct active protection measures to minimize the impact of natural mountain hazards: protection forests as a natural solution and rockfall barriers as a technical solution, which are applied when the protective effect of the natural solution is not sufficient. These measures have usually been implemented separately without the consideration of combined solutions. This study, guided by the approach of nature-based solutions, offers a strategy to permanently implement trees into rockfall barriers. It includes the tree-physiological potential impact forces, the technical design, and the structural dimensioning. We assessed the force-absorption potential of trees based on literature research. The technical design developed during this study is based on pre-existing tree-integrated systems (TIS) and various fixation strategy suggestions. We aimed for our structural engineering dimensioning to be according to the European Guidelines for designing steel and timber structures. The literature shows that there is stem breakage in cases of sudden dynamic impacts like rockfalls, but no uprooting is observed. As a result, the potential impact force was determined solely by the wooden body, which was dimensioned in accordance with European guidelines. This detailed dimensioning strategy results in an innovative TIS design. E.g., in the case of a 50 m long 500 kJ barrier, 6 steel posts, and 11 drilled anchors can be saved, assuming the use of 35 cm thick trees. The designed TIS rockfall protection system would be feasible and structurally sound up to energies of 1000 kJ if thicker trees were used.