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

Abstract

Society has established different mitigation strategies to minimise rockfall impacts on civil infrastructure. Two main protection measures in transit areas aim to minimize the impact of natural mountain hazards: protection of forests as a natural solution and technical solutions, such as rockfall barriers. 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 implement trees into rockfall barriers permanently. It includes the tree-physiological potential impact forces, the technical design, and the structural dimensioning. The assessment force-absorption potential of trees is based on literature research and enhanced the technical design of pre-existing tree-integrated systems (TIS). The structural engineering dimensioning follows the European Guidelines for designing steel and timber structures. Field studies show stem breakage in sudden dynamic impacts like rockfalls, but barely any uprooting is observed. Therefore, the potential impact force was determined solely by the wooden body, which was dimensioned in accordance with European guidelines. The derived and elaborated TIS design demonstrates substantial savings in materials, with the designed system proving feasible and structurally sound for energies up to 500 kJ assuming tree diameters of 30 cm. If even trees with diameters larger than 20 cm are included in the TIS, rockfall energies up to 1000 kJ can be intercepted.