A hybrid structure to protect infrastructures from high energy rockfall impacts

The need of structures able to stop large moving blocks requires impact mechanics studies coupled with capacity design. Among natural phenomena, rockfall probably is the most hazardous due to its abruptness and high ener-gies involved. Rock blocks can impact a structure even with a kinetic energy of 50 MJ, developing extremely large forces and involving consistent damages. To protect inhabited areas and infrastructures, mitigation measures are installed along slopes. Focusing on protective measures, several solutions can be adopted, i.e., net fences, embankments, rigid barriers, etc. Such structures intercept and stop the falling block by dissipating its kinetic energy through permanent large deformations. The performances of the systems are different and depend on the adopted technology. Net fences with dissipators can stop blocks up to 10000 kJ, but they need large downslope free area. RC walls alone are not diffused as they cannot withstand rockfall impact forces. Although reinforced earth embankments are a profitable solution for the high capacity (up to 50 MJ), their geometry repre-sents a strong constraint because of large width and heavy weight. We propose a compelling solution for pro-tecting infrastructures with a hybrid structure made of multiple vertical layers: a high deformable downhill earth face coupled with a RC wall. This solution ensures energy dissipation and reduced deformability of the downslope face of the structure and can be installed close to roads. A simplified design procedure and an exam-ple are proposed with reference to a real case study. The effectiveness of the rockfall risk mitigation measures is discussed and a cost-energy capacity design chart is presented.