Perforation of flexible rockfall barriers by normal block impact

J. P. Hambleton*, O. Buzzi, A. Giacomini, M. Spadari, S. W. Sloan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Flexible rockfall barriers are a common form of protection against falling blocks of rock and rock fragments (rockfall). These barriers consist of a system of cables, posts, and a mesh, and their capacity is typically quantified in terms of the threshold of impact (kinetic) energy at which the barrier fails. This threshold, referred to here as the "critical energy," is often regarded as a constant. However, several studies have pointed out that there is no single representative value of critical energy for a given barrier. Instead, the critical energy decreases as the block size decreases, a phenomenon referred to as the "bullet effect." In this paper, we present a simple analytical model for determining the critical energy of a flexible barrier. The model considers a block that impacts normally and centrally on the wire mesh, and rather than incorporate the structural details of the cables and posts explicitly, the supporting elements are replaced by springs of representative stiffness. The analysis reveals the dependence of the critical energy on the block size, as well as other relevant variables, and it provides physical insight into the impact problem. For example, it is shown that bending of the wire mesh during impact reduces the axial force that can be sustained within the wires, thus reducing the energy that can be absorbed. The formulas derived in the paper are straightforward to use, and the analytical predictions compare favorably with data available in the literature.

Original languageEnglish (US)
Pages (from-to)515-526
Number of pages12
JournalRock Mechanics and Rock Engineering
Issue number3
StatePublished - May 2013


  • Analytical
  • Bullet effect
  • Finite element
  • Impact
  • Kinetic energy
  • Rockfall barrier

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Geotechnical Engineering and Engineering Geology
  • Geology


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