Flexible rockfall barriers

Flexible rockfall barriers: a very non-linear behaviour

During impact, the large strains in the structure allow it to withstand large forces. However these large strains must not reduce the protection level of the barrier and cause overmodifications of its global geometry. To answer these apparently contradictory objectives, various systems of sliding cable and pulleys are generally used to concentrate the net around the impacted zone, while keeping the global geometry of the flexible rockfall barrier. The understanting of their mechanical behaviour thus requires to investigate the behaviour in large transformations of various nets technologies and to study the interactions with atypical boundary conditions as sliding cables. The behavior of the flexible rockfall barriers hence reveals strong geometric nonlinearities, combined with material nonlinearties for the net and for the support cables.

Development of original constitutive elements models

Technological solutions usually used for nets (woven cables and Jersey, anti-submarine nets, wire net with simple, double or triple twisting, etc.), establish a range of extremely varied solutions in which a inexpert eye can have some difficulties to choose the most adapted to a specific site. One of the objectives pursued here is to determine by homogenization the intrinsic characteristics of the mechanical behavior of these previous nets to connect them, as far as possible, to big families of membrane behavior known: isotropic, orthotropic, incompressible, etc. In parallel, a “sliding cable” element is also developped. This element is dedicated at modelling the phenomemon, called “curtain effect”,  which is characterized by the sliding of the net along the support cables, enabling the net geometrical reorganization. The modelling of these two barrier’s components is the key issue to explore the behaviour of the flexible rockfall barrier by numerical computations, which is actually the only predictive approach.

A collaborative approach

The French scientific and technical community working on issues related to landslide risks and protection devices has gathered within the C2ROP national project. The financial support provided by the national project has enabled several test programs to be carried out including quasi-static and dynamic tests on flexible rockfall barrier prototype. The results of these tests also provides an opportunity to compare the numerical calculation tools developed by the different research teams. It is a step forward to the development of reliable and effective design and justification tools.