Passive Drapery Systems

Basic Concept

Drapery systems are used to mitigate the effects of rockfall without preventing it. This system aims to control the descent of falling rock by limiting the velocity/energy gained during descent.

High Tensile Steel Mesh is used to provide a curtain, beyond which the falling rock cannot pass. Upon detachment from the face, the loose rock will impact on the mesh curtain and then rebound onto the rock face, each time dissipating energy and preventing high velocities from developing.

Drapery systems utilise bolts at the crest and optionally at the toe of the rock face through which the load imparted onto the mesh, ensuring transferred back into the face. Wire ropes running along the crest and toe are used to hang the mesh ensuring loads are distributed over more than one anchorage point.

The primary installation focus of drapery systems is to ensure that the mesh remains as close to the face as possible, following the contours of the slope. Any area where the mesh comes away from the slope offers room for rock to free-fall and gain energy. Fast moving rock can deflect from the face and potentially punch through the mesh; drapery systems are best suited to even and relatively smooth faces.

Drops of drapery mesh should be terminated with an opening at the toe and a rock trap or ditch whenever possible, to allow for the failed material to be removed. In some cases, this will not be possible; therefore, the amount of strain in the mesh, when under load, is important to prevent encroachment into the site at the toe, e.g. lanes of traffic.