9.2.2 Catchment & Wire Netting

Most slopes contain small pieces of rock that could loosen in the future but do not require extensive removal or reinforcement. Catchment can consist of engineered benches, ditches, wide shoulders, berms, steel barriers, nets fences and concrete walls (Figure 2). The type of catchment to be used depends largely on site conditions, specifically the height and angle of the slope and clearance between slope and the facility.

The catchment area must be accessed periodically to remove the loose debris, which would otherwise defeat it purpose. For flatter slopes where rock falls tend to bounce and roll, a barrier is needed to deflect rocks away from the facility. Key considerations in the design of such barriers are height, location and strength.

     

Figure 2: Catchment of a rock fall in hill terrains

Wire netting over the slope face helps to prevent rockfalls from bouncing outward from the toe region. Two types of wire mesh are commonly used for this purpose: welded wire fabric and chain-link mesh.

Pinning the wire mesh to the face holds the rock in place and reduces rock removal at the toe. The pins (typically rock bolts, rock dowels, or reinforcing bars) must be strong and spaced close enough to hold large loose rocks and prevent them from dislodging and tearing the mesh.

Draping the wire mesh involves anchoring the mesh to the crest of the slope and hanging it down over face of the slope. Adjacent sections of the mesh are often either overlapped or tied together with wire. Weights, such as old tyres, concrete blocks, or timbers, may be attached to bottom of the mesh to contain rockfall in the toe region.