The use of steel nets or netting is one of the most widely practiced mitigation methods for rockfall throughout the world, particularly for controlling high-frequency, low-magnitude rockfalls on small to medium sized slopes. The type of nets or netting used and the support configuration is dependent on the intended outcome of mitigation as well as the physical characteristics of the site and rockfall events. There are two primary systems types: draped and anchored systems.
Draped Mesh Systems
A draped mesh system, sometimes known as simple drapery, consist of nets or netting that are supported by a bearing rope system anchored to the brow of a slope. The mesh is draped across the slope in a manner to maximize the slope contact. The slope is allowed to erode behind the mesh layer, which acts as a barrier to control the movement of debris as it progresses down the slope, often into a catchment ditch at the toe.
The most important material parameters to consider for design are the unit weight, tensile strength and puncture strength. As the need to control larger debris increases, so does the need to increase the strength of the draped mesh system.
Slope Retention Systems
Slope retention systems, also known as anchored mesh systems, consist of nets or netting anchored to the slope using a dense matrix of soil or rock anchors and specialized anchor plates. The anchor spacing and placement is determined by the anticipated failure mode and potential mass of material mobilized. The system is designed to resist the loads and retain the material in situ.
The most important material parameters to consider for design are the tensile strength and puncture strength. A common mistake is to specify the tensile strength of an individual wire but this has no relevance to system design.