Rockfall and Debris Flow Barriers
Rockfall Barriers
There are several different types and manufacturers of rockfall barriers. The two main types are broken into 2 different categories, solid barriers and flexible barriers. Solid barriers can be concrete walls, block walls, earth berms, Jersey barriers, etc. Flexible barriers are engineered to catch the falling rock while dissipating the energies throughout the system to immobilize the block. When designing such a system for a specific site it is important to remember that because they are flexible systems, upon impact, they can extend several meters past the line of the posts before absorbing the energy of the falling rock. Some high energy rockfall barrier systems, may need as much as 7 meters behind the barrier as a buffer for this deflection.
Rockfall Barriers Design and Installation
In general, flexible rockfall barriers are designed with posts to hold up the barrier material, a series of top and bottom cables run through pulleys, and a braking system. The braking system helps absorb the energy from a boulder impact. System designs must take into account the expected size of the rock and the energy to be dissipated by the barrier. Barriers may be installed at the base of a rock slope allowing for a catchment area on longer slopes to stop rockfall before speed and slope angle increases the energy of a given boulder. A small foundation is typically constructed at each post, consisting of one or more anchors drilled and grouted below the planned post base. Depending on the subsurface conditions, a concrete pad may also be poured to provide a flat solid base for each post. If there is no planned maintenance of the catchment area including cleanout of rockfall, upslope cable anchors may be utilized to support the posts. If a cleanout of rockfall is expected, then barriers can be designed with support cabling all in the plane of the barrier. Other considerations include the potential for both boulders and smaller rockfalls which may require a smaller mesh to be installed on the main barrier material. Periodic barrier inspection and maintenance are highly recommended. Replacement maintenance items include braking elements, upslope cables, barrier panels, and occasionally support posts.