Design Procedure
The design procedure for gabions is as follows. It uses the same roughness relationships developed for riprap.
Step 1. Determine channel slope, channel shape, and design discharge.
Step 2. Select a trial (initial) mattress thickness and fill rock D50, perhaps based on available sizes for the project. (Also, determine specific weight of proposed stone.)
Step 3. Estimate the depth. For the first iteration, select a channel depth, di. For subsequent iterations, a new depth can be estimated from the following equation or any other appropriate method.
As with riprap linings, the ability to deliver the expected channel protection depends on the proper installation of the lining. Additional design considerations for gabion linings include consideration of the wire mesh; freeboard; proper specification of gradation and thickness; and use of a filter material under the gabions.
The stability of gabions depends on the integrity of the wire mesh. In streams with high sediment concentrations or with rocks moving along the bed of the channel, the wire mesh may be abraded and eventually fail. Under these conditions the gabion will no longer behave as a single unit but rather as individual stones. Applications of gabion mattresses and baskets under these conditions should be avoided. Such conditions are unlikely for roadside channel design.
|
