Gabion basket retaining wall & existing CMP culvert interface

[Squad3]

Hi all,

I am looking at constructing a gabion basket retaining wall along a rural portion of a roadway at a stream crossing. The stream has an existing 72" tall x 106" wide elliptical culvert to convey flow under the roadway. The gabion basket wall would be utilized to help with some slope erosion and to limit the amount to grading (trying to keep within existing road right-of-way). The existing culvert would extend beyond the proposed location of the gabion basket walls (approx 10' on the upstream side and 7' on the downstream side). My issue is that due to the size of the culvert, I can not construct a concrete headwall to the existing culvert. How would the gabion baskets interface with the culvert? Would I detail "custom" baskets (in a trapezoidal shape)? Or is there a flange (angle iron) type of attachment to the culvert to prevent soil migration from between the baskets and culvert? Any help information would be greatly appreciated. Thanks in advance!

 

[gbam]

What is prohibiting the concrete headwall, cost, size or what? Have you considered mitering the pipe to slope and using gabions to protect the slope?

 

[Squad3]

A concrete headwall was considered but determined to be infeasable due to the width of the existing culvert (10') and the likelyhood of havign to divert/reroute the stream. Constructibility would be an issue. Headwall construction would likely disturb the existing stream bed, there are several environementally sensitive areas downstream. In addition, a DEQ (Departemnt of Environmental Quality) permit would be required which would create severe delays in the project timeline. Current reviews are running 6-8 months.

 

[gbam]

Squad3 - Wouldn't there be a need for a DEQ permit for the gabions within the stream? There is still disturbance within the stream for gabions. Have you considered other options? I remember seeing a corrugated steel headwall in Mo. some years back. You may want to contact Contech or some other cmp mfr.

Can you post a plan and profile of the pipe? I am thinking that If you set the headway back from the end of pipe your work would be out of the existing stream. Use BMPs to proctect the stream, just a thought.