Cutoff walls in Culverts

[vicky2507]

Hello

I have a general question about cutoff walls. I understand the general idea that cutoff walls prevent piping beneath a culvert. In the specific case of a culvert used to convey a brook under a road, I see the need of installing the wall in the upstream side but I can't explain why we would need it in the downstream side. Is there a reference that explains in detail the roll of cutoff walls both upstream and downstream in a culvert? I haven't found a text or a reference saying more than "they are used to prevent piping".

Thank you so much

V.

 

[bimr]

The cut-off wall is used to prevent erosion around the pipe culvert from destabilizing the pipe culvert. On the discharge side, the cut-off wall also stops erosion from occurring as the water drops out of the culvert.

HEC-14 calls for cut-off walls on both ends of the culvert.

https://www.fhwa.dot.gov/engineering/hydraulics/pubs/06086/hec14.pdf

 

[SlideRuleEra]

vicky2507 - Concur with bimr. The 1941 Portland Cement Association publication "Concrete Culverts and Conduits" is a good reference to consult for explanation of culvert design.

Downstream culvert head walls and cutoff walls are "used chiefly to protect foundations from scour in silted stream beds. A common occurrence is for erosion to start a short distance downstream from a culvert and to advance upstream, becoming more serious as it proceeds. If a head wall or cutoff extends down to firm foundation the culvert will not be endangered."

also, "Cutoff or toe walls at inlet and outlet of culverts are helpful not only in preventing scour, but also in anchoring the structure in place and in reaching firmer foundation."

Fortunately, the entire book can be read online and even downloaded (one page at a time). Here is the link:
PCA Concrete Culverts & Conduits - 1941

For convenience, I have attached the pages where the quotes given above are located.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[racookpe1978]

What I have seen several times (even here within the metro Atlanta suburban area) is water washing OVER the road bed during high rains - even without the massive hurricane or flood scenario - then causing a collapse of the whole road and culvert and both embankments (2, 3, or 4 lanes) by washout from the "downstream side" back upstream.

 

[vicky2507]

Thank you so much for your comment guys. I appreciate the references to HEC-14 and the "Concrete Culverts and Conduits" publication. This will be very useful.

Racookpe1978 thanks for the input on seeing culverts fail because of erosion or washout from the downstream side. This will definitely help me to explain the site inspector why we need that cutoff wall there. The whole issue rose because the cutoff wall is interfering with some underground pipes and he was suggesting getting rid of the wall instead of modifying the pipes. This will help me to explain the need of keeping the walls.

Cheers!

V.

 

[ACtrafficengr]

I recall my geotech professor saying that water exfiltrating from soil at the downstream end causes more erosion than infiltration at the upstream end, so if you do get piping, a downstream cutoff wall will reduce the flow velocity though the soil pores and reduce this type of erosion.

We had a contractor fail to pin the cutoff wall to the box culvert floor, and the inspector didn't catch it. After a severe storm, scour sucked the cutoff wall out from under the culvert and moved it 25 feet downstream.