Min. cover on RCP
Min. cover on RCP
(OP)
A culvert we designed was installed incorrectly with only 2" of cover over the pipe. The pipe is class IV rcp. How can I verify that this will hold up to HD-50 Traffic loading?
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RE: Min. cover on RCP
But, I hardly think 2 inches of cover is appropriate.
RE: Min. cover on RCP
This is not a problem to be engineered away. This could fail at any time and somebody could get killed. Make the contractor correct this.
RE: Min. cover on RCP
Don't bother wasting your time trying to determine whether 2" of cover will be sufficient. It won't be, unless of course special installtion treatment and reinforcement is used, and then it would be cheaper to simply re-install the culvert at the design grade.
I'm curious though that you have to consider the question of the cover now? How much cover did the design originally allow for and just how tight are the drainage grade allowances for the culvert to be placed out of the contract allowable?
It doesn't quite sound like a contractor did this because generally the installaion would have failed the inspection and the contractor would be obligated or forced to install at the correct location. Was this installation done incorrectly by another party or crew, whom, for whatever reason, is not willing to undertake the repair? Or was the work not inspected propoerly and the invert elevation not checked against the gradesheet?
KRS Services
www.krs-services.com
RE: Min. cover on RCP
As an example a 18" pipe installed using a Type B trench with HS-20 loading must be class III when there is 6" of cover and class IV when there is 3" of cover. A 24" pipe in the same conditions with 3" of cover need only be class III. I have heard that some places require a class V pipe any time the cover is less than 12". This seems overly conservative but it makes it easy for the designer and reviewer to just max out the strength of the pipe and move on without doing any further calculations.
RE: Min. cover on RCP
Minimum cover is necessary to prevent excessive settlement of the backfill around the pipe and subsequent exposure of the pipe. There are two basic methods:
1) Since the soil will settle adjacent to the pipe more than over the pipe, there needs to be cover to dampen this effect.
2) There must be sufficient cover opposite a moving vehicle to resist the lateral component of the tire pressure. Even minute movement of the pipe will lead to soil settlement an exposure of the pipe.
2" in nowhere near enough. Generally speaking 9" of cover for non-traffic bearing situations is sufficient. For traffic installations a minimum of 12" should be provided.
Hope this helps
regards,
KEW
Hope this is helpfull.