Stormdrain system in a flat land 2

[raptorboy]

I am working on a storm drain project where the land happens to be flat, the road is a high utility corridor, there are strick cover restrictions (I.E. I need a foot from the top of the pipe to the bottom of the AB but there is only three feet of ground to work with and the road section is 2 feet thick.) and the grades of the storm drain pipe are probably going to be 0.5%.

I was wondering if anybody has had a similar problem. The site is very restrictive and work has to remain in the right-of-way. Most of the surface flow comes from offsite properties that have no onsite detention. There is no way to get the private properties to put detention in now so we are stuck dealing with their excess flows onto the road. The outlet channel is only 3 feet deep and the flows are so large, I would need 4 24" RGRCP at the lower elevation of the project. I could use a box culvert or eliptical as well and run them under the sidewalk. Unfortunately I need to cross the road that is to be reconstructed with a 2 foot pavement section which means there is only 1 foot for a pipe to fit in. Any suggestions?

 

[cvg]

road crossing could be made with a concrete box culvert, with traffic riding directly on the top of the box

 

[bltseattle]

For CVG's suggestion (which is a good one!), you may also want to consider the differing settlement between the asphalt and the concrete box. A concrete apron extending from the box culvert beneath the paving section can help prevent a high spot/bump from forming at the culvert location after the asphalt settles and wears for a few years.

 

[raptorboy]

Actually, we decided on the box culvert across the road. I think it will work well. We are a little concerned about reflection cracking in the asphalt around the box culvert. Thanks for the helpfull suggestions. Any more information is welcomed.

 

[TerryScan]

Aside from the beefy road section, this is a typical scenario in coastal plains.

Here, allowances are made to place pipe in the road base (higher strength pipe). Eliptial pipe is also very useful (aside from the cross section, the absense of a bell end is helpful for cover).