Balancing pipe

[kechha2060]

I have a mile long road with ditch on both side. 4 x-culverts are proposed which are tend to act as a balancing resorvoir (max 60" pipe d/s). Will there be any problem since the culverts will be submerged for few days (3-4 days) before the water is finally let go through flap gates. culverts have head walls. will the roadway structural integirity be compromised? any other problem that might happen in the future??

 

[cvg]

keep the water surface elevation below the bottom of the roadway subgrade. make sure ditch slopes are flat enough to be stable when saturated. If you have expansive clay soil, this might be a problem.

not sure I understand why you would use flapgates on the x-culverts, that might prevent equalization. are the flaps on the outfall?

 

[kechha2060]

yes the flap gates are at the outfall.

 

[TerryScan]

Another issue of concern is subsequent storm events. In my location, it rains, on average, one out of three days. If your practice takes 4 days to drain what happens if another storm event occurs? (Here, they like to see a storage facility drain within 48 hours).

 

[cvg]

over 3 feet deep, this would require a fence and next to a road, would probably require a barrier also for safety

 

[kechha2060]

My concerns is pipe leaking and leading to piping action. In major flood event, the roadway will be shut down. guard rail is specified. No such criteria as how long to drain. will have to hold water until the level in stream come down n release thru flap gates).

 

[cvg]

without relatively high pressures or velocities, "piping" is not likely to occur. With most ditches and culverts, it is not a big risk. None the less, I would recommend gasketed joints to prevent leakage