RCP Design - (height of fill to use when designing on a slope)

[CWEngineer]

Are there any requirements for the selection of the height of fill above an reinforced concrete pipe when the pipe is beneath a sloped ground surface? I assume, you would design the pipe for the maximum height of fill, minimum height of fill and 2 feet of fill. However, I am not sure if you would need to use a particular height to capture the height of fills between your max and min heights. Believe some agencies use 10 ft to capture fills below 10 ft for box culverts, but not sure if this is applicable to reinforced concrete pipes. Appreciate your advice.

 

[MotorCity]

There are a few things to consider:

1. Minimum fill may be controlled by local frost depth

2. A minimum height of fill may be required to safely transmit surface loads to the pipe. The intensity of a load at the ground surface typically decreases with depth (in a triangle or pyramid shaped distribution). Depending on the capacity of your pipe, a minimum depth may be required to disperse the load.

3. Design would be governed by a minimum fill height specified by the agency or the actual max fill height

4. The additional 2' of fill requirement is typically used to account for any sort of construction or vehicle traffic instead of trying to calculate various vehicle loads and wheel arrangements.

 

[cvg]

you don't "select" the height of fill. You design the pipe for whatever fill and other loads are placed on it. The invert elevation and height of fill is usually set by the hydraulic design, not by structural. If you want to economize, you can vary the D-load along the length in order to reduce cost. However, unless you have a large project with a lot of pipe, it is best to just pick the worst case loading and specify that all pipe must meet the strength requirement for that condition. It becomes very difficult for the contractor to install and the inspector to verify that correct class or d-load pipe is installed in every location. It is also unlikely that the manufacturer will want to produce several different classes of pipe. Many owners just require Class III minimum, everywhere unless otherwise specified.