Segmental Retaining Wall for Detention Pond

[LOTE]

I am designing a segmental block retaining wall that forms the walls of a dry detention pond. My scope is just the retaining wall design. One side of the pond will act more like a "dam" with the backside of the wall sloping down. See attached cross section sketch (assume this is not to scale...). The wall is roughly 5-ft tall.

I plan to have the typically 12" of clean gravel behind the blocks and to design the wall for rapid drawdown. What type of fill would you spec out for the rest of the reinforced zone and the retained zone along the slope? Should this be an impermeable material to prevent seepage?

How would you design for the negative slope?

The owner has not hired a geotechnical engineer yet, but it will be a requirement for me to design the wall. What things should I notify the owner to ensure is in the geotech's scope, and what questions should I pose to the geotech?

 

[Jrit]

We do these occasionally, and typically spec a silty sand with less than 45% passing. A bit more silty material will probably be put behind it as there is plenty of that material in our area and it's not much of a wall. You'd want a relatively low permeability but typically the pond should discharge relatively quickly. IMO, if the material works for a pond berm, it will work for this wall. We wouldn't worry about the negative slope as long as you can get your grids in and the design is sufficient for the hydrostatic pressure.

Regarding the geotech's scope, I'd see it as needing all the normal info to design a segmental wall. Unless this is a high visibility project with a very low risk tolerance (typically in our market it would not be), I don't see this being much different than a normal 5-foot wall.

 

[LOTE]

Thanks Jrit! You confirmed a lot of my assumptions.