Are 1 FT thick retaining walls really needed in the construction of Bioretention Basins?

[Riversidean]

Hello Everyone!

Has anyone been successful in not implementing a Caltrans Retaining Wall Type 1A into their Bioretention Basins structures as a sort of separation barrier between the bioretention basin and existing soil material? Although my local NPDES district seems to consider a 1 foot thick, steel reinforced concrete retaining wall enclosure as standard for the construction of at ground level bioretention basins it seems like over kill to me. There will be soil on both sides of the retaining wall so there should be similar forces on both sides of the structure. Perhaps a thinner structure simply to separate the bioretention soil from the existing soil? 4" Thick Shotcrete with wire mesh? Or maybe even a plastic geomembrane? Thoughts?

Regards,

Riversidean

 

[Kevin_Engineer]

I've worked in communities that implement them as a decorative separation when integrated in the urban section, but with standalone basins that take drainage from yards (aka surrounded by grass, not pavement), I've put them in with no liner or block.

However, the soils I've installed then in are usually clayey, so I put an underdrain in the section. In sand areas, I've had success wit out an underdrain when infiltration rates allow. I guess it depends on the structure of your soil, but it's definitely possible to put them in without a wall or other separator.