Normally, the detention pond slopes consist of a series of poured concrete slabs, but over time water works its way underneath the slabs, eroding the subgrade. The underscour of the subgrade robs the slabs of needed support, and they begin cracking under their own weight. This cracking diminishes the detention pond’s ability to withstand erosion, leaving the structure open for containment problems.
“The detention pond area was located in an area of unconsolidated random fill that would cause cracking of the concrete slabs and fail,” explains Gary Austerman of Burns & McDowell, consulting engineer for the Army Corps of Engineers. “The soil requirements necessitated a stable material for the side slopes and bottom that would allow some settlement without failure.”