Lloveras, Baur and Stevens

Engineering Excellence Since 1956

September 2017

The Importance of Roadway Underdrains

Historically, large portions of Pinellas County, Pasco County and Hillsborough County have had a very high groundwater table, and although we seen periods of drought, the rains always return to subtropical Florida, making groundwater a problem in this area. Generally roadway base in the Tampa Bay Area is made of limerock, crushed concrete or soil cement. Limerock is very susceptible to deterioration from groundwater intrusion. If limerock is chosen as the base material, then every effort needs to be made to keep groundwater from entering this base. If the limerock does deteriorate due to the presence of water, then potholes will form in the parking lot in the affected areas. Crushed concrete is less susceptible to base deterioration, however it suffers from quality control issues due to the fact that it is made from recycled concrete. Soil cement has inherent problems as well. There is one (1) major aesthetic problem with the utilization of a soil cement road base, and that is the fact that a soil cement base will cure due to the hydration of the cement within the base, which in turn will cause shrinkage. This shrinkage effect, which is not a structural failure in this type of road base section, will create hairline cracks throughout the asphalt-wearing surface. These shrinkage cracks are the result of a natural process that occurs during the curing of a soil cement road base. These shrinkage cracks are strictly a "non-aesthetic" feature that the community residents would observe throughout this project.

Regardless of which base material is chosen, we feel that underdrains are a good investment on many sites with private roadways such as private subdivisions, condominiums and mobile home parks. The general purpose of an underdrain is to lower the groundwater that lies underneath the roadway section. The underdrain will lower the groundwater underneath the pavement and transmit the groundwater into the storm sewer drainage piping system. Underdrains under the inverted crown roads in private roadways and parking lots would allow any saturated soils under the pavement to drain and thus assist in keeping the roadway base dry.

If you have any questions, please contact one of the engineers in our Clearwater engineering firm at 727-784-3965.