Asphalt pavement is comprised of three main layers: top, base and subbase. The top layer, the strongest layer, is designed to distribute the traffic loadings to the base and then to the subbase, the weakest layer.
Asphalt pavement can be categorized as two major types: FDA pavement and conventional asphalt pavement. The major difference between the two types is, the former has asphalt within the top and base layers while the latter has asphalt only within the top layer. The subbase layer for both types is compacted dirt and the base for the conventional pavement is fully compacted limerock material.
Regardless of the type, asphalt pavements are designed with sufficient strength to counter traffic loading. One major parameter in the design of asphalt pavement is the proximity of the water table to the bottom of the base, what is commonly referred to as base clearance. The base clearance is the vertical distance between the bottom of the base layer and the Seasonal High Ground Water Table (SHWT). As the base clearance decreases, so does the strength of the pavement.
In low lying areas, where the SHWT is at 1-3 feet from the surface, the construction of pavement becomes very challenging due to difficulties in achieving the compaction require for the compacted dirt and limerock material. Florida Department of Transportation (FDOT) Pavement Design Manual recognizes this as major problem. As a result, FDOT recommends the use thicker asphalt layers. Such case occurred with the Alton Road reconstruction project between 5th Street and Michigan Avenue where FDA was provided for the entire corridor due to the reduced base clearance (just below 2.5 feet in average).
In the recent report prepared by Jacobs Engineering with respect to the road elevation strategy, Jacob’s recommendation for the pavement design is consistent with the FDOT Pavement Design Manual with the evaluation of different design options performed by the engineer responsible of the pavement design for each specific roadway project.
Specifically, Jacobs recommends that when the base clearance is 1 foot or higher throughout the 30 year design life (accounting with the Sea Level Rise and increasing depth of SHWT), then FDA may be unnecessary. However, if the base clearance is less than 1 foot, then thicker asphalt layers may need to be evaluated.
Results from the 2019 Resident Survey show that 50% of residents rated capital improvements completed by the City as very satisfied/satisfied. In order to continue maintaining excellent standards in this area, the City is open to receiving resilience initiatives for consideration.