Soil Mixing for the SR-83 Project in Florida

SR 83/US 331 is a primary North/South roadway in Walton County that is a crucial link for tourism and commerce between the Walton County beaches and the heavily traveled I-10 corridor in the panhandle of Florida. The facility also serves as the primary hurricane evacuation route from southern Walton County. This 3.4 mile project involves expanding the current two-lane crossing of Choctawhatchee Bay to a four-lane facility to increase capacity and dramatically improve mobility within the corridor. One of the major goals of the project is to perform ground stabilization using deep and shallow soil mixing (DMM & SMM) along existing causeways. Ground stabilization was required due to the existence of moderately deep very loose soils that have settled considerably over the years. As a result, the Florida Department of Transportation (FDOT) incurred significant maintenance expenses and was unable to maintain an acceptable ride quality. The FDOT considered soil mixing as one option to control this settlement. A design was developed using a combination of SMM and DMM to transfer the loads to the more competent underlying strata. A complete field test program was performed to determine the appropriate mixes to utilize for the soil mixing given the high variability of the existing soils. Once the field test program was complete, a full scale load test along with a Plate Load Test was performed on a completed section of the South Causeway to ensure the FDOT required settlement criterion was met. The results of this test program confirmed the design assumptions and this paper will give an overview of the project with emphasis on the test program.