The Missing Link Multi-Use Trail project, located in Walton County, Florida, aims to construct a new multi-use trail through the Topsail Hill Preserve State Park adjacent to County Road 30A. The geotechnical investigation included three Standard Penetration Test (SPT) borings and four hand auger borings, reaching depths of up to 25 feet below existing grade. The subsurface profile primarily consists of very loose to very dense fine-grained sands and silty fine-grained sands, with varying amounts of organic material. Groundwater was encountered at depths ranging from approximately 0.5 to 3.75 feet, indicating potential impacts on construction, particularly in lower-lying areas where the boardwalk is proposed. The presence of organic materials and loose soils may pose challenges for site preparation and stability.

For the proposed boardwalk structure, a deep foundation system utilizing driven timber piles is recommended, with allowable axial compression capacities ranging from 4 tons for smaller piles to 16 tons for larger ones, depending on the size and embedment depth. The minimum embedment depth should be 10 to 15 feet, depending on the pile size. It is crucial to maintain a minimum separation of 24 inches between the base course and the seasonal high groundwater table, or 18 inches if using graded aggregate base. Site preparation should include stripping topsoil and compacting the subgrade to at least 95% of the maximum dry density, with the final lift compacted to 98%. Continuous monitoring during construction is essential to ensure compliance with geotechnical recommendations and to address any unforeseen subsurface conditions. Overall, the site is deemed suitable for the proposed construction, provided that the outlined recommendations are followed.