Reclaiming Deep Quarry Lakes in South Florida – A Geotechnical Perspective-Paper

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The paper examines geotechnical challenges in redeveloping former quarry lakes in South Florida, where shallow groundwater and decades of limestone and sand extraction have left deep artificial lakes and potentially compressible bottom sediments.<br /><br />At Site A, a 200-acre lake proposed for backfilling, preliminary sediment conditions were assessed cost-effectively using bathymetric and sub-bottom geophysical surveys, diver probing, and sampling. Most of the lake bottom appeared to have 1–3 feet of mainly non-plastic silty sand or sandy silt, though localized areas may be thicker. Laboratory testing evaluated mixes of quarried shot-rock, fine cyclone sand, and organic muck. Results favored including 10–30% cyclone sand and limiting muck to about 10–15%; higher muck content reduced density and strength. Loose-placed mixes had low bearing resistance, indicating that ground improvement would still be needed. More detailed exploration is recommended after backfilling.<br /><br />Site B, a 110-acre lake already filled primarily with processed construction debris, was investigated using borings. Beneath the thick fill, a soft, compressible depositional silt layer averaged about 10 feet thick and posed a significant settlement risk. Deep dynamic compaction and other alternatives were considered inadequate or uneconomical for addressing the deep silt. Preloading was selected to consolidate the silt and compress the fill before construction. Surcharges of 18 feet beneath warehouse footprints and 5 feet in paved areas produced substantial settlement during preparation—about 30–40 inches beneath warehouses and 5–10 inches in paved areas. Settlement generally stabilized within one to two months after surcharge placement ended.<br /><br />The cases show that lake-bottom conditions, fill composition, stress distribution, and settlement must be evaluated early. Controlled reuse of quarry byproducts and construction debris can reduce costs, but requires testing and appropriate ground improvement. Preloading proved an effective method for reducing long-term settlement risk.

Keywords

geotechnical engineering

quarry lake redevelopment

South Florida

compressible sediments

bathymetric survey

sub-bottom geophysical survey

backfilling

cyclone sand

preloading

settlement risk