SUPPORT OF THE MORRIS ISLAND LIGHTHOUSE USING MICROPILES-Paper

Paper

Pdf Summary

The Morris Island Lighthouse near Charleston, South Carolina, was built in 1876 on a foundation of 264 wooden piles. A major earthquake in 1886 left the tower leaning slightly, and later harbor works caused severe erosion around the island. Once the piles were exposed to salt water and marine borers, they deteriorated, threatening the lighthouse’s stability.<br /><br />Save the Light, Inc., which acquired the structure in 1999, commissioned a foundation-preservation project. Investigations established that the lighthouse weighed about 4,400 tons and that its original piles could no longer be relied upon. The design therefore required a new support system capable of carrying the structure’s full weight. Soil borings and test piles informed the final design.<br /><br />The project installed 68 TITAN micropiles in two staggered concentric rows around the lighthouse. Each was designed for an allowable compressive capacity of 75 tons. The hollow, threaded steel rods were drilled into the soil while grout was pumped through them, creating reinforced grout columns. Load testing confirmed the design. Monitoring equipment tracked movement and tilt during construction, while the low-vibration installation method minimized risk to the historic tower.<br /><br />Because the lighthouse is offshore and exposed to weather, construction relied on a jack-up barge and careful transport of materials, including cement and fresh water. Crews worked extended shifts to finish before hurricane season. After installation, the enclosed area was filled with sand protected by filter fabric, and a permanent dock platform was built.<br /><br />Phase II was completed on July 30, 2010. The micropile system provided a practical, low-vibration foundation solution in a difficult marine setting and was intended to transfer the lighthouse’s entire load to the new supports.

Keywords

Morris Island Lighthouse

Charleston South Carolina

foundation preservation

micropiles

historic lighthouse

marine erosion

earthquake damage

soil borings

load testing

low-vibration construction