When the historic Cape Hatteras Lighthouse was built in 1870, it stood 1,500 feet from the shoreline, but by late 1987 only 160 feet separated the popular landmark from the encroaching sea.
After years of analysis and deliberation, the National Park Service decided that relocation was the best option for preserving the lighthouse and its companion structures. At its new site, 2,900 feet from the original location, the tallest lighthouse in the United States and tallest brick lighthouse in the world would stand 1,600 feet from the shoreline.
International Chimney Corp. (ICC) of Buffalo, N.Y., one of only a few companies with experience in moving lighthouses, was the prime contractor. ICC hired a variety of subcontractors and consultants, including Wiss, Janney, Elstner Associates (WJE) of Northbrook, Ill., the historic architect and masonry consultant for the project, and Masonry Building Corp. of Virginia Beach, Va., which constructed the new brick foundation after the move. As on three previous lighthouse-relocation projects, ICC teamed up with Expert House Movers, experienced relocation specialists.
The lighthouse rested on a solid granite foundation, extending 6 feet below grade and resting on a pine timber mat of crisscrossed planking, 6 inches thick, laid on naturally compacted sand. The successful performance of this foundation depended on its continued immersion in the fresh water table, which is high-3 to 4 feet below ground surface. Exposure to air or salt water would have caused the pine mat to become vulnerable to rot or marine organisms. The sand below was very strong because it stayed wet and became extremely compacted over time. The wood, in turn, was able to safely carry the weight of the lighthouse without crushing.
Due to its low center of gravity, the 4,800-ton structure was a good candidate for relocation. ICC decided that the below-grade portion of the granite would be replaced with brick at the new location and the soft octagonal pine mat would be replaced with a heavily reinforced concrete pad.
In January 1999, Wiss, Janney, Elstner Associates tested the materials, performed distress analyses, and installed monitoring equipment. The historic mortar was found to be equivalent to a present-day Type S portland cement-lime-sand mortar. In addition, WJE tested in compression cut brick prisms from the lighthouse shaft and vertical and horizontal cores from the granite plinth, and inspected for pre-existing damage. The 130-year-old lighthouse inevitably had some cracks, but none were of structural concern.
WJE designed and installed a sophisticated computer system in the lighthouse, connected to a multitude of sensors for monitoring stresses, verticality, deformation, vibration, changes in the width of cracks, and other areas of potential distress. "The main thing was to make sure the lighthouse remained vertical," says Jerry Stockbridge, WJE's affiliated consultant. "During the course of the move, it could never be more than ½ of 1 degree out of vertical." This limit had a sizable built-in safety factor; the lighthouse could be out of vertical by 5 degrees before one side would have significantly higher stresses than the other.
A road was cleared, graded, and constructed with a compact aggregate base and movable steel mat and rails.
In spring of 1999, workers began forming and pouring the 4-foot-thick, 60x60-foot concrete pad, which would be heavily reinforced with epoxy-coated rebar, with #10 laid at the top and bottom.
From February through April 1999, the excavation and shoring of the lighthouse took place. Workers dewatered the site, separated the lighthouse from the foundation, and installed a steel shoring-tower system. They then grouped and crossbraced the shoring towers to provide a rigid frame.
Expert House Movers constructed the main support frame between the towers. A Unified Jacking Machine transferred the load gradually from the temporary shoring towers to the main support frame.
On June 17, push jacks propelled the lighthouse 4 inches, beginning the historic 23-day move. The lighthouse moved an average of 130 feet a day, varying from 10 feet to 355 feet. The push jacks drove the lighthouse forward at a rate of about 1 foot per minute.
On July 9, the lighthouse was pushed the final 79 feet of its 2,900-foot journey. The load transfer process was then reversed. While the lighthouse rested upon steel shoring towers, the masonry contractor began laying the clay brick foundation, made up of 140,000 solid low-absorption paver-type units laid in a Type S portland cement-lime mortar. While the spine and ribs were being laid, the masonry contractor built prisms. Fortunately, all of the ribs (and most of the infill between the ribs) were in place when Hurricane Dennis hit the Outer Banks at the end of August. Brick masonry turned out to be the best support as well as the most efficient and economical system to use in this application.
Turned off during the move, the lighthouse lantern shone again on November 13, 1999. Though its importance as a navigational aid has declined over the years, the Cape Hatteras Lighthouse stands as a proud monument to what a talented team can accomplish--with painstaking preparation, constant monitoring, and enormous patience. This article also tells of the effect of Hurricane Dennis on this project.