West Tisbury town hall not razed but raised
The West Tisbury Town Hall is up in the air. Looking a bit ungainly on its temporary wooden stilts, it floats four feet higher than it has been for the last 138 years. The next step in the renovation of the historic building is to construct a new foundation under it and lower it gently down again. The subcontractor for the lifting is Gary Sylvester's Building Movers of Falmouth. The process started last week, and foreman Kevin Winget told The Martha's Vineyard Times that the building will be ready today for its new foundation. A different subcontractor will soon be building concrete forms under the perimeter walls.
Carefully lifting a three-story building that weighs 80 tons may seem like a task for Aladdin's genie, but company owner Gary Sylvester explained that it is not, though it does require care, skill, and expensive lifting equipment.
On the corner closest to the old playground, Mr. Sylvester's crew removed short pieces of the granite foundation and dug under the building. The granite blocks removed were a small percentage of the entire perimeter and therefore not enough to cause the building to shift or sag. Short lengths of heavy timbers in a crib, such as the ones used to dry firewood or shore up tunnels in old-fashioned mining, were stacked under the corner to replace the support of the missing foundation corner.
Photo by Dan Cabot
With the stability of the corner established, small sections of foundation could be removed and similarly supported. When both corners and the foundation on the west side had been removed and cribbed, heavy equipment excavated under the west wall. Using front-end loaders and hydraulic jacks, a massive steel I-beam, also supported by cribs, was placed across the width of the building. That first beam is now approximately under the former work stations of Jennifer Rand and Simone DeSorcy. Eventually three more I-beams, each weighing three tons, were similarly put in place evenly spaced down the length of the building. The cribs under the I-beams are back from the perimeter, to allow the new foundation to be built directly under the walls.
After the four beams across the width were placed and cribbed, three longer I-beams, also supported by cribs, were run the length of the building under the four crossing I-beams. Eight of those cribs contained hydraulic jacks, which lifted the building simultaneously in a process called "unified jacking." The eight heavy-duty jacks and the controls that operate them cost about $50,000, according to Mr. Sylvester. The crew used lasers to check constantly that the building remained level as the centrally controlled jacking system raised it. By reading the pressure on the jacks, Mr. Winget calculated that the empty building weighs about 80 tons.
The crib heights under all the I-beams were raised incrementally as the town hall slowly rose, but the corner cribs, which would be in the way of the foundation work, have been removed. Mr. Sylvester's crew will take the jacking system away this week, leaving the building supported on many cribs. After the foundation has been poured and the concrete sets, they will bring back the jacks to gently lower the venerable town hall onto its new base, perhaps as early as mid-November.