This fall marks the 400-year anniversary of the famed Mayflower landing—in what is now the Commonwealth of Massachusetts—the site of the first permanent European colony in New England. Before the vessel landed at what is now Plymouth, it stopped in a sheltered harbor, now known as Provincetown Harbor, at the tip of Cape Cod. It was here that the Pilgrims signed the Mayflower Compact, the first governing document of their new colony.
Almost 300 years later, in 1910, a monument that is still the tallest freestanding granite tower in the United States was built to commemorate the Pilgrims’ landing at Provincetown. And it is also here that an inclined elevator is being built to improve access to the monument and honor the area’s centuries-old history.
The elevator will be located on the side of a steep hill, known as High Pole Hill, offering a pedestrian connection between Provincetown’s commercial downtown and the almost 253 ft tall Pilgrim Monument at the top. The cornerstone of the monument was laid by President Theodore Roosevelt in 1907, and the completed structure was dedicated by President William Howard Taft in 1910.
The inclined elevator will transport up to 18 passengers at a time. The cabin will operate on a track between two 20 by 20 ft pavilions, one located within the town’s Bas Relief Park, which commemorates the signing of the Mayflower Compact, and the other about 80 ft higher at the top of the hill.
Like most of Cape Cod, the hill comprises loose sand. “The outer Cape surficial geology is essentially a giant sand dune formed from the post-glacial deposition of sand and silt from the last advance and retreat of [an] ice sheet,” says John Bologna, P.E., M.ASCE, the president and chief executive officer of Coastal Engineering Company Inc., of Massachusetts. He is the engineer of record for the civil and structural design of the project. “Slope stability and the integrity of the rail support structure were predicated on the use of deep helical-pier foundations,” Bologna says. These foundations were necessary to minimize ground movement during construction and the operation of the inclined elevator.
“Slope stability and the integrity of the rail support structure were predicated on the use of deep helical-pier foundations.” — John Bologna, P.E., M.ASCE
The elevator will use a single tram that will operate at 200 ft/minute, taking approximately two minutes to make a one-way trip between the pavilions, according to Bologna. The mechanism and hoist for the elevator will be placed at the top of the hill. It is anticipated that the system will run throughout the day during the summer season, with shorter operating hours during the off-season.
The helical piles that will support the upper platform’s foundation comprise a lead section with three helix-bearing plates attached to straight, roughly 2.9 in. diameter extension pieces that create the necessary pile lengths. The helical piles will reinforce the loose sand and increase the site’s overall stability. “I think the big surprise in the project was the pile load-test results, which indicated that the helical piles had to be deeper than anticipated,” says Larry Dwyer, P.E., M.ASCE, a lead geotechnical engineer on the project for GM2 Associates Inc., which has multiple offices in New England. Rather than 20 ft, the piles had to extend 45 ft deep to reach their full compression and uplift capacity.
The piers, upper pavilion, and rail foundations were designed so that the hoist mechanism would pull the elevator up the hill without affecting the stability of the nearby monument or the Provincetown Museum, which is also located on the hill. “There are four [helical piles] that will [be installed] at an angle, serving as tiebacks for the tension load from the mechanism itself,” Bologna says. “And then down the rails approximately every twelve feet on center there is a pair of helicals that act as the frames to hold up the rails in between.”
Because of Provincetown’s location at the tip of Cape Cod, which juts approximately 70 mi into the Atlantic Ocean, the project had to be designed for high winds, snow, and thunderstorms. “Cape Cod … usually bears the brunt of major storms coming up the New England coast,” Bologna says. “The site locus is in a designated hurricane-prone area and subject to one hundred thirty-eight miles per hour, three-second gusts of wind.”
The lower pavilion is in a flood zone, and the elevator pit that will house some of the system’s mechanisms is below grade. So the elevator pit had to be designed for both high-ground water levels and hydrostatic flood forces on the structure. A sheet pile cofferdam enclosure was built, dewatered, and then fitted with a precast concrete box that was also anchored with helical piles to form the lower section of the elevator pit, Bologna says.
The inclined elevator was originally slated to be completed this year. However, because of COVID-19-related delays, it is expected to open in 2021.
This article first appeared in the September 2020 issue of Civil Engineering.
