Building on Battery Wharf

by Clair D. Urbain

Skanska USA Building Inc. takes on the elements and logistics to build luxury on Boston’s historic waterfront.

With tremendous respect for history, Boston is a vibrant city that keeps one eye on its future while the other eye guards its great past.

Perhaps that’s one of the reasons the Battery Wharf on the city’s North End only recently has undergone revitalization. The wharf is made up of a granite block seawall that dates back to the 1800s and, until recently, proposed a formidable challenge to developers: How can you take advantage of the land and harbor sides of the historic seawall without removing it, damaging it or modifying it?

Most recently, it was a seafood processing plant and retail facility for Bay State Lobster, a Dunkin’ Donuts store and a parking lot. Today, the site is undergoing a $275 million revitalization in the heart of one of Boston’s oldest neighborhoods.

The 807'-long seawall, although not formally listed on any historic register or protected by any formal agency, is being preserved, albeit at considerable design and expense. Even more surprising, the only way the historic seawall may be seen when the project is finished is in a boat at low tide.

Nearly 50 percent complete, the site is a beehive of activity as general contractor, Skanska USA Building Inc., transforms the site into a mixed-use property with retail establishments, luxury hotel and meeting center, high-end condominiums and parking garage. The four-building Battery Wharf complex will rest on both sides of the wharf, with two buildings sitting on piers driven into the harbor with foundations that carry the weight over the seawall. Two other buildings sit on the back side of the seawall. It will appear to be one 485,000 sq. ft. property, says Kerim Evin, senior vice president and operations manager for Skanska’s Boston office. He is also the project executive for this ambitious building project due to open early in 2008.

“This project presents numerous challenges. We’ve had to deal with weather and seasonal tides throughout construction, tight site logistics and unforeseen soil issues that affected our earth support and excavation,” says Evin.

Weather and tide
Just as the 12'-high historic seawall protects the shoreline from the pounding waves brought on by weather and tidal forces, the buildings’ design must allow the wall to remain in place without significant alteration. To accomplish that, the support structures of two of the buildings that will make up the five-star Regent Boston Hotel and luxury condominiums must bridge the seawall without resting on it or modifying it in any significant way.

On the harbor side, pilings were driven up to 110' deep and then precast concrete forms were laid across them to straddle the seawall. They also carry the foundation to the land side of the wall.

“These precast forms were then filled with concrete to complete the foundations of the buildings that extend over the seawall,” explains Evin. “In some of the forms, utilities were located inside them and then encased in concrete. This solved some of the space issues involved with the buildings on the harbor side. The precast wharf was redesigned, which ultimately saved about $.75 million in construction costs,” Evin says.

The steel pilings adjacent to the seawall had to be notched to allow the beams’ precast forms to reach the foundation on the land side.

“These notches lowered the level of protection from high tide and high winds, which could push water over the seawall and into the foundation. We sealed the gaps with hydraulic cement to keep the hole from getting flooded. That really worked well,” he says.

On the land side of the wall, the facility required excavation of up to 45' of soil to make room for the hotel’s meeting rooms, back-of-house functions and parking garage. Water infiltration from the harbor was a great concern.

“We originally proposed eliminating the cast-in-place concrete foundation wall and having the vertical sheet piling serve as a permanent wall and becoming an integral part of the buildings’ foundations. While this is practically unheard of in the United States, it is more common in Europe and would have saved nearly $3 million in construction costs. However, the engineers involved with the project’s design weren’t sold on the concept and elected to install the pilings, then pour a 30"-thick foundation wall as originally designed.

“It would take more than three months to pour the foundation as originally designed, which would have held up the rest of the building,” says Evin.

To overcome that challenge, Skanska proposed extending the steel framework down to the footings so construction could continue above ground while crews came back and used mobile gang forms to pour the foundation below ground. “The foundation is poured right around the steel frame. It becomes a part of the foundation. There was an additional cost to this method, but it took the foundation out of the critical path and allowed building to proceed. It more than paid for itself in cost savings associated with time,” says Evin.

The tidal pressure also caused some tense times. While excavating the area for the southwest corner of the site, one of the sheet pilings failed and flooded the excavation. “We lost three pieces of construction equipment in that flood. Divers located where the failure occurred so we could fix it and then we pumped the hole. That happened on a Friday night, and we were excavating again by Wednesday. It looked catastrophic, but it didn’t affect our schedule as much as we thought it would.”

While beginning construction on the concrete wharf, it appeared that the concrete piles and sheet piles were exhibiting signs of movement. In some cases, they moved 8". It was presumed tidal action was causing this movement, but it was never fully explained by the engineers. “We had to sit tight on fabricating the wharf elements for a short time while they settled down, which they did. Fortunately, the deviation didn’t affect the scheduled placement of the precast concrete forms,” Evin says.

“As excavation continued for the building on the northwest corner of the property, unstable soil conditions and extremely tough pile-driving conditions slowed progress. We ended up having to add braces in the excavation to stabilize the perimeter pilings and install grout curtains to ensure water cutoff. This caused us to completely re-sequence the erection of the buildings,” says Evin.

Jobsite logistics
Due to the delayed excavation on the northwest building, crews gained momentum on the buildings on the harbor side of the project. This created logistics problems throughout the site.

“The street that bisects the site is built over the meeting rooms, parking garage and back-of-house areas, so it couldn’t be used to move equipment until major portions of the foundation and structure were in place. That meant we could only feed equipment and materials onto the site through a 12'-wide access point on the north side of the property. Even then, we had to create reinforcements to support some of the heavy equipment that needed to get back there,” he says.

Although the street bisecting the site can now support truck and other vehicle traffic, the various crafts working on the buildings are requiring supplies and equipment deliveries in a timely fashion. The Boston Police department has a traffic detail on the site to maintain traffic flow around the large trucks delivering goods.

“We even brought in an extra crane to place utility enclosures on the rooftops of the two harbor-side buildings because we didn’t want to take time away from the other crane that’s placing steel for the northwest building,” he says. The work continues like clockwork as windows are installed, mechanicals, electrical and plumbing are roughed in and drywall is hung.

“It’s a bit more complicated because the floor-to-floor height in the buildings is 9'2" but the finished ceiling height is 7'6". That’s not much room to run mechanicals and they must all fit in the ceiling,” he says.

Building material prices have also played havoc with the project, but by working in a design-assist fashion on certain portions of the project, Skanska subcontractors have been able to reduce the impact of the increases.

“We have been hit by two irregular material price hikes, mainly in structural steel, copper and petroleum-based products. By working under a design-assist structure for some parts of the job, it is the only way we could look for savings to offset the rising cost of material,” Evin says.

Published in the July/August 2007 issue of Contractor Tools and Supplies magazine.

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