当码头的第一阶段于2017年10月开放时，大规模的综合用途开发立即为华盛顿特区西南滨水区提供了将近200万平方英尺的增加。它立即交付，创造了一个新社区的基础，其中包围着广泛的建筑物，这些建筑物被公共场所包围着，可以进入华盛顿频道。For developer Hoffman & Associates (H&A) and its design and construction partners, the project also provided valuable insight into how it would approach the development’s 1.2-million-sq-ft Phase 2. “We learned a lot, and our team did a great job of keeping track of lessons learned—from major change orders to soil conditions,” says Maria Thompson, executive vice president of development and construction at H&A. “We ended up with a 25-page Excel spreadsheet that we used extensively in the planning and design of Phase 2.”

The support of the excavation wall consisted of tangent piles installed by displacement drilling. The wall was braced by preloaded rakers with heel blocks integrated with the permanent building footings.
Photo courtesy of Hoffman & Associates

Early Efforts

Early planning of the 3.2-million-sq-ft, $3.6-billion development began in 2006. After years spent gaining site control from the District of Columbia under a long-term ground lease, a master plan, created by Perkins Eastman, was in the works by 2010. That plan called for breaking the site—which spans nearly a half-mile of waterfront—into 10 parcels with large underground parking garages serving as podiums for new buildings.

Shawn Seaman, H&A’s president, says the team wanted to replace the existing “superblocks” on the site—some of which were as long as 1,200 ft—with a series of smaller buildings intersected by public access points. “What really needed to happen to transform the site was to look at a smaller grain development,” he says. “Our blocks are 250 feet long at most, which has a lot of permeability to allow pedestrians access through the site out to the water. Putting the parking below grade was the fundamental change that allowed us to come up with that plan.”

Targeting a 2014 construction start, Seaman says H&A had financing in place, a fixed budget and a fixed schedule, all of which drove the decision to sign a nearly $600-million design-build contract with Clark Construction. “At that point,” he says, “we were running short on time to start the project with the District and we were really intent on maintaining cost, maintaining schedule and getting the project delivered in the three-and-a-half years that we had allocated.”

Located on D.C.’s Southwest Waterfront, The Wharf includes a historic fish market, hotels, residential units, restaurants, shops, parks, piers, docks, marinas and live music venues.
Rendering courtesy of Hoffman-Madison Waterfront

第二幕

For Phase 2, which broke ground in 2019, Seaman says H&A preferred to use a more traditional design-bid-build delivery, contracting directly with multiple architects and contractors. While Perkins Eastman remained as the master planner of the Phase 2 garages, H&A tapped a new set of design and construction firms to offer a fresh perspective on other elements. The team of SHoP Architects and WDG Architecture with Balfour Beatty Construction are delivering a 500,000-sq-ft, two-tower, trophy-class office building.

Donohoe Construction is building a 380,000-sq-ft facility, designed by ODA Architects, which features 255 apartments and a 131-room hotel. Donohoe is also building the 240,000-sq-ft Amaris luxury condominium building, designed by Rafael Viñoly Architects. Last year, DPR Construction completed work on a 90,000-sq-ft trophy office building designed by Morris Adjmi as well as two retail buildings on the pier.

“It’s a nice assemblage of architects with a little bit of a different approach than Phase 1,” Seaman adds. “Visually, it’s different than Phase 1, which is a positive.”

Although each building in Phase 2 provides a unique look, Douglas Campbell, associate principal and managing director at Perkins Eastman, says the development retains the appearance of a cohesive neighborhood. The “big idea” of the master plan, he says, was to deliver a development that looks like it was created over a number of years, rather than in large phases. “If you look at each piece individually, Phase 2 makes some bolder statements [than Phase 1], but it all holds together,” he says.

地下

With those bold statements come more complex structures, Campbell says. Design of the parking garage, which serves as the podium of the building, also faced significant structural challenges. To help streamline the structures, a joint venture of SK&A and Thornton Tomasetti serves as structural engineer for the various projects. “We needed the same structural team working from the head to the feet because this all had to work together,” he says.

In addition to driving piles around two Metro tunnels, the project team also built an underground parking garage next to the tunnels.
Drawing courtesy of Thornton Tomasetti
*Click on the image for greater detail

Before work on the main structures could get underway, H&A addressed the seawall. Thompson says the Phase 1 seawall was delivered in sections, as teams excavated portions then built new concrete walls in sequence. For Phase 2, the team decided to use an 800-linear-ft king pile system. The team installed the entire new seawall 24 in. from the existing seawall to depths of up to 85 ft into the channel. Once that work was complete, crews could demo the entire existing seawall. Thompson says the seawall, which was designed by Moffatt & Nichol and built by Cianbro, was completed two months faster than it would have been under the Phase 1 method, according to Thompson.

Installing a deep king pile system also enabled designers to add a third level to parts of the parking garage. Campbell says that strategy allowed the team to maximize available parking spaces, while also accommodating the placement of building utilities in the parking garages. With a deeper parking garage, the site was also excavated down to firmer soils, says Mark Tamaro, managing principal at Thornton Tomasetti. He says the soils near the Washington Channel contain silty alluvial material, especially close to the ground level. For the two-level parking garage, crews installed approximately 2,800 rigid inclusions at depths of 20 to 30 ft to help strengthen the soils. “That allowed us to use a higher bearing pressure but allowed us to implement spread footings—an economical approach,” he adds.

但是，对于三层车库，可以使用宽的基础，而无需进行地面改进。塔玛罗补充说：“他们把车库带到了一个更好的轴承层……具有切入的好处，您获得了更简单的基础系统。”

尽管停车场设计使团队能够更好地实现其更大的码头愿景，但该策略面临着重大挑战。除了车库与华盛顿通道的距离外，108英寸DC水管还可以分叉公寓楼和Amaris公寓之间的地点。从结构上讲，设计师决定在管道位置拆分停车场。在整个施工过程中，管道一直保持原状，受到监测和保护。安装了喷气式灌浆柱，以确保管道保持隔离和保护。

在达到35英尺深度的发掘过程中，采用了各种各样的支撑系统。除了国王桩系统外，船员还安装了约1,400英尺的板桩墙，157个钻孔士兵桩，打plack，拉杆，横杆，越过的叉括号，由尖顶和带有高跟鞋的射手预装，包括一些如此之大，以至于将它们结合在一起，带有基础或起重机基础。

The project team erected a seawall and 12-story Viñoly Tower with sloped columns directly above the Metro tunnels.
Photo courtesy of Hoffman & Associates

桩推

Perhaps the project’s most challenging aspect, however, was the alignment of two decades-old Washington Metropolitan Area Transit Authority (WMATA) tunnels that curve through the site, directly below the Amaris project. The tunnels themselves are constructed of steel liner plate, rather than concrete, which is more prevalent in the Metrorail underground sections, which needed to be protected, says David Good, principal at Mueser Rutledge Consulting Engineers. The steel liner plate “is thinner than cast iron or reinforced concrete and therefore requires additional protections,” Good says.

To address concerns, a 5-ft construction exclusion zone was created around each tunnel. However, Good says the tunnels were held in place by the soil loads, so any change in those loads threatened to move or damage the steel tunnels. Because the parking garage and the Amaris are located above the tunnels, soils had to be excavated from above the tunnel alignment at depths of roughly 14 ft, and could differentially relax the load on those tunnels.

Mueser Rutledge and Thornton Tomasetti devised a system that would preserve the tunnels and maintain loads within a threshold of 300 pounds per sq ft. Above the tunnels, crews installed a 4-ft-thick mat slab foundation. Traditional drilled piles couldn’t be used because any removal of soil would cause differential relaxation, Good says. Instead, a support of excavation wall was built using 443 drilled displacement piles and 18-in.-dia continuous flight auger piles in tangent configuration within 10 ft of the tunnel structure.

“We essentially pushed piles into the ground,” he says. “So instead of the tunnels moving toward the excavation—which is traditional—they actually moved away because of the force of those DDP piles. Then when we did the excavation it would come back a little bit.”

Installation of these elements required constant tuning of loads, as drilling piles in proximity to the tunnels could cause beyond-threshold load changes. “The creative solution that the Mueser Rutledge team came up with was a series of [16] dewatering wells, where they could adjust the water level around the tunnels,” Tamaro says. “As you lower the water table, you’re actually increasing the overburden above because instead of being material that’s buoyant, it’s now become heavier.”

Workers pour concrete for the sloped columns on the third level of the Viñoly Tower.
Photo courtesy of Hoffman & Associates

难度程度

In addition, the structural design of the Amaris tower placed a stair core directly above the tunnel alignment with no transfers within the tower itself. The team designed a system of load-sharing elements. It installed in this parcel 132 grouted hollow bars with diameters of 8 in. to 12 in., at depths between 60 ft and 90 ft. By using hollow bars, the system could be installed beside and even between tunnels, functioning in both compression for load sharing and tension for uplift resistance.

在隧道附近的结构如此之多，人们担心从公寓大楼中感觉到WMATA Metrorail火车的振动潜力。H＆A致力于花费1200万美元用于缓解振动，在WMATA隧道附近的所有基金会下方和旁边安装专门的振动隔离材料。该公司的创始人兼董事长蒙蒂·霍夫曼（Monty Hoffman）说：“我们无法做到这一切，归根结底，居民觉得上午7点的火车通行证在他们的下方。”“在这种情况下，我们谨慎行事做正确的事。”

Above the tunnels, the Amaris is one of The Wharf’s signature buildings, serving as a virtual gateway from the eastern end of the development. The building features an orthogonal design at the elevation that meets the rest of the development and an expansive curved facade that faces into an open park on the opposite side. “The idea of the tower was to pull it back from the public park and effectively our tower becomes the face for the whole development,” says Jay Bargmann, vice president at Rafael Viñoly Architects. “Then you have views of the marina and downtown D.C. that follow the curving sightlines.”

At either end of the curved facade, the building slopes out at approximately 28 degrees. At the eighth floor, the structure transitions from vertical and sloping to just sloping. The sloped columns resolve back at a thicker non-post-tensioned slab at Level 3.

为了创建建筑物戏剧性的弯曲元素，设计团队指定了冷栅玻璃面板。该技术允许面板平放，然后在安装过程中，可以通过弯曲系统将角延伸到位。

“这可能是一个更令人生畏的elements of the design for the owner to take on, but we talked them through the technology,” recalls Jac Selinsky, project manager at Rafael Viñoly Architects. “During construction it was actually one of the smoothest constructed components of the building. Those curtain walls went up in about eight weeks or so with no hiccups or delays. It all went up like clockwork.”

汤普森（Thompson）估计，冷蜡玻璃组件提前一个月完成。

根据开发商的说法，第2阶段的主要包裹将按计划今年交付，从3月的办公楼开始，并于11月与Amaris结束。

“We learned a lot in Phase 1,” recalls Hoffman. “It was all a bit of an experiment, but we were really able to dial it in on this one.”