Building construction pit is an engineering feat

While Superstorm Sandy roared across the District two weeks ago, Cory Surber’s eyes remained glued to his computer screen. One detectable movement, he knew, could be catastrophic.

Surber, a senior project manager with Clark Construction Group, received frequent updates regarding the Science and Engineering Hall work zone – an 85-foot pit covering almost an entire block of Foggy Bottom with a towering crane overhead.

The construction pit for the $275 million building – the most expensive in GW history – emerged from the storm relatively unscathed. But the site poses unique challenges, and supervising the work is a 24-7 job for Surber and his coworkers.

It is just a few hundred yards away from Munson, JBKO and Fulbright halls, with a Blue and Orange Line Metro tunnel running adjacent to the zone. Crews also must deal with weather- or pressure-related shifts between layers of rock and dirt below ground – a concern amplified by the fragility of the site’s surroundings.

“Normally on a downtown D.C. job, there is one building in proximity to the site. This one has three buildings,” Surber said. “It’s an extremely difficult job.”

University President Steven Knapp has praised the work of GW’s longtime construction partner.

“They have had to come up with solutions that are very ingenious. They’ve had to invent new technology,” Knapp said about the Clark project managers.

“Teams from all around the country visit the site because they’re so inspired by the technology,” Knapp added.

The trick is technologically advanced equipment that the company has designed specifically for GW’s project.

Steel shafts and concrete walls surround the rock and dirt near residence halls and the Metro tunnel, creating the same pressure that existed in the ground before the mammoth ditch was dug.

Electronic monitoring systems track any shifts in the ground that could damage the surrounding residence halls. Managers received email updates “every hour on the hour” from the system during Sandy – the first major storm since the hole was dug last October.

Crews used geotechnology, or ground scanning, before excavation to plan out steps needed for the project, slated to be completed in 2014. The teams also used archeological scanning and sound waves to evaluate the thickness of each rock and soil layer to judge the ground’s depth, which can vary drastically in the Foggy Bottom area due to the ground’s density.

With a substantial hole bored into the ground, Surber said the team had to balance the weight of the three residence halls and apply equal pressure on the Metro tunnel that the ground was able to provide prior to being dug up.

Alicia Knight, senior associate vice president of operations, said GW picked Clark because the firm was most familiar with this type of project. Clark proved it could blast near residence halls when it completed the The Avenue last year with similarly complex surroundings.

“There was a whole lot of conversation and planning from the very beginning about how we were going to successfully deliver the project,” Knight said.

The company also had to coordinate with the Washington Metropolitan Area Transportation Authority, which allows blasting only during a set time window and requires that crews to use seismographic instruments to track any pressure shifts that could collapse the tunnel.

WMATA spokeswoman Caroline Lukas said the Metro is used to large scale projects near the subway lines, like when the Verizon Center was built nearly on top of the Yellow and Green Lines.

Pedro Silva, a civil and environmental engineering professor, said he has paid attention to Clark’s work throughout the excavation, adding that it was very difficult to pull off since any even a relatively small force could hurt any of the halls or the tunnel.

“Typically you don’t find that in the field, but I think they did a fantastic job,” Silva said.

Matthew Kwiecinski contributed to this report

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