Jet grouting at a New York landmark

Keller will soon finish jet grouting on one of the most famous structures in the world: the Brooklyn Bridge. Working in confined, low-headroom spaces, the team has overcome numerous challenges – including a nine-month shutdown due to a strange discovery…??

A cultural and architectural icon, the Brooklyn Bridge has spanned New York’s East River between the boroughs of Brooklyn and Manhattan for almost 140 years.??

Over the decades, the landmark has undergone several periods of restoration to maintain the bridge’s appearance and keep it safe for the millions of people who cross it every year.??

In 2019, construction companies Navillus and MLJ were awarded a contract worth more than $300 million to maintain and repoint the bridge’s two familiar towers and replace walls and facades on the arches that support the approach roads from either side of the bridge.??

Refining the scope??

Historically, these arches have housed restaurants, shops and even a wine cellar, but they’ve now lain empty for many decades. It’s in the basement of four of the arches on the Manhattan side that Keller is underpinning the foundations by constructing some 2,600 jet grout columns.??

"Our reputation, size, expertise and the fact that we can work in a such a limited access environment, all helped us secure this prestigious contract,” explains James Myers, Keller Senior Project Manager.?

“The initial scope was very prescriptive, but we were able to make improvements, changing the sequencing slightly to save the client time and money. We also created more space between the overlapping columns and recommended a slightly larger column diameter – 6ft instead of 5ft – in some instances. This helped create a better product and production rate.”

Unearthing the past?

The bulk of the work took place in archway blocks C and D, each around 20ft wide and 85ft long, with just 9ft of headroom. “Having three limited-access rigs readily available is something a lot of competitors would have difficulty with,” says James. “At Keller, we design and build our own. Once these were secured, we spent a lot of time planning and ensuring we could move the rigs and crews around within the confined space.”?

Another challenge was removing the large quantities of spoil produced. A vacuum was used to suck the spoil into collection pits, a process that needed careful monitoring. If spoils aren’t continually returned, there’s a risk of over-pressurising the soil, resulting in damage to the structure.

However, the biggest setback during the project came right at the start and from an unexpected source: cow horns.?

“We mobilised and started in May 2020, just as everything was shutting down due to the pandemic,” says James. “The streets of New York were empty, and it was all very eerie. We set up, and then during our initial tests, we found some cow horns. This set off an archaeological inspection, which quickly uncovered a hundred more.??

Further investigation was required and what was originally scheduled to take a few weeks soon turned into several months. The bridge is built on old swamp ground, with tanneries and slaughterhouses once common in the area. The experts concluded that the horns were dumped there as waste and the finding was not significant.??

Full steam ahead?

James says that having equipment sit idle and crews unsure when they’d be ready to start was a headache, but Keller is big enough and agile enough to handle such a disruption. The horns were disposed of, and the team finally got back on site in February 2021 with test columns, and full production began at the end of April. A second crew was added in June and a third in August.??

The unexpected discovery of significant amounts of peat during testing resulted in the team having to react quickly to change the mix, and more recently, a cement shortage added further challenges. The project’s now on schedule to finish in April 2022.??

“With a job of this nature, there’s always going to be a lot of pressure – no one wants to be responsible for damaging the Brooklyn Bridge!” says James. “But with that also comes a lot of pride that we’re working on such an iconic structure. We’ve overcome many challenges, but we have a good production rate, the quality is excellent, no movement has been attributable to us, and we have a great relationship with the client. We’re looking forward to successfully completing our work on this iconic landmark.”??