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Keller completes Capitol Crossing foundations

Keller companies Case Foundation and Bencor have completed the foundations for a development that will span the I-395 highway in Washington, US.

The 204M.m² Capitol Crossing development will span a sunken part of six-lane I-395 highway, with the initial designs to build a platform supported on 149 drilled shafts using 10 different pile sizes ranging from 1m to 3.6m in diameter.

Keller said: “We worked with the design team and made recommendations to reduce the number of shafts required. We carried out rigorous load tests installed with the support of our McKinney Drilling colleagues several months prior, giving the project team confidence in streamlining the design.

“This resulted in a reduction of the number of different diameter sizes to four (ranging from 90cms 3 to 2.4m), leading to a 6.5% reduction in project foundation costs and 10% reduction in the foundation construction schedule.”

According to Keller, the plan involved the team installing the drilled shafts in four phases, with two drill crews carefully coordinated to minimise disruption. Work within the highway median proved to be one of the most challenging aspects due to a working area barely 9.75m wide – just enough room for the BG-39 rig and 200t crane to pass each other, the firm said. 

The piles were installed up to 39.6m deep through sands and lean clays using a combination of polymer slurry and vibratory casing.

Case teamed up with sister company Bencor to construct the slurry (diaphragm) wall.

The Case and Bencor team improved the proposed design and reduced the schedule and costs by eliminating the need for different panel widths and slashing the overall area by 5,000 ft2, according to Keller.

The new design featured 36 panels each 91.4cms wide and installed between 18.6m and 23.2m deep with a total area measuring just under 464.5m².

Moretrench then provided a primary dewatering system of 33 deep wells for the underground car park, using a mud rotary drilling method.

The construction of Capitol Crossing is on schedule to be completed by 2021.

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