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Officials investigating why a Silver Line parking garage is sinking

Construction workers install more piles to stabilize the parking garage at the Innovation Center Metro station in Herndon, Va., on Sept. 27. The additional piles are being used to stabilize the parking garage because of signs that the structure sinking. (Cal Cary/For The Washington Post)

A parking garage being built as part of phase 2 of the Silver Line is sinking, and all work on the project has been stopped while an outside engineering firm tries to determine the cause.

Fairfax County officials said the problem at the Innovation Center Metro station in Herndon first surfaced in July when the contractor told them that four of the 135 caissons being installed to support the eight -story garage had sunk — two by approximately four inches.

Caissons are cylindrical structures installed below ground to help support the weight of a structure. Officials say technical consultants have done detailed inspections of the site and are “very confident” there is no risk it will collapse. In addition, an electric monitoring system has been installed to detect any movement of the foundation.

The garage is one of five being built at stations along the second phase of the Silver Line, which will extend Metro to Dulles International Airport and into eastern Loudoun County. But this garage is of particular significance because it is the Metro station closest to one of the sites Virginia is offering as a potential home for Amazon’s second headquarters.

(Jeffrey P. Bezos, founder and chief executive of Amazon, also owns The Washington Post.)

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Carey F. Needham, director of building and design for the Fairfax County Department of Public Works and Environmental Services, said the garage was about 65 percent complete when the problem was discovered. It is not clear when work will resume.

Brian Killion, vice president of operations for the contractor, Manhattan Construction, which has a $33.1 million contract with the county to build the garage, said the company is focused on determining what caused the garage to sink and ensuring the site is stabilized.

“We want to make sure we are delivering a safe and stable project, and we believe we are on track to do that,” he said.

The garage issue is the latest of several problems that have plagued the second phase of the Silver Line project since construction began in 2014.

Earlier this year, project officials discovered problems with more than 1,000 concrete panels installed at five stations. The defective panels are now at the center of a whistleblower lawsuit that alleges workers at the plant that manufactured them deliberately lied on reports about the quality of the work. In August, an employee of the firm that made the panels pleaded guilty to falsifying concrete-quality tests.

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While the Metropolitan Washington Airports Authority is constructing the Silver Line, it will be operated and managed by Metro once completed. Metro’s Office of the Inspector General has launched its own investigation of the concrete problems.

In July 2015, work on the project was halted after officials found cracks in the girders that support the Silver Line tracks at Dulles Airport. Earlier that year, project officials had announced a 13-month delay because of design changes, some related to new state and federal rules tied to storm-water management.

The garage projects are being managed separately from the rail project and are being built by different contractors. As part of an effort to cut the project’s costs, officials in Fairfax and Loudoun counties agreed to take responsibility for building the garages.

The garage at Innovation Center is part of a larger retail and residential development being built on the south side of the station near Sunrise Valley Drive. The Metro station itself will sit in the median of the Dulles Toll Road. When completed, it is expected to accommodate 2,100 cars and have space to park 100 bicycles. Mixed-use development is also being built on the north side of the station.

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Needham said the settling involved caissons located near the center of the garage and affected two supports in different areas. As precaution, grout has been injected into the caissons to stabilize them, he said. The goal is to create a “redundant foundation” and prevent further impacts to the project, said Matthew Kaiser, a county spokesman.

The second phase of the Silver Line will include six stations, including one at Dulles Airport. It is expected to open for passenger service in early 2020. The first phase of the rail line, which includes five stations, opened in July 2014.

The parking garage was slated to open the year before passenger service, so there is time for the contractor to complete whatever repair work is needed, Needham said.

Fairfax Board of Supervisors Chair Sharon Bulova (D) agreed that the garage problems should not interfere with the project timetable.

“Any project the size of the Silver Line will have some issues that will crop up,” she said.