A highway contract involving one of the U.K.'s largest-ever box jacking operations ended successfully ahead of schedule and under budget seven years ago, going on to win an innovation award from the Institution of Civil Engineers.

But then problems began to emerge with the project, which led earlier this month to the design firm facing a bill of around $2 million.

Atkins, the U.K.-based infrastructure unit of SNC Lavalin Group, was ordered earlier this month by the U.K. Technology and Construction Court to compensate the design/build contractor on the East Kent Access Road Phase 2 project for remedial work on the highway and legal costs for its deficient work on its subcontract, starting some 10 years ago.

Atkins had failed to convince the judge at an earlier hearing this July that the fault lay with contractor, and now must make the payment before Christmas.

East Kent Access Road Phase 2 project covered 8 km of construction to improve two highways. It included a 126-m-long tunnel under a railroad and also a two-span bridge further along the tracks at Cottington Road.

A joint venture of Hochtief (U.K.) Construction Ltd. and Volker Fitzpatrick Ltd. won a design-build contract from Kent County Council, valued by Volker at $110 million, in August 2009. The team subcontracted WS Atkins Ltd., then an independent stock exchange listed company, for detailed design.

To build the tunnel without disrupting rail traffic, the joint venture embarked on a major jacking operation. From an excavation next to the tracks, the contractor used hydraulic jacks exerting up 36 tonnes force to push six 2,500 tonnes consecutive box sections under the railroad while excavating the ground ahead. The tunnel was completed in spring 2012, while work had ended on the bridge in the previous year.

After the bridge was completed in 2011, localized depressions appeared in the highway on both of its approaches, according to the court. Remediation work by the joint venture went on between 2012 and 2014.

Ruling the design to be "inadequate, negligent and in breach of the subcontract" in a hearing this July, the judge found Atkins liable to pay the contractor over $1 million compensation. The record-breaking tunnel also exhibited faults, including leaks, rust staining and fine concrete cracking.

The contractor incurred substantial costs fixing this problem, claiming $160,000 compensation from Atkins. But in that case, the judge ruled in the design firm's favor.

This month, the court settled additional claims for interest on the original compensation and Atkins' share of the joint venture's legal costs, raising the total to around $2 million.

While Atkins, which declines to comment, is left out of pocket, the contractors claim that their original work was faster than expected and more than $3 million under budget.