A construction team led by Spanish contractor Sacyr Vallehermoso SA has won the mammoth Panama Canal expansion’s largest contract to date: the design-build job to build a third set of locks on the waterway’s Atlantic and Pacific openings.

The locks contract is the heart of the $5.2-billion effort begun in September 2007 to expand the historic waterway. The winning team, which includes two U.S. engineering firms, proposes to construct the locks for $3.12 billion. The job had been estimated by owner Panama Canal Authority (ACP) to cost $3.48 billion, the quasi-government agency revealed on July 8.

The winning team, known as Grupo Unidos por el Canal, also includes three other contractors: Impregilo SpA of Italy, Belgium’s Jan De Nui NV and Constructora Urbana SA (CUSA) of Panama. Constructora Urbana is already working at the site on other canal-related projects.

Also on the team are two U.S. firms—Broomfield, Colo.-based MWH and Tetra Tech, Pasadena, Calif.—along with Holland’s IV Groep. Heerema Fabrication Group, also based in the Netherlands, is a team member as well.

The selection was based on Grupo Unidos’ total score, including technical evaluation and price proposal, ACP officials said. Technical proposals were evaluated based on execution of construction and operations, design of electronic and mechanical systems and design of the locks’ structures, gates and hydraulics, the officials explained. More than 50 technical experts who participated in proposal review signed confidentiality and conflict-of-interest agreements, according to ACP.

The selection is the culmination of a process that drew into the competition four teams comprising 30 global firms. One team chose not to submit a proposal, but the other two whose proposals fell short in the final competition were led by Bechtel International Inc., San Francisco, which offered $4.2 billion for the job, and Spain’s ACS Servicios, Comunicaciones y Energía, S.L., whose proposal was close to $6 billion, according to ACP. The Bechtel team included Taisei Corp. and Mitsubishi Corp., both of Japan. The ACS team included Germany’s Hochtief Construction AG and Constructoras ICA SA de CV of Mexico.

ACP initially sought proposals for the locks contract in December 2007, with submittals due the following August. Participating teams requested the agency extend that deadline until March 2009, but ACP officials say the delay will have no effect on the overall timeline of the expansion.

The proposed third set of locks will employ sliding gates similar to those at the Barendregt canal in Amberes, Belgium, and a series of water-saving basins used in Germany. ACP chose to integrate both the Atlantic and Pacific locks into a single design-build contract in order to ensure consistency in the final product.

The single-lane, three-step set of locks will consist of lock chambers measuring 427 m long x 55 m wide x 18.3 m deep. When complete, it will allow larger post-Panamax ships to use the waterway. Observers say the team will be challenged in building such mammoth structures and in coordinating the locks construction efforts simultaneously on either side of the Isthmus of Panama.

The expansion is to be completed in 2014, in time for the canal’s centennial, and will more than double the capacity of the historic waterway. “Today’s event marks a critical milestone for ACP and Panama as we determine which consortium will design and build the canal’s new locks,” said agency administrator Alberto Alemán Zubieta. “Throughout the review period, the ACP’s Technical Evaluation Board and external auditors ensured an airtight course of action that reflects our staunch commitment to a fair, rigorous and transparent contracting process.”

ACP has spent nine months organizing project management in conjunction with its program manager, Denver-based CH2M Hill Cos.