Since its inception in 2006, the most visible aspect of the Panama Canal’s $5.2-billion Third Lane Expansion project has been the excavation of the 6.7-kilometer-long Pacific Access Channel. With the completion of a $42.3-million, 1.8-km-long cofferdam this spring, that excavation is continuing as planned.

The backfilled cellular cofferdam will hold back Miraflores Lake, the man-made body of water between the Miraflores locks and Pedro Miguel locks. Once the cofferdam is finished, excavation of 26 million cubic meters of material in the access-channel route can proceed as well as the construction of a permanent, $70-million, clay-core, basalt-rock-filled dam.

The Pacific Access Channel is a key component of the massive Third Lane Expansion project, slated for completion in 2014. The project will double the historic 80-km waterway’s cargo capacity and allow passage of massive post-Panamax ships.

The larger ships require the construction of massive new locks on both sides of the isthmus. In 2009, Grupo Unidos por el Canal, a consortium led by Spanish contractor Sacyr Vallehermoso SA, won the $3.1-billion contract to design and build the new locks.

For the Pacific entrance, a 6.7-km-long access channel is needed to connect the new locks to the canal’s main navigation channel near the entrance to the Gaillard Cut. This effort, started in 2006, requires the removal of almost 47 million cu m of material, as well as extensive supplementary works.

In December 2009, the contract for the final phase of work on the Pacific Access Channel, dubbed PAC 4, was awarded to an international consortium comprising Spain’s Fomento de Construcciones y Contratas, S.A. (FCC), Mexico’s Empresas ICA and Costa Rica’s Constructora MECO. The group’s $268-million bid bested three other competitors.

The consortium subcontracted the cofferdam work to a joint venture of Richard Goettle Inc., Cincinnati, and Ingenieria Continental, S.A. (ICONSA), Panama. The cofferdam is 1,336 m long; an additional 462 m consists of a sheet-pile cut-off wall. The 15,000 tons of sheet piling—supplied by LB Foster Inc., Pittsburgh—were purchased in advance by the Panama Canal Authority. Twenty-four of the cells measure 21.64 m in diameter, and 34 are 17.83 m in diameter.

Each of the 58 cells is built using a large circular template, surrounded by the sheet piling and welded. Crews dredge silt inside the cells and place underwater tremie concrete where necessary. Then, cells are filled with granular backfill. The entire cofferdam requires a total of 250,000 cu m of aggregate.

To keep the project on schedule, the consortium is using three marine and two land crews; a sixth crew has completed the sheet piling. ICONSA engineer Javier Ferrier, the project director, says the logistics of the effort were by far the most difficult challenge. “We have to meet the demands of the tight schedule and handle coordination with all the agencies,” he says. “At the same time, we can’t interrupt the production cycle of our crews.”

If the cofferdam is completed on schedule, ACP engineers aim to begin work on the Borinquen Dam this fall. That effort is slated to conclude in March 2013.

Currently, ships passing through the canal’s Pacific locks must transit the 1.7-km Miraflores Lake. Passing through the Pedro Miquel locks, the new access channel will be lifted 9.5 m higher than the lake. The dam will separate the two.

The clay-core, basalt-rock-filled dam will be approximately 180 m wide at its base and 30 m at its crest. It will require 5 million cu m of material to fill; more than three-fourths of the fill will be supplied from the dry excavation included in the contract.