Panama Canal Authority (ACP) committed with the $5.25 billion Expansion Program with the goal of creating a new lane for larger vessels to be able to transit the canal. The Panama Canal Expansion Program includes the deepening and widening of the current navigation channel, the construction of two additional locks -one at the Pacific Ocean and another at the Atlantic Ocean-, and the construction of a new access channel at the Pacific end.
The recently completed Panama Canal Expansion Project required construction of a 6.1km long channel at the Pacific entrance to the Panama Canal, to provide navigation access from the new Post-Panamax three-level locks complex to the Gaillard Cut section of the Canal. This new access channel runs almost parallel to both original locks on the Pacific side and required the excavation of approximately 50 million cubic meters of unclassified material and the construction of four dams, known as Borinquen Dams 1E, 2E, 1W, and 2W. The dams retain Gatun Lake, the main reservoir and waterway of the Panama Canal, approximately 11m above the level of Miraflores Lake and 27m above the Pacific Ocean.
Execution of the Pacific Access Channel sub-program was critical to the Panama Canal Expansion Program and any flaw on its construction process would have a major impact on the Program and on the existing Canal operations. For its construction, the PAC was divided in to four ‘phases’, PAC-1, PAC-2, PAC-3 and PAC-4, the latter being the only one that includes excavation down to the design elevation and construction of Borinquen Dam 1E,
A key consideration for construction was the management of the earthworks under the local climatic conditions and the control of groundwater in the work area. Groundwater levels, which are near the level of Miraflores Lake over a broad area of the Pacific Access Channel, were lowered as much as 20 m to allow construction of the access channel and the dam in the dry. A 1,800-m-long, 20-m-high rockfilled cellular cofferdam was built to retain Miraflores Lake above
the foundation excavation level of Dam 1E. Construction of the cellular cofferdam and the installation of a dewatering system allowed excavation, handling, processing, and stockpiling of finegrained residual soil materials during the 7- to 8-month-long wet season, which is characterized by an average monthly precipitation of nearly 250 mm, in addition, to also allow the placement and compaction of such materials in the dam core. The extensive system of dewatering wells, drainage ditches, detention basins, sumps, and pumps was installed to dewater the access channel area and to control surface runoff from precipitation during construction, while excavations on higher areas were being performed. Also, a 3.5km Diversion Channel built to divert the Cocoli River was critical to achieve dry conditions during the construction of the access channel.
Space constraints associated with navigation requirements within Miraflores Lake were a challenge during construction. The main challenge for performing these works was to have no impact on the canal operations. The alignment of the cofferdam was very close to the Pedro Miguel Locks, and the coordination for the works was very strict to achieve that goal, especially since the works included the dredging of a 335,000 cubic meters from a trench at the bottom of Miraflores Lake to properly embed the cofferdam into the soil by removing unstable material, also several floating-cranes and auxiliary barges were on site once the sheet-pile driving started.
During the entire construction of the cellular cofferdam, there were no construction activities that affected the transit of vessels thanks to the continuous coordination and communication with canal transit and locks operations.
For building the Borinquen Dam Core, the material selected was residual soil. It has to comply with special characteristics to guarantee its function as an impervious water barrier. Compliance with these characteristics and installation processes is escencial for the life of the Dam and has been followed closely by the quality personnel involved on its procurement, treatment and installation.
The challenges related to the procurement of residual soils started with the depletion of the available material on the project identified sources. Several actions were taken to identify potential sources as soon as it was possible. The existence of the material both in quality and quantity was not evident on most of the cases because of the vegetation cover. For that reason, investigation areas were defined based on the geological information available from ACP engineering division.
This paper focuses on the works and challenges for the construction of the Pacific Access Channel, and intends to document the relevance of these challenges and the importance of effective Project Management.