The 4.5km-long tunnel is the first in the country to pass under the Panama Canal and Panama Metro described the achievement as “an unprecedented milestone”.
“With 44% of total progress, the project continues its unstoppable march,” the organisation said.
The tunnel passes beneath the Panama Canal at 65m below sea level.
Since excavation began a year ago more than 1,000 lining rings have been installed. Last month TBM Panama achieved the erection of 149 rings, corresponding to 298m of tunnel advance in one month.
Excavation continues to advance towards Balboa Station where TBM Panama will undergo scheduled maintenance early next year before completing the final section of the tunnel.
The mix shield TBM, which has a 13.51m diameter and is 93m long, was designed to adapt to the unique geological conditions of the Canal area.
