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00EPB Tunnels: Twin-bore tunnels
were constructed between the University of Puerto Rico Station and the
Río Piedras Station. Both tunnels, approximately 430 meters in
length and 6.3 meters in diameter apiece, were excavated with an earth
pressure balance machine (EPB). The EPB machine was used in conjunction
with a "one-pass" precast concrete segmental lining system where
individual segments are bolted and gasketed to form a watertight lining.
The tunnels pass under a historic structure owned by the University of
Puerto Rico, as well as under several occupied buildings. An emergency
cross passage was constructed between the EPB tunnels using the NATM.
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