Tren Urbano—Río Piedras Contract

Serving San Juan’s 2.5 million residents, the Tren Urbano (“Urban Train”) stretches 10.7 miles (17.2 km) with 16 stations. The Río Piedras section is the only underground portion of the Tren Urbano system and is located beneath a dense, historic urban area and consists of guideway tunnels and two stations in soft alluvial soils under the water table.

As part of the design-build team, Jacobs Associates was responsible for providing all tunnel structural design. We designed twin tunnels 21 feet (6.4 m) in diameter and 1,400 feet (430 m) in length to connect the two underground stations. The tunnels were excavated with an earth pressure balance machine used in conjunction with a one-pass precast concrete segmental lining system. In addition, a complex rail turnout consisting of 4 tunnels was constructed by the New Austrian Tunneling Method, with some of the tunnels located less than 3 feet (1 m) from each other. Reinforced shotcrete and lattice girders were used for initial tunnel support, followed by PVC membrane waterproofing and a cast-in-place final lining.

Probably the most complex and interesting portion of the project was the Río Piedras mined station, 62 feet (19 m) wide, 52 feet (16 m) high, and 490 feet (150 m) in length. One of the largest diameter soil tunnels ever constructed, this structure was built using the stacked drift method, in which the tunnel lining, consisting of 15 individual tunnels backfilled with concrete, forms a horseshoe-shaped arch.

Representing six years of intensive efforts and a high level of cooperation between Jacobs Associates and the contractor, Kiewit-Kenny-Zachry, the project was delivered well ahead of the aboveground contracts.