American Underground-Construction Association's Featured Project

Industry News

Each month AUA will feature an outstanding Underground Project currently under construction, featuring its unique aspects in terms of technology, location, function, etc. Contact AUA to nominate projects.

This month's Featured Underground:

Tren Urbano

San Juan, Puerto rico


Phase I of the Tren Urbano Transit System (Río Piedras Contract in yellow)

Tren Urbano – Río Piedras

Phase I of the Tren Urbano project, a new transit system to serve San Juan, Puerto rico, is a 17.2 km route which will connect Bayamon, Guaynabo, Rio Piedras, Hato Rey and Santurce. The estimated travel time between the furthest points is 30 minutes. There will be 16 stations strategically located in commercial and residential areas with the highest population density and greatest traffic congestion. Major uses such as Centro Medico, the University of Puerto Rico, and government and sports facilities will be connected by the first line. Future extensions will extend to the Government Center of Minillas in Santurce, the International Airport Luis Muñoz Marín, and Old San Juan. The system features electric trains that will run on a combination of elevated alignments and subway.

Rio Piedras Subway Segment

Early in the planning and design process, local agencies and citizens requested that the historic Rio Piedras section of the city be protected during and after construction by putting the alignment underground.

The 1500 meter-long Rio Piedras segment of the Tren Urbano project has been designated by the Federal Transit Administration (FTA) one of five turnkey demonstration projects for testing procurement procedures which shorten schedules and control costs.

The firm of Daniel Mann Johnson and Mendenhall (DMJM) was engaged by Tren Urbano to provide a design for 30% of the Rio Piedras project. This allowed for a tender to be issued for the design and build of the first section of the new system.

Three joint ventures bid on the project. The bid of KKZ-CMA of US $225,600,000 was deemed the best value and an award and notice to proceed was given in April, 1997. KKZ-CMA is comprised of Kiewit Construction; Kenny Construction; and H.B. Zachry Company; CMA, a San Juan based engineering design firm, and engineering firms Jacobs Associates, Sverdrup and Woodward Clyde. Jacobs Associates is providing all tunnel design.


The Rio Piedras segment consists of twin EPBM tunnels; NATM tunnels; a mined station and a cut-and-cover station. Rio Piedras is very complex due to the density of the area, difficult ground and a high groundwater table. Nearly every type of tunneling and underground construction technology is being employed in its construction.

The Rio Piedras mined station is 150 meters long by 17 meters wide, by 17 meters in height. When complete, it will be one of the largest diameter soil tunnels ever constructed. This structure is being built using stacked-drift mining techniques in which the tunnel lining, consisting of 15 concrete filled drifts, is constructed to form a horseshoe-shaped compression arch. Many factors, including variable soil conditions, relatively shallow tunnel depth (less than five meters), and small permissible ground settlements, have influenced this design and construction approach.

CET399G.jpg (31458
EPBM hole through in North Shaft

Twin Earth Pressure Balance Machine (EPBM) tunnels will be constructed from the north end of the Rio Piedras Station to a cut-and-cover station at the University of Puerto Rico (UPR). The tunnels will be 1405.5 ft. long and 21 ft. in diameter. They will be excavated and lined using one-pass construction. A refurbished Lovat EPBM, which recently completed four tunnels on the Washington Metro’s Congress Heights and St. Elizabeth projects, will be used. All the segments for the tunnel are being cast by Marmolejo Construction.

MT399A.jpg (23380 bytes)
Bayamón Left & Carolina Left NATM tunnels

Two additional tunnels, each 1,282 ft in length, in a 22 ft. oval shape. with two spurs for future expansion, are being constructed south of the Rio Piedras Station, and will connect the underground portion with the system to the south. The tunnels are being constructed by the New Austrian Tunneling Method (NATM), with mesh reinforced shotcrete and lattice-girders utilized for tunnel support.

Extensive grouting is being performed by Soletanche-Bachy along the Rio Piedras alignment to stabilize the many historic buildings in the area and prevent settlement. The system is computerized and constantly monitored for movement along the alignment and making grout corrections as necessary.

When complete, the Tren Urbano project is expected to dramatically improve transportation infrastructure in Puerto Rico, improve air quality and relieve chronic congestion. Phase I is scheduled to begin revenue service in 2001.

The project is being watched closely by FTA and project owners around the U.S. to determine whether design-build offers a viable alternative to traditional procurement for a variety of heavy construction projects.

For more information and construction progress updates click below to visit the Jacobs Associates web site

or click below to visit the Tren Urbano web site