Waterproofing & Water Control

Glenmont, MD is a suburban community located approximately 12 miles north of Washington, DC. The Glenmont Station is located beneath Layhill Road north of Georgia Avenue and features a center paltform and an arch architecture. The Tunnel alignment runs along Georgia Avenue, a busy street flanked by shopping centers and private homes, and connects the Weathon Station with the Glenmont station. Four ground categories and support classes were developed according to the prevalent geology. The contract allowed for changes to the support elements with the engineer's approval and modifications to the ground support categories were made based upon observations of the ground behavior and the initial lining. Monitoring was performed with a variety of instruments (convergence bolts, inclinometers, extensometers, pressures cells, etc). The tunnel waterproofing system is an integral part of the project design and comprises a PVC membrane on a non-woven geotextile over the whole section from side drain to side drain. This system has ensured a dry Tunnel and Station and provided the owner with low maintenance costs.

The original tunnel was built in 1865 as a 12 ft wide (4 m) single-track rail tunnel. It was widened in 1873 to 25 ft (8 m) double-track with a 26 in-thick (66 cm), brick-lined horseshoe design. After several structural repairs, mainly for spalling bricks, it was finally closed in the early 1960s. More than 30 years later the Port Authority of Allegheny County saw benefits in adapting the former railroad alignment and right of way to its new bus way connection between downtown Pittsburgh and the new Pittsburgh International Airport. A NATM value engineered proposal in the tunnel refurbishment contract provided US $ 2 mil cost savings compared to the original bid. The redesign was based on elevating the tunnel alignment so that the future tunnel crown could be excavated in better ground conditions and on changing the proposed horseshoe to a "rounded" cross section. This combined with the utilization of the NATM allowed a 40 % reduction in shotcrete thickness, a 22 % reduction in concrete lining thickness and the elimination of the reinforcement in the final lining. Furthermore, the NATM proposal eliminated pre-excavation grouting (200,000 bags of cement) and over 10,000 rock bolts while reducing lining thickness. During tunneling up to three headings were excavated simultaneously, one from each portal and one started within the tunnel, averaging a total excavation progress of 15.4 ft (4.7 m) /24h day. Following waterproofing, the concrete lining was completed 16 month after beginning of the reconstruction.

The Russia Wharf segment is the last, but most challenging section of the Silverline Phase II construction for the Massachusetts Bay Transportation Authority (MBTA). The line is designed to provide a dualmode bus rapid transit connection between the central business district in South Boston to the new Convention Center. The tunnel passes diagonally under the 100 year old Russia Wharf complex, which comprises three seven-story buildings with steel frames and brick facades listed in the National Register of Historic Places. The chosen construction method was NATM in conjunction with ground freezing, for the first time in the US. Steel fibre reinforced concrete was used for temporary and permanent lining.

The Bergen Tunnel on the New Jersey Transit network is a double track, horseshoe shaped rail tunnel, built in the 1870s, passing through fractured diabase. Over time, water ingress has caused operational problems. In 2000 the owner decided to undertake major structural rehabilitation. The brick lining was stripped out and the original profile was enlarged to take a new reinforced in-situ concrete lining and drainage system. Old ventilation shafts were backfilled. Two large openings were retained for tunnel ventilation, emergency access and to house new power and electrical substations.

Leak remediation measures at the East and West Connector to the Mezzanine Level of City Place Station. Measures consistend of joint and crack grouting, the installation of a felxible membrane lining on the structural concrete lining and a cleaning of the existing drainage system.