Fast and innovative mode of transportation in the Northeast Corridor — tunneling challenges

The Superconducting Maglev (SCMAGLEV) project is a proposed high-speed train system between Washington, D.C. and the city of Baltimore, MD, approximately 60 km (37 miles) long (Fig. 1). The segment from Washington, DC to Baltimore is the first leg of a route that eventually will be between Washington, D.C. and New York City. The envisioned route would include additional stations in Wilmington, DE and Philadelphia, PA, as well as at additional major airports along the route. With the Northeast Corridor (NEC) home to 17 percent of the U.S. population, and travel between the major cities of the NEC predicted to increase 115 percent by 2040, the SCMAGLEV is a technology that can help reshape transportation and commerce in the NEC and the United States.

The SCMAGLEV system operates using a combination of electromagnetic levitation (support), propulsion and lateral guidance rather than flanged wheels, axles and bearings as in conventional high-speed rail systems. The train system will cross several transportation corridors including interstate highways (I-95, I-195, MD 295 Baltimore-Washington Parkway, I-595, I-695, I-895), several state, city and local routes and railroad lines, as well as the Baltimore/Washington Thurgood Marshall International (BWI) Airport, with all crossings gradeseparated. The project developer is the Northeast Maglev/ Baltimore Washington Rapid Rail (TNEM/BWRR) with WSP as the prime consultant and Gall Zeidler Consultants as the tunneling subconsultant.

An Environmental Impact Statement was initiated in the fall of 2016 in accordance with the National Environmental Policy Act with the Draft Environmental Impact Statement (DEIS) was expected to be published in in mid 2020 and the Final Environmental Impact Statement (FEIS) and Record of Decision (ROD) by mid- 2021. Construction is envisioned to commence in 2021 with an estimated total cost of more than $10 billion.

Technology

The Baltimore-Washington Maglev Project provides new infrastructure, stations and facilities for a SCMAGLEV train system. The project will build on the safety practices and culture of system developer Central Japan Railway Company (JRC), which has operated the Tokaido Shinkansen bullet train between Tokyo and Osaka without a single fatality since 1964. JRC applied a similar safety approach to the development of the SCMAGLEV system. SCMAGLEV was certified by the Japanese government and has been in commercial operation since 2014. Safety systems for the Baltimore-Washington Maglev project will be developed through a collaborative process with the Federal Rail Administration Office of Safety and local emergency response forces.

The primary elements of the project include superconducting magnetic levitation rolling stock and systems, using a proprietary technology developed by CJRC and two guideways, borne by tunnel and viaduct structures. The system deploys technologies that are new to the United States or of previously limited application, including most notably an electromagnetic propulsion system. This technology is capable of accelerating trains to a top cruising speed of 500 km/h (311 mph) in approximately two minutes and allows for a driverless train operation. Additionally, the energy consumption for the train is far less than that of other ultra-high-speed travel options, such as a Boeing 777, or the operational Maglev in Shanghai China (Fig. 2). The train utilizes superconducting magnets for acceleration and lateral guidance of the train. It is estimated that the total trip duration from Washington D.C. to Baltimore will be 15 minutes and Washington, D.C. to New York City will take one hour, at a speed of 311 mph (511 km/h).

Alignment alternatives

The project is located in Washington, D.C. and Maryland, traversing a distance of approximately 60 km (37 miles) with three stations in Washington D.C., at BWI Airport and in Baltimore. The Washington, D.C. and BWI Airport station options are underground. There are aboveand below-ground options for the Baltimore station. The SCMAGLEV system requires an independent and secured grade-separated right-of-way. Further, assuring the safety and comfort of passengers requires use of predominantly straight geometry with limited horizontal and vertical curvature consistent with the physical dynamics of ultra-high-speed travel. To accommodate the range of topographical and surface features, existing dense urban areas, utility mains and existing structures, the proposed construction is expected to consist of a below-ground structure(tunnel) for approximately 75-80 percent of the route, and elevated structures (viaduct) for the remainder. The train system incorporates two main guideways, three stations, one trainset maintenance facility, electrical substations, tunnel ventilation plants and emergency egress.

The environmental review process narrowed two alignment alternatives that generally follow the Baltimore- Washington Parkway (MD 295) (Fig. 3a), with a preferred alternative to be named in the DEIS in 2020. Preferred alternatives for station locations in Washington, D.C. and Baltimore will be named in the DEIS as well. At BWI Airport, the existing hourly parking garage will be demolished for station construction, with a replacement parking garage to be constructed prior to demolition of the existing one. The stations will have a platform length of approximately 400 m (1,312 ft), enabling accommodation of 16-car trains.

Ground conditions

A preliminary geotechnical exploration program was conducted along the two alignment alternatives in the spring and summer of 2018 and included 22 boreholes and geotechnical testing (Figs. 3b, 4). The program provided a preliminary look at the anticipated ground conditions for construction and tunneling along the alignments, and identified target areas of interest for the next phase of geotechnical investigation.

The proposed alignments are located within the Coastal Plain Physiographic Province, consisting of relatively soft strata. These strata lie on top of crystalline bedrock and thicken to the southeast on the order of approximately 150 m (500 ft) per 8 km (5 mile). The strata consist of sedimentary deposits of the Cretaceousage Potomac Group, which includes clays, sands and gravels and Holocene-Pleistocene terrace gravels and loose granular soils. All sedimentary formations sit unconformably atop each other, with the oldest sediments (Patuxent Fm.) sitting unconformably atop bedrock. Bedrock ranges in age from Jurassic to Cretaceous and is exposed or encountered at shallow depths at the Fall Line, which is the boundary between the Coastal Plain and Piedmont physiographic provinces.

Ground water conditions are expected to vary widely across the alignments, from dry conditions to ground-water levels ranging from relative shallow depths of less than 3 m (10 ft), to depths in excess of 12 m (40 ft). Fluctuations in ground water levels across the alignment will occur seasonally due to variations in rainfall, evaporation, construction activity, surface runoff and proximity to adjacent streams and the Chesapeake Bay shoreline. Localized perched groundwater and isolated watersaturated sediment lenses can also be expected. Connectivity of the aquifers to rivers and creeks has been identified in various locations.

Tunneling is expected to occur primarily through the Patapsco, Arundel and Patuxent formations of the Potomac Group soft ground for most of the alignment. Bedrock was encountered in boreholes at portions of the alignment closest to the Fall Line, which includes the Washington, D.C. and Baltimore stations, as well as the central portion of the alignment alternatives approximate to the viaduct segment. Locally higher sections of the bedrock cannot be excluded, and would be a target of the next phase of geotechnical investigations. No unanticipated or abnormal geological features were encountered during the preliminary ground investigation program.

Tunneling challenges

The proposed alignment alternatives include approximately 40 to 45 km (28 to 30 miles) of generally deep tunnel sections. Considering the length of the tunnel sections and the required uniform geometry, it is anticipated that mechanized tunneling will be implemented for the majority of the alignment that will need to address the following challenges:

• Tunneling in soft ground, consisting of sands, silts, clays and gravels.
• High ground water level.
• Tunneling across urban areas and therefore under major infrastructure.

Considering the soil types and groundwater conditions expected along the deep tunnel sections, which require an active face support, the use of a closed-face tunnel boring machine (TBM) will be required. Based on the available preliminary information on the geological and hydrogeological conditions and the critical impact of groundwater to the tunneling activities, implementation of earth pressure balance machines (EPBM) is considered, at this stage, most appropriate for the anticipated subsurface conditions. Alternatively, slurry and/or mix shield TBMs could be considered, as the alignment could encounter sections of mixed geology with hard rock potentially shallower at the two ends of the alignment, pending the next phase of ground investigations. The information acquired from the additional ground investigation program will be used to evaluate and select the TBM type and refine specifications.

TBM tunnels in soft ground are generally supported by pre-cast segments, which are erected at the tail end of the TBM, producing a continuous lining over the tunnel length with a circular, uniform geometry. Segmental linings will be equipped with gaskets in the joints between the segments to inhibit groundwater inflow into the tunnel.

To minimize the construction footprint of the project and minimize surface disturbance and construction impact, while taking into consideration the spatial requirements for the train operation, a single-bore TBM tunnel with an outside diameter of approximately 15 m (50 ft) was considered as optimal compared to twin-bore tunnel configuration (Fig. 5a). Although tunneling with a largebore TBM is a challenge in itself, the technology and capabilities of present-day TBMs allows for unimpeded tunneling and enhanced risk management. Within the past 10 to 15 years, large-bore TBM tunnels are an increasingly common option being utilized for major transportation projects, with recent successes on the Port of Miami Tunnel in Miami, FL (Bauer et al., 2013), Barcelona Metro Line 9 in Barcelona, Spain and the Shanghai River Crossing in Shanghai, China. Additionally, the alignment had been determined such that TBM tunneling would be performed under at least one tunnel diameter of ground cover to minimize surface impact.

Subdivision of the TBM tunnel alignment into sections with a length of 5 to 6 km (3 to 4 miles) is currently considered for enabling concurrent boring along various sections and providing flexibility for contracting and packaging of the project. This requires construction of additional launch sites, which are typically cut-and-cover structures. In areas where space restrictions do not allow for construction of launch boxes, launch shafts of adequate size are considered as an alternative. Ventilation shafts are planned to be used as launch shafts where possible to minimize cost and streamline construction. As the launch sites will be also used for stockpiling of the spoils, implementation of additional launch sites along the alignment will allow more efficient storage and transport of the spoils to the areas designated for disposition.

Short sections of cut-and-cover tunneling will be used for the stations and the transitions between the viaduct and TBM tunnel sections, including portals and TBM launch locations. Implementation of cut-and cover tunneling requires installation of excavation support of slurry walls, bored pile walls, soldier pile and lagging or shotcrete. The method of support of excavation (SOE) chosen will also be dictated by the local ground conditions, with slurry walls a likely choice where dewatering of the sediments is to be avoided to prevent settlement of any adjacent existing structures. Depending on the limits of disturbance, generally tie-back support or internal strutting is expected for deeper excavations. A waterproofing system will be installed to prevent groundwater inflow into the tunnel in the final permanent stage.

Due to the dense urban environment in Washington, D.C. and Baltimore, and the relatively deep alignment, construction of the stations with minimal surface impact and disruption to the city activities will be challenging and will require a well-planned design. Similarly, construction of the station under the BWI Airport without disrupting airport operations will pose a significant undertaking.

Fire and life safety

Design, construction and operations for the SCMAGLEV will be planned with a safety focus: safety of the traveling public, the construction and operations workforce and the adjoining communities that are impacted by the construction and operations of the system. Each area will be addressed in the planning and design of the infrastructure, core systems, facilities and operating and maintenance practices for the SCMAGLEV system.

Fire and life safety have been given full consideration and attention in the design since the inception phase of the project. Fire and life safety considerations factor into all aspects of the system design, including linear infrastructure (viaducts and tunnels), passenger stations and operations and maintenance facilities. The fire and life safety include elements and layout of egress and access paths in the tunnel system and definition of design fires for vehicles, cables and other equipment.

The design standards and guidelines addressing fire and life safety requirements for the structures of the project are:

• NFPA-130.
• NFPA-101.
• NFPA-502.
• Americans with Disabilities Act.
• Accessibility Guidelines (ADAAG).
• Maryland Building Performance Standards.
• Maryland State Fire Prevention Code.
• Washington D.C. Building Code and Construction Code.

To meet the requirements of the standards for Fire and Life Safety and NFPA-130, in particular, a safe emergency egress for passengers to a point of safety will be provided in the underground sections. This would be achieved by utilizing an escape walkway/gallery inside the tunnel envelope located below the guideway (Figs. 5b, 6a). The considered tunnel cross section provides sufficient space below the guideways to be used as an emergency evacuation chamber. The escape gallery would have an independent ventilation system in the event of a fire or other emergency and would have surface access via ventilation plants and shafts envisioned along the underground section of the alignment at an approximate distance of 5-6 km (3-4 miles) (Fig. 6b).

Due to the unique characteristics of the SCMAGLEV system, the standards and guidelines listed will be supplemented by Japanese codes and practices that have contributed to that country’s exemplary safety record. Safety systems and practices researched and developed by JRC specifically for the SCMAGLEV system will be proposed for incorporation into the proposed project to ensure that the highest standards for safety are deployed.

Outlook

With the successful completion of the preliminary ground investigation program, the Draft Environmental Impact Study is underway with Record of Decision (ROD) anticipated in 2021. A positive ROD would mean forward movement on the next phase of ground investigation and preliminary engineering, with construction envisioned to commence in 2021 at an estimated total cost of more than $10 billion, which is less than for conventional highspeed rail. Long-term maintenance costs of the system are minimal because there is no mechanical contact and wear between the train and the guideway.

The proposed SCMAGLEV is a technically challenging but innovative project that will shorten commuting time between Washington DC and Baltimore, and later to New York City. The project will enhance mobility along the northeast corridor and could spur development and economic growth in the region.

References

Baltimore-Washington Rapid Rail. 2018. https://bwrapidrail.com. Bauer, A., Gall, V., and Bourdon, P. 2013. Comparison of Predicted Versus Observed Structural Displacements of Existing Structures at the Port of Miami. In Proceedings of the Rapid Excavation and Tunneling Conference 2013, Edited by M.A. DiPonio and C. Dixon. Englewood, CO: SME. The Northeast Maglev. 2018. https://northeastmaglev.com.