The Long Island Rail Road (LIRR), the largest commuter railroad in the US, provides the New York Manhattan service to Penn Station on the West Side. Penn Station is currently operating at capacity, imposing serious limitations on future growth. Recognition of this service overstrech dates back to the 1960’s when the Metropolitan Transportation Authority (MTA), parent company of the LIRR, developed a plan to provide an East Midtown Terminal for the LIRR. In the 1960’s and 1970’s New York City Transit Authority (NYCTA) acting on behalf of the MTA constructed a 2.6km tunnel under the East River extending from 63rd Street and 2nd Avenue in Manhattan under the East River to 29th Street and 41st Avenue in Queens. This was later extended a short distance as part of the 63rd Street Connection Project by NYCTA.
In 1993, a study was initiated by the LIRR to develop the physical, environmental, and operational feasibility of the project. The preferred alternative is an ambitious $4.3bn connection of the Main Line and Port Washington Branch to Grand Central Terminal to be completed by year 2011.
Employment in New York is rising and is expected to grow by 17% within the next 20 years resulting in the trip from Long Island growing by up to 24%. Currently, the LIRR operates 36 trains per hour during rush periods to and from Penn Station carrying about 212,000 commuters each way. The station which serves Amtrak, NJ Transit, and LIRR, is at capacity with plans to increase services over the next few years. The East Side Access project will improve the mobility in the region, and relieve congestion in Penn Station. LIRR is planning to operate 24 additional trains per hour during the morning and evening rush periods to Grand Central Terminal in addition to the 36 trains operating to Penn Station. This will increase its service capacity from about 109,000 to 321,000 passengers to and from Manhattan. In addition, the project will provide a single seat journey to most and will reduce overall travel time by about 30 minutes each day. Above all, the project will stimulate economic growth in Manhattan and Queens.
The planned project begins at Harold Interlocking adjacent to Sunny Side yard in Queens. Harold is one of the busiest railroad interlockings in the US with over 540 train movements per day. Within the limited confine of this space, the alignment enters a series of tunnels under Sunny Side Yard. The alignment in Queens extends about 1.8km from the existing bulkhead near 29th Street and 41st Avenue across Northern Boulevard and connects to LIRR’s Main Line and Port Washington Branch. The existing two track tunnel branches into a four track configuration which, in turn, connects to the Harold complex east of 43rd Street passing across and underneath Yard A and Sunnyside Yard. In order to provide midday storage capacity, lead tracks will be provided to Yard A. The alignment in Manhattan starts at the corner of 2nd Avenue and 63rd Street where the existing tunnels are terminated about 50m underground and extends south-westerly to Park Avenue and connecting to Grand Central Terminal under Park Avenue and 48th Street. The tunnels start as two single-track tunnels which separate through two wye caverns into four single-track tunnels, these then vertically separate until they can be brought into two one-over-one caverns. The tunnels then converge to a two-level diamond crossover and then separate again through two bi-level wye caverns into four two-level structures that tie into the end walls of the station caverns.
The LIRR Station will be situated under the historic Grand Central Station and will consist of two caverns having eight tracks (two-over-two in each cavern) with four island platforms. The caverns are situated between 44th and 48th Streets approximately 52m below street surface. The cavern dimensions are 18.3m wide by 20m high and approximately 365m long. They are located 30.5m on centres beneath Park Avenue and operating underground Metro North Railroad tracks. The alignment crosses several existing transit lines including the 63rd Street line, the 60th Street N&R lines, the IRT Lexington Avenue line, and the 53rd Street E&F lines. In addition, along Park Avenue the alignment runs under the Park Avenue Tunnel for the Metro North Commuter Railroad.
Geotechnical conditions
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By GlobalDataGeotechnical considerations are the key elements to the successful design and construction of the predominantly underground Grand Central Connection project. Most of the construction will be in rock known as Manhattan Schist, a foliated (thinly bedded) metamorphic rock with high compressive strength. Overlying Soils consist of fill, various types of glacial soils, and alluvial soils associated with former streams draining to the East River.
The excavations in Queens will be predominantly in soil. Some excavations in the Ravenswood Gneiss will be encountered in the open cut as well as the initial segments of the bored tunnels. The soil deposits in Queens represent a complex glacial depositional environment upon which a post-glacial tidal marsh environment and man-made fill deposits were superimposed. The soils in the area are:
Tunnelling issues
The selection of an appropriate tunnelling method for each section of the alignment will have a major impact on the successful completion. A number of factors have been evaluated including: ground conditions, groundwater, geometry and site constraints, impact on adjacent structures and utilities, environmental concerns, local construction practice, community acceptance, cost, schedule, and contracting practices.
In Queens tunnelling will be in soft ground composed of glacial deposits, and till. Lowering the groundwater will have severe adverse effects on adjacent structures and utilities and will not be acceptable environmentally.
The presence of contaminated groundwater and hazardous material in Sunnyside Yard further impact the selection of the tunneling method. To deal with these issues, an EPB or slurry TBM will be used, bored tunnels will have a 5.9m i.d and will be constructed using a single pass gasketed segmental liner. Each ring will be 1.5m long and consist of five typical segments plus a key. The 254mm thick segments will be bolted to form a ring behind the shield and the connections will be by dowel.
At the launch shaft, the tunnels will be in mixed face for a distance of about 50m and they will be no further apart than 1.5m. Hence, special measures in ground treatment and TBM design.
Because the cut and cover tunnel will be built in close proximity to existing structures and contaminated ground, such as at the Sunnyside Yard, for instance, a rigid, impervious excavation-support system, using slurry walls and jet grout walls will be used.
Crossing Northern Boulevard will require underpinning of the IND Queens Boulevard Line subway box structure and the elevated BMT line. This work can be done by one of two methods such as the “pit method”, and the “mini-piles method”. This way the work can be accomplished from the exterior of the box with little or no interruption of existing services. In the “pit method”, small drifts and underpinning pits will be excavated under the box and filled with concrete to support it. The area between the drifts will then be excavated to construct the LIRR tunnels.
In Manhattan, the two most appropriate tunnelling methods would be drill and blast or TBM. The selection of the tunneling method took into consideration environmental issues and public acceptance. Due to the geometrical configurations of the alignment in Manhattan both methods will be used. The drill and blast method has a negative perception by the public because of noise and vibration etc. On the other hand, although a TBM may have a better public perception, the logistics of getting the TBM into the ground may be difficult and would require construction of a shaft in Manhattan, both costly and disturbing to the neighbourhood. To address these issues, it was decided to eliminate a construction shaft in Manhattan and replace it with a shaft in Queens as part of the cut and cover construction. All materials will be brought in via the shaft in Queens and through the existing tunnels. Similarly, the muck will be removed using conveyors or hoppers through the existing tunnels to Queens where it will be hauled away using freight trains from the existing Rail Yard. The construction of the Manhattan tunnels begins at the western terminus of the existing 63rd Street Tunnels located beneath the intersection of East 63rd Street and Second Avenue. The tunnels will be two single-track circular cross section, spaced approximately 10m on centers to be constructed by TBM. The tunnels will have a variety of cross section configurations from a circular to single track horse shoe structure to wye structure, to two level wye to two track stacked, to four track stacked structures. They will vary in dimensions from 5.6m diameter to 17.1m by 15.85m. Two TBMs will be required and each will excavate two tunnels through the entire alignment passing through various structural configurations to the southern end of the station caverns. The remaining portions of the alignment will be constructed by controlled blasting to minimise overbreak. The cross over caverns and the wyes will then be enlarged. The LIRR Grand Central Terminal consists of two caverns that are served by four centre-island platforms. Cross section of the 365m long caverns is about 18.3m wide by 20m high. The caverns are located partially beneath two landmark buildings, the Helmsley and the Met-Life buildings, and are interconnected by four cross passages. Each cavern houses a lower two-train chamber, an upper two-train chamber, and a mezzanine circulation/waiting area on a mid level between the upper and lower train rooms. Each train chamber is provided with an 8.3m wide centre platform 311m long. Three ventilation tunnels of variable widths and service corridors and elevator passages are provided. The cross passages and the ventilation tunnels intersect the upper half of the cavern cross section, interrupting the cavern arches. The construction of the caverns will require state-of-the-art design and construction under highly developed real estate with limited rock cover.
Conclusion
Never before has a single project offered such enormous opportunities for expanding rail market share while affording economic and environmental benefits to customers and the public. The $4.3bn budget project faces great technical, and financial challenges. To achieve the objectives will require spirited vision, broad planning, state-of-the-art design and construction techniques, and above all sensitivity to the environmental and the community issues.
Related Files
Cross section of a Manhattan horseshoe, four track tunnel
Four track Manhatten running tunnels
Map of Manhatten and Queens
