East side access project’s Queens Tunnel S.K. Sarkar Parsons Brinckerhoff W.S. Lee Parsons Brinckerhoff
ABSTRACT: The East Side Access Project (ESA) with a budget of $4.3 Billion will be the largest tunnelling project ever undertaken in New York. Long Island Rail Road (LIRR) service to New York’s Penn Station, on the West Side of Manhattan, is currently operating at its capacity. The ESA project will provide direct rail connection from Long Island to Manhattan’s Grand Central Terminal on the East Side, and add capacity. In Queens, construction comprises comprises of cut and cover tunnels t unnels starting from the existing subway tunnel and then changing to six soft ground bored tunnels and cut and cover approach tunnels leading to the LIRR Main Line tracks. This paper discusses site investigation, ground conditions and design development for various construction elements.
1.INTRODUCTION The LIRR is the busiest suburban commuter railroad in the U.S., serving about 269,000 passengers on 740 trains a day in the year 2000. Its capacity to bring additional passengers to Penn Station is severely restricted due to physical limitation at Penn Station and the anticipated ridership growth of Amtrak and New Jersey Transit, the other users of the station. This restriction and final Eastside destination of a large number of riders, provided impetus for an East Side Terminal for LIRR (Fig 1). The ESA will provide 24 peak hour trains into the new terminal increasing LIRR service to Manhattan by about 109,000 passengers.
Manhattan
The planning of ESA project dates back to 1960’s when the Metropolitan Transportation Authority, the parent company of LIRR, authorised New York City Transit Authority (NYCT) to construct 2,560m tunnel under the East River. The upper level of this two- level, four-track tunnel, completed in 1970’s, are being used by NYCT subway trains. The two currently unused lower level tracks will be used for ESA trains. One major challenge of this project is to minimise impacts on the overlying operating facilities, which include NYCT subway and elevated lines, Amtrak’s Sunny Side Yard (SSY), LIRR Main Line tracks (also used by Amtrak’s North East Corridor service) and roadway bridges crossing the alignment. Another challenge is not to disturb the groundwater regime, which may in turn dis turb known contaminant plumes within Amtrak’s property.
Queens
Figure 1:
Location Plan
2. PROJECT DESCRIPTION The Queens tunnels construction will start with an open cut adjoining the existing NYCT 63 rd street connector subway structure (Fig 2). Initially this open cut will be used for TBM access for Manhattan tunnels and later along with the larger cut and cover excavation will be used for mucking. The next section of construction involves under unde rpinning of the NYCT IND subway box and the elevated BMT line columns within the limits of Northern Boulevard, a major thoroughfare in Queens. The underpinning will allow construction of the proposed ESA tunnel. Once constructed, it will support the IND box. The following section is a cut and cover st ructure primari primarily ly throug through ha lightly used rail yard. The cut and cover excavation is approximately 260m long, 30m to 67m wide and 18m to 21m deep. The western half of this excavaexcava tion will provide an exit portal for muck removal from Manhattan tunnels and caverns. The eastern half will serve as a launching site for the six soft ground tunnels and used for muck removal. The bored tunnels commencing from the cut and cover section curve under SSY, one of the busiest rail yards in the country, due East and terminate at “transition structures’ within the Harold Interlocking where 1200 trains a day pass overhead at up to
Figure 2:
Project Alignment
90Km/h speed. Each bored tunnel is approximately 670m long with depth of cover varying vary ing from from 9m at the launch shaft to less than 2m at the TBM exit portals. Transition structures start as cut and cover construction, and become U-structure terminating at grade where track connections are made with the existing LIRR tracks. Each transition structure is approximately 305m long exc ept the inbound/outbound lead, which is about 463m long. Emergency exit structures for the revenue tracks are provided with staircases exiting onto Honeywell Street Bridge, approximately midway of the bored tunnel section. For the non- revenue tracks, the inbound and outbound tunnels, an emergency exit is provided at 39 th Street Bridge. Relocation and protection of bridge foundations are needed. 3. GROUND CONDITIONS 3.1 Site Investigation The subsurface information at the project site is derived from over 140 geotechnical borings and data from existing sources. In addition to standard split barrel samples, undisturbed samples were co llected by fixed piston and Denison/Pitcher samsam-
plers. Groundwater data were collected from a large number of observation wells installed or existed at the site. Laboratory testing was performed on soil, rock and groundwater samples. A field pump test is planned at the existing rail yard.
Stratum Stratum 8 - Organic Deposits: This stratum consists of highly hi ghly fibrous to woody peat and organic silt. This deposit was found only along the Old Dutch Kill Creek that existed at the site before it was filled.
3.2 Site Geology
Strata 2 to 4 - Mixed Glacial Deposits: The group contains glacial deposits, lacustrine deposits and glaci glacio o -fluvial -fluvial deposits. Because of the t he nature of the depositional process, these soils exhibit a high degree of inter layering and spatial variation.
The project site is located near the physiographic province boundary between the Manhattan Prong and the Atlantic Coastal Plain. The site is underlain by metamorphic rock, which is covered by Pleistocene glacial and inter-glacial inter-glacial deposits as well as postglacial deposits. The Terminal Moraine of the last Wisconsin ice advance, a prominent morphological feature on Long Island, is located approximately three miles southeast of the site. Bedrock consists mainly of gneisses and schists with pegmatite sills and dykes scattered throughout the rock mass. The most common rock type is granitic gneiss comprised principally of quartz, biotite and feldspar. feldspar. The last glacial advance into the Metropolitan New York area is the source of most of the soil deposits and the present surface morphology. 3.3 Interpre Interpreted ted Ground Ground Conditio Conditions ns The glacial deposits above the bedrock can generally be divided into three groups, mixed glacial deposits, glacial till, and outwash/reworked till deposits. Each group is subdivided into several strata. Stratification is generally complex, and significant variations in the thickness and location of the individual units are common. Boundaries between strata are not clearly defined in many cases and considerable inter-layering inter-layering of the glacial materials, particularly in the mixed glacial deposits found at the rear of the Terminal Moraine. Under such environment, different processes of deposition occur during cyclical periods of advance and retreat of the ice front. Prior deposits are re-worked and new new materials are deposited. Overlying the glacial deposits is a layer of man made fill. Peat and organic silts are found within the limits of post-glacial streams in low-lying areas. The stratigraphy of the project area beginning at the ground surface is presented below. Stratum Stratum 1 - Fill: It consists of a heterogeneous mixture of sands, with silts, gravels, cobbles and miscellaneous debris such as brick fragments, wood, concrete and rubble. Some of the fill is b elieved to be excavated glacial materials from strata 2 and 3.
Stratum 2 is predominantly granular with nonplastic to low plastic fine materials. materials. Stratum 3 co ntains more fines than stratum 2. Stratum 4 contains significant amount of fines, mainly non-plastic silts to clays of low plasticity and occasionally sand and gravel. Stratum 5 - Glacial Glacial Till/ Reworked Till: These soils consist of heterogeneous mixture of sand, silt and gravel, mostly without a cohesive binder. A large number of boulders were encountered in this layer. Mixed with the till are outwash materials that are predominantly sand with little fines. Stratum 6 – Decomposed Rock: This stratum consists of very stiff to t o hard silts, silt s, clays and sands. sands. The materials exhibit relict structures of the parent rock. Decomposed rock was found in localised areas, generally thin but it was found to be 8m thick in one area. Stratum 7 – Bedro Bed rock ck:: Bedrock at the site is predominantly fine to coarse grained, unweathered to moderately weathered strong to very strong gneiss and schistose gneiss with RQD generally between 50 and 100 percent. A typical stratigraphy at the bored tunnel section is shown in Fig 3. 3.5 Hydroge Hydrogeolog ologyy The groun groundwate dwaterr at the si te is within an unconfined aquifer formed in the glacial deposits directly overlying the bedrock. The primary source of the regional groundwater is precipitation, which averages about 120cm a year. Actual precipitation reaching the water table is less than 50 percent because of surface development and drainage char cha racteristics. The regional groundwater flow is northwest toward the East River. However, the groundwater from the site flows primarily southwest towards the New Ne wton Creek.
Till
Figure 3:
Subsurface Stratigraphy
Figure 4: Access Shaft and Cut and Cover Area Plan
4. TUNNELING CONSIDERATIONS 4.1 Access Access Shaft Shaft for Manhattan Manhattan TBMs TBMs The access shaft is constructed between the opera ope rattrd ing NYCT 63 street connector subway tunnel at the Bell mouth structure and the NYCT IND subway tunnel (Fig 4). Opening will be made through the Bell mo uth structure allow ESA construction construction.. The excavation will expose one side of the structure creating unbalanced condition and need to be supported (Fig 5). The construction will also need sheet piling above the tunnel structure to facilitate excavation. excavation. Dam Damage age to the existing e xisting Bell mouth structure should be avoided. On the other end of the excavation settlement under the IND subway and the elevated BMT structure columns are to be kept under tolerable limits. NYCT agreed to a settlement threshold of 12.7mm under the subway tunnels. 4.2 Underpinning of IND Subway Tunnel
The ESA tunnel constructed beneath the IND subway necessitates underpinning of the IND structure (Fig 6). Once constructed, loads from the t he IND and BMT structures can be transferred t ransferred to the newly constructed ESA tunnel. Two different underpinning methods were studied, the pit method and a micro pile method. The later method is selected for design. In this method, piles are drilled from the street surface through the roof and floor of the IND tunnel into the underlying bedrock. The excavation is done between two walls. Because dewatering is not allowed the walls must be watertight. The
Figure 5: Section at Access Shaft
South wall is a jet-grouted wall (Fig 7). Jet grout wall is constructed from the surface similar to piles. The North wall is within existing slurry wall system used for the 63 rd street connector tunnel construction. A soldier pile and lagging system is proposed for this wall. 4.3 Cut and Cover Construction The major challenge here is to avoid any impact on the groundwater regime in turn not to disturb known contamination plumes nearby. The slurry walls will be keyed into bedrock and the rock mass below the wall grouted to reduce the t he seepage into the excavation. A typical section through the cut and cover construction is shown in Fig 8. Threedimensional groundwater model was performed simulating the excavation and dewatering inside of the excavation. The results indicate that lowering of the groundwater behind the slurry walls can be limited to 0.62m, which is acceptable to the regularegu latory agencies. Another challenge is the TBM launch wall. Six TBM tunnels, each 6.6m in diameter, approximately 8.5m on centres, will cut through the launch wall, which is about 21.6m deep (Fig 9). In addition to the earth loads, it must carry load load from 20.5m of water, as dewatering is not allowed outside of the excavation. The design of a slurry wall and an internally braced system is impractical. Various alternative walls with or without ground improvement system are studied. st udied. A jet -grou groute ted d mass to act as a gravity wall appears to be a viable and cost effective option. Further investigations are required for selection of a launch wall system.
Figure 6:
IND Subway Underpinning
Figure 7: Section Through Underpinning Walls
Figure 8:
Section Through Cut and Cover Area
4.4 Soft Ground TBM Tunnels In order to minimise impact to the operating rail facilities, t wo Amtrak tracks tracks adjacent to the launch wall, numerous tracks in the Sunny Side Yard and the LIRR tracks at Harold interlocking, interlocking, it is considered that a pressurised face tunnel boring machine be used which can control ground deformadeformation within acceptable limits. The machine can be either a slurry machine or an earth pressure balance (EPB) machine. The TBM will have to be cac a-
Figure Figu re 9:
Section Through TBM Launch Wall
pable of dealing with the anticipated rock in the invert in about 10% of the alignment as well as dealing with random boulders along the alignment. A slurry machine will have a rock crusher installed in the plenum and the EPB will be fitted with bars limiting the size of boulders entering the shield. For both machines, strategically located disk cutters can be installed on the face to break bedrock or large boulders. A small built-in compressed air chamber may be needed to permit inspection and maintenance of the cutting tools t ools or to remove obstructions.
4.5 Transition Structures One pass bolted and gasketed concrete liners will be designed. Elastomeri Elas tomericc gaskets are cons consid ider ered ed for installation into groves with zero dimensional tolerance on the four sides of the segment to make them completely watertight. Pre fabricated steel segments are considered to form penetrations at the emergency exits.
Figure 10: Section Through Transition Structure
Cut and cover transition structures are needed to bring the tracks from the end of the bored tunnels to the final grade Fig 10). These would extend eastward from the TBM reception pits. The location of the tunnel approaches is dictated by the position sition of the existing tracks. The approach stru ctures are widened at TBM reception pits adjacent to the exit portals to allow for TBM demobilis demobilis ation. Slurry walls and secant pile wall are considered for the reception pits and the approach strucstru ctures.
