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Project Overview
Project History
Project Overview
Light Rail at MSP Today
The Minneapolis-St. Paul Metropolitan Airports C...
Fast Facts
The HNTB Design Team Tunnel Characteristics:
Completion Date:
TUNNELS FACTS
+ Two side-by-side tunnels, each 1....
2001 2002
Minneapolis-St. Paul International Airport Light Rail Tunnel & Station Project Timeline
2003 2004
August 21, 200...
Fact Sheet
Category and code
Custom Solutions — ZZ
Primary use of structure
Light rail transit passage
Number and dimensio...
1 INTRODUCTION
MSP is the nation's eighth busiest airport per
number of passengers. The Minneapolis-St.
Paul Metropolitan ...
• A skyway connector linking concourses
C and G, parking, auto rental and the
transit center
In the late 1990s, the first ...
At this stage, the entire line being proposed
was to be constructed using a design/build
contract model.
2.1 Design and Co...
The design team worked to further define
the MAC’s design expectations and criteria
for the LRT project. These included:
•...
way 12R-30L) and comes up to street level
adjacent to 34th Street and the new HHH
Terminal. Associated open cut and cut-an...
nue South and the Fort Snelling Military
Reservation, alluvial deposits break the
limestone formation. The width of this
b...
3.4 Vertical Alignment
The vertical alignment is mainly a function
of the required at-grade elevations, the un-
derground ...
uniform, white, friable, and contains more
than 98 percent silica. Closely spaced weak
bedding and cross bedding planes ca...
a gasketed segmental lining offers the best
combination of lower risk and quality con-
struction required by the MAC desig...
and construction of the portion of the con-
nection structure required to be constructed
with cut-and-cover construction m...
In the buried areas where the TBM would
progress under operating area within the air-
ports, like aprons or taxiways, a pl...
REFERENCES
• Minnesota Department of Transporta-
tion. Hiawatha Corridor Light Rail Tran-
sit Preliminary Engineering Subm...
;X
DNR Asset Preservation
$4 Million Bonding Request
Infrastructure: Roads & Sewer
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RV 2014: Mobile Workshop #15- Integrating Transit into Large Institutions

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Monday, September 22, 1:15 pm–5:15 pm

Large institutions draw workers, customers and visitors: the MSP Airport, VA Hospital and Federal Government Center; Fort Snelling National Historic Site and State Park; the State Air Guard, Army Reserve and Air Force Reserve Centers; and the Mall of America. Travel the METRO Blue Line to see how these institutions met unique engineering challenges and incorporated LRT into their facility sites, operations and the very fabric of their organizations. Hear from the DNR, Metropolitan Airport Commission, VA hospital and city staff

Published in: Government & Nonprofit
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RV 2014: Mobile Workshop #15- Integrating Transit into Large Institutions

  1. 1. Project Overview Project History Project Overview Light Rail at MSP Today The Minneapolis-St. Paul Metropolitan Airports Commission (MAC) has been implementing a $3 billion Minneapolis-St. Paul International Airport (MSP) airport expansion plan at the nation's eighth busiest airport since 1996. In the late 1990s, the first LRT system to be developed in the state of Minnesota was being planned by the Minnesota Department of Transportation (Mn/DOT). Its completion links three of the region’s most popular destinations: Downtown Minneapolis, MSP and the Mall of America, with high-quality and efficient LRT service. However, to make the crucial link to the airport MAC had to look underground for solutions. The MSP LRT Tunnel and Lindbergh Station project consists of approximately 7,400 feet of twin bored tunnel boring machine (TBM) single-pass mined construction and mined cavern LRT station construction and 920 feet of cut-and-cover tunnel sections at the north and south tunnel approaches. The alignment begins to the north of MSP at the Fort Snelling Military Reservation, where the LRT tracks run underground, passing under the North Parallel Runway (Runway 12L-30R), Concourse C, and the Lindbergh Terminal's inbound roadway, and connects to the LRT station beneath the parking toll plaza. The system continues underground from the underground station, passing under the Lindbergh Terminal's outbound roadway, Concourse G, and South Parallel Runway (Runway 12R-30L), and comes up to street level adjacent to 34th Street and the new Hubert H. Humphrey Terminal. The LRT platform at the Lindbergh Station is approximately 65 feet below the level of the below grade Transit Center. A series of escalators, stairs and elevators are used to move passengers up from the LRT platform to the automatic people mover Transit Center levels and the concourse connector. Ancillary spaces for mechanical and electrical operation of the LRT system are located at the north and south ends of the platform. The opening of the Lindberg Station today connects directly to the Hiawatha LRT line providing high quality transportation access to the airport and key Twin Cities economic centers. As Minnesota's gateway to the world, the success of the Hiawatha LRT line is enhanced by the MSP LRT tunnel and Lindbergh Station project, and the seamless collaboration between MAC, the Minnesota Department of Transportation, MetCouncil, Metro Transit and the engineering and design consultants responsible for its successful delivery.
  2. 2. Fast Facts The HNTB Design Team Tunnel Characteristics: Completion Date: TUNNELS FACTS + Two side-by-side tunnels, each 1.8 miles long (longest! American Engineering and Testing in Minnesota)(Geotechnical Exploration) + Bored tunnel 1.4 miles long ! Charles Nelson and Associates + 920 feet of cut-and-cover sections at the north (Geotechnical Engineering) and south approaches + Tunnel 65-70 feet below surface! Hatch Mott MacDonald + Herrenknecht 250-foot-long, 500 ton Earth Pressure(Bored Tunnels and Tunnel Ventilation) Balanced Tunnel Boring Machine utilizing a pre-cast ! Hammel Green & Abrahamson (Architecture) bolted lining, with a 21-foot bore diameter + Each push by the borer excavates about 100 tons of earth to! Liesch and Associates (Environmental Compliance) advance 5 feet. The Tunnel Boring Machine (TBM) advances ! LTK Engineering Services (Light Rail Transit Systems) on average 80-100 feet per day. + Tunnel precast lining system begins manufacturing. From September 2001 through September 2002, more than 21,000 precast tunnel segments are manufactured. More than 873,900 + Tunnels: August 2004 square feet of precast concrete line the twin tunnels. + Prominently featured in major trade publications, including+ Light rail transit stations: December 2004 Engineering News-Record, Tunnel Business Magazine and Tunnels and Tunneling. + Innovative light rail tunnel precast tunnel lining systems wins the coveted Henry H. Edwards Industry Advancement AwardHole-Through Dates: by the Precast/Prestressed Concrete Institute (HNTB in + Southbound Tunnel: April 25, 2002 conjunction with County Materials Corporation) + Each tunnel is capable of supporting future wide-bodied+ Northbound Tunnel: October 29, 2002 aircraft, weighing up to 650 tons
  3. 3. 2001 2002 Minneapolis-St. Paul International Airport Light Rail Tunnel & Station Project Timeline 2003 2004 August 21, 2001 Tunnel boring machine makes trip from Duluth to the Minneapolis-St. Paul International Airport. September 2001 Tunnel precast lining system begins manufacturing. From September 2001 through September 2002, more than 21,000 precast tunnel segments are manufactured. November 2001 First bore on Southbound tunnel begins. June 2002 TBM moved from one site to opposite to start the Northbound tunnel. April 2002 Southbound tunnel TBM hole-through (4/29/02) July 2002 First bore on the Northbound tunnel begins. August 2002 Cover story of national tunneling trade publication Tunnel Business Magazine. October 2002 Northbound tunnel TBM hole-through (10/29/02), signifying the completion of the tunneling process. More than 873,900 square feet of precast concrete line the twin tunnels. November 2002 TBM disassembled, prepared for shipping overseas. December 2002 Crossover connection between the Lindbergh Station and tunnels is made. November 2002 Cover story of national engineering and construction trade publication Engineering News-Record. December 4, 2004 Grand opening! Last segment of the Hiawatha light rail transit line is officially open. November 2004 Signage and wayfinding system installed, final station clean-up complete. July 2004 Final electrical installed, lighting complete. April 2004 Decorative ceiling panels installed. Designed to mirror the shape of an airplane wing. August 17, 2001 Tunnel boring machine (TBM) arrives at port in Duluth from Holland. October 2003 Innovative light rail tunnel precast tunnel lining systems wins the coveted Henry H. Edwards Industry Advancement Award by the Precast/Prestressed Concrete Institute (HNTB in conjunction with County Materials Corporation) January 2003 Precast Lindbergh Station wall placement begins. September 2003 Station platform begins construction. October 2003 Rail connection to the Hiawatha line begins at the airport. February 2004 Station rail connection to the Lindbergh Station is made.
  4. 4. Fact Sheet Category and code Custom Solutions — ZZ Primary use of structure Light rail transit passage Number and dimensions of pre- cast concrete components Precast tunnel lining system: Southbound tunnel: 1,474 rings (10,318 segments) Northbound tunnel: 1,480 rings (10,360 segments) Total: 2,954 rings (20,678 segments) Approximate dimensions of rings: u Outside diameter of completed ring is 20'-6" u Inside diameter of completed ring is 18'-10" u Average width of the segment is 5'-0" u Thickness of the segment is 10" One ring is composed of: u Four standard segments each being 60° of total 360° ring u One counter key segment that is 60° of total 360° ring u One counter key segment that is 45° of total 360° ring u One key segment that is 15° of total 360° ring Multiple rings form the desired tunnel length using types of rings: u Type RS or Right Straight u Type RT or Right Taper u Type LS or Left Straight u Type LT or Left Taper Size and total square footage Southbound tunnel: 7,370 lf (436,060 sf) Northbound tunnel: 7,400 lf (437,840 sf) Total:14,770 lf (873,900 sf) Structural system used Precast concrete tunnel lining system Detailed project cost data Precast concrete tunnel lining system: $19,523,880 Total project cost:$109,890,000 Project timeline from design to occupancy Design: Fall 1999 to Summer 2000 Contract Award/NTP: January 19, 2001 Completion of TBM tunnels with precast concrete tunnel lining system:October 2002 Fact SheetPrecast/Prestressed Concrete Institute Award
  5. 5. 1 INTRODUCTION MSP is the nation's eighth busiest airport per number of passengers. The Minneapolis-St. Paul Metropolitan Airports Commission (MAC) owns and operates MSP and six reliever airports throughout the Twin Cities metropolitan area. The MSP facility accommodates more than 30 million passengers annually as a major hub for the airport's largest tenant, Northwest Airlines. Since 1996, The MAC has been implementing a $3.5 billion MSP 2010 airport expansion plan. This expansion project includes: • An expanded parking facility and new inbound roadways at the airport's Lindbergh Terminal • A new transit center, providing access to mass transit buses, proposed light rail and shuttles to off-airport rental facilities • A new airport runway and reconfigured taxiways • A new, ten gate Hubert H. Humphrey (HHH) Terminal • A new Automated People Mover (APM) system at the Lindbergh Terminal between the transit center, parking facility and the terminal, and a separate APM linking the main terminal with the new concourse and regional terminal Tunneling Under an Airport – The MSP Light Rail Transit Tunnel and Station Project Brian T. Hamilton, P.G. MSP LRT Deputy Program Manager and Project Office Engineer HNTB Corporation, Minneapolis, Minnesota, USA ABSTRACT: A new light rail transit (LRT) tunnel and station is being constructed under the Minneapolis-St. Paul International Airport's (MSP) main terminal and two main parallel run- ways. Constructing a LRT tunnel under the heart of one of the nation’s busiest airports presented new dimensions to project risk beyond controlling project cost and achieving construction schedule goals. With the economic consequences of any disruption to airport operations being unthinkable, ground disturbances and movements below runways and disruption of the airports landside and airside operations needed to be minimized. In this paper, the design and the construction management teams present a discussion of the de- sign methodologies and risk management strategies that were used to control costs, minimize project delays and minimize impacts to airport operations at the surface. This paper will be of interest to owners and engineers planning underground projects, especially those that present unique risks during construction.
  6. 6. • A skyway connector linking concourses C and G, parking, auto rental and the transit center In the late 1990s, the first LRT system to be developed in the State of Minnesota – the Hiawatha Transit Line – was being planned by the Minnesota Department of Transportation (Mn/DOT). Upon completion, the 11.6-mile light rail line would link three of the region's most popular destinations, Downtown Minneapolis' Nicollet Shopping Mall, MSP, and the Mall of America. Revenue service from Downtown Minneapolis' Nicollet Mall to Fort Snelling would begin in late 2003 and service to the airport and the Mall of America would follow by December 2004. In 2002 dollars, the overall cost of the Hiawatha Transit Line is $675.4 million. 2 PRELIMINARY ENGINEERING The airport portion of the Hiawatha Transit Line includes a tunnel underneath the heart of MSP, as shown on Figure 1. In the preliminary engineering stage, the tunnel ran underground starting at the north side of the airport, from the Fort Snelling site in Minnesota Air National Guard property, under Runway 12L-30R, under the Lindbergh Terminal's parking revenue plaza adjacent to a proposed transit center, under Runway 12R-30L, daylighting along East 70th Street, south of Signature Flight Support. LRT trains would stop at two stations on the airport campus. One located 70 feet below the Lindbergh Terminal and another at the airport's south side near a new HHH Terminal. When completed, LRT would serve as the primary transportation link between the two airport terminals (Minnesota Department of Transportation, 1999). Figure 1
  7. 7. At this stage, the entire line being proposed was to be constructed using a design/build contract model. 2.1 Design and Construction Planning at the Airport In the fall of 1998, the MAC formed a preliminary design and engineering team to investigate the proposed Hiawatha LRT Tunnel and Stations at MSP. The team, led by HNTB Corporation, includes Hammel Green and Abrahamson, Inc. (architects of the Lindbergh Station), CNA Consulting Engineers (mining and geotechnical engineering), and Hatch Mott MacDonald (tunneling and ventilation). The MAC team investigated the design requirements for an underground Lindbergh Terminal station that would connect to the APM level and Transit Center at the east end of the new parking decks. The airport's initial interest was to preserve ground surface areas and identify zones for cut-and-cover construction for future LRT ventilation and exit shafts, as well as a future stair and escalator connection for public access from the station platform to the APM and Transit Center levels above. Based on the team's preliminary finding, the MAC created “placeholders” for the shafts and a future Transit Center connection. Ar- eas were identified and reserved at ground level around the Lindbergh Terminal's Revenue Plaza, Transit Center and the out- bound roadways to be maintained “utility free” to preserve space for future shaft and cut and cover construction. The MAC team also organized a series of preliminary coor- dination meetings with the Mn/DOT design team and the Hiawatha Project Office (HPO), to discuss tunneling techniques, con- struction phasing and access restriction on MAC property. These discussions identified a number of conceptual issues of special concern to the MAC. Those issues included: • MAC Lindbergh Terminal Station’s identity and finish quality • Limited ground level spaces for cut and cover construction along East 70 Street and the Lindbergh Terminal • Limited construction access and phasing opportunities due to adjacent MAC air- port development projects and roadway completion schedules • Concerns for utility relocation costs and restricted access on the East 70th Street LRT right-of-way due to concerns over impacts to airport tenants and FAA Part 77 airfield safety clearance restrictions • Restricted automobile access posed by at-grade LRT crossings surrounding the new HHH Terminal • Construction risks of disruption to air- port operations from geologic features below the airport's South Parallel Run- way (Runway 12R-30L) These issues were discussed in detail be- tween the MAC and the HPO throughout spring and summer of 1999. In the late summer of 1999, the MAC authorized the formal creation of a MAC design team. The MAC design team prepared a cost up- date and review of the HPO’s preliminary engineering documents. The team also held series of bi-weekly work sessions starting in the fall to explore alternative design and en- gineering solutions that addressed MAC’s concerns. Two alternative delivery methods were examined and compared for the MAC’s evaluation. Those included a de- sign/build scenario where the MAC design team would prepare design/build documents to be incorporated in the overall HPO de- sign/build project. A second alternative looked at a more traditional design/bid/build scenario where complete documents were prepared and bid separately by the MAC. The options were compared in detail for schedule implication, risk assessment, cost effectiveness, and MAC design control.
  8. 8. The design team worked to further define the MAC’s design expectations and criteria for the LRT project. These included: • Near zero subsidence under active taxi- ways and runways • Restricted site and construction access at the Lindbergh Terminal area, due to sev- eral years of ongoing construction and recently completed landside projects • Roadway and access complications at the HHH Terminal on East 70th Street and 34th Avenue The underlying goal of the MAC was to produce a cost-effective LRT route and sta- tions through the MAC property to serve the travelling public in a safe, high quality envi- ronment corresponding with other MAC terminal facilities. The MAC's senior staff also outlined a number of specific goals in- cluding: • Developing a cost-effective design and engineering solution that is consistent with the funds allocated by HPO for the project • Working collaboratively and construc- tively with the HPO team to develop a solution that best serves the needs of the travelling public and respects the MAC’s operational and safety standards • Creating a signature station at the Lind- bergh Terminal with an identity and quality level that is appropriate to and commensurate with adjacent MAC ter- minal facilities • Minimizing airside and landside disrup- tion to the MAC during the LRT tunnel and station construction • Creating performance and engineering standards and documents that guarantee to minimize disruption to MAC airside operations that could result from ground subsidence due to underground tunneling • Identifying early construction needs for surface shafts in order to minimize fu- ture disruption or reconstruction of re- cently completed projects • Identifying clear, obvious circulation paths that enhances traveler wayfinding between the proposed LRT station and other terminal facilities • Minimizing long-term impacts to 34th Avenue South and East 70th Street In early winter of 1999, MAC authorized the design team to proceed with the de- sign/bid/build delivery model. Bids were opened for the MSP LRT Tunnel and Sta- tion project just 10 months later in August 2000. Excavation of the Hiawatha LRT Tunnel began in October 2001 by a joint venture between Obayashi Corporation and Johnson Brothers Corporation. Construction of the rail line and the Lindbergh and HHH Stations is expected to continue until the fall of 2004. 3 PROJECT DESCRIPTION In its final design format, the MSP LRT Tunnel and Station project consists of ap- proximately 8,100 feet of cut-and-cover, twin TBM or single mined tunnel construc- tion with a single mined station shown on Figure 2. The project consists of approxi- mately 7,400 feet of twin TBM or single mined tunnel construction and mined station construction. The alignment begins to the north of the MSP at the Fort Snelling Mili- tary Reservation, where the LRT tracks run underground, passing under the North Par- allel Runway (Runway 12L-30R), Con- course C, and the Lindbergh Terminal’s in- bound roadway, where it connects to the LRT station beneath the parking toll plaza. The system continues underground from the underground station, passing under the Lindbergh Terminal’s outbound roadway, Concourse G, South Parallel Runway (Run-
  9. 9. way 12R-30L) and comes up to street level adjacent to 34th Street and the new HHH Terminal. Associated open cut and cut-and- cover construction will be completed at ei- ther end of the tunnel. The LRT platform at the Lindbergh Station will be a below grade facility, approximately 65 feet below the level of the below grade Transit Center. A series of escalators, stairs, and elevators will be used to move passen- gers up from the LRT platform to the APM, Transit Center levels and the concourse con- nector. Ancillary spaces for mechanical and electrical operation of the LRT system are distributed at the two ends of the platform. The LRT platform at the HHH Terminal will be an open at-grade facility. The LRT route near the terminal will be associated with the planned parking facility serving the termi- nal. The project includes construction of a twin barrel tunnel, sections of cut-and-cover tun- nel construction, open cut boat sections, and an underground cavern rapid transit station (Lindbergh Station) on or immediately adja- cent to MSP property. Construction of the tunnel shall be by one of the two methods of construction as identified in the contract documents. Alternative 1 is construction of the tunnels using only a tunnel boring ma- chine the entire length of the tunnels and Alternative 2 is the construction of the tun- nels south of Lindbergh Station using a tun- nel boring machine and mining the tunnel segment north of Lindbergh Station using conventional mining equipment. 3.1 Alignment Selection Process The horizontal and vertical geometry of the tunnel is based upon the Hiawatha Corridor Light Rail Transit Design Criteria prepared by the HPO (Minnesota Department of Transportation, 1999). The track plan and profile from the preliminary engineering submittal formed the basis for further study and refinement as design controls became more defined. Numerous alignment alterna- tives were developed with the MAC's con- cerns in mind. Those alignment alternatives were developed subject to certain horizontal and vertical controls and design criteria. Cost comparisons were also prepared for the various alignment alternatives and associ- ated construction configurations. Each alignment was ranked according to potential impact on airport operations, constructabil- ity concerns and estimated construction cost. 3.2 Horizontal Alignment The horizontal controls included: the pro- posed HHH Terminal buildings, the location and orientation of the HHH Terminal Sta- tion, the configuration of access and egress roadways at the HHH Terminal, the location of a proposed Signature Flight Support building just to the north of an existing han- gar on the northeast corner of the intersec- tion of East 70th Street and 34th Avenue South, the location of the buried alluvial valley, the location and orientation of Lind- bergh Station, and tunnel construction meth- ods. The MAC design team considered the geol- ogy at the airport to be one of the most im- portant controls on the horizontal alignment. The geology beneath the airport campus consists of a layer of limestone, over a thin shale layer over a deep layer of sandstone. Approximately halfway between 34th Ave- Figure 2 APM platform Skyway/Concourse connector LRT station
  10. 10. nue South and the Fort Snelling Military Reservation, alluvial deposits break the limestone formation. The width of this break increases from north to south. The team concluded that the length of the tunnel through the alluvial valley should be kept to a minimum. The tunnel alignment was moved to the north to minimize the tunnel boring within the buried alluvial valley. This plan would also have the advantage of eliminating the tunnel boring directly under the south parallel runway. The preliminary design submission also proposed that the transit line share the ex- isting corridor between East 70th Street and Post Road – a distance of approximately a half-mile. This work would require the complete reconstruction of East 70th Street. The resulting street layout would provide one lane in each direction and could not be widened in the future without the removal of two buildings occupied by Signature Flight Support. The MAC design team also identi- fied construction phase constraints related to construction phase violations of FAA Part 77 airfield clearance restrictions at the proj- ect's southern portal and impacts on the Fort Snelling National Cemetery just to the south. After reviewing the airfield clearance restrictions, the MAC team decided to limit open excavation to outside of these clear- ance limits. Other concerns were identified involving disruptions to Signature Flights Support’s operations during construction. The track alignment that eliminated any re- construction on East 70th Street was pro- posed that would allow funds designated for the roadway reconstruction to be spent solely on the transit line. This plan would also provide schedule benefits and eliminate detours and other disruptions to normal traf- fic flow. As a result of this decision, the alignment was moved off East 70th Street to the airfield to the north. The southern portal was also moved to the west to remove FAA Part 77 airfield clearance violations that would have required the closure of a major taxiway for the duration of construction ac- tivities. The tunnel would surface just to the west of 34th Avenue South. 3.3 Portal Locations The preferred portal locations were subject to FAA airfield clearance restrictions and airfield development plans and constructa- bility concerns. The south portal was lo- cated in a manner that would minimize dis- ruption of traffic on 34th Avenue South and East 70th Street during tunnel construction. The north portal was located at a point where cut-and-cover tunnel construction can be completed without violating the safety area as defined by the FAA. The MAC wanted to preserve the limestone cap with the FAA airfield safety areas of the runways and associated taxiways. These re- quirements would not allow excavation of limestone within 250-feet of the North Par- allel Runway and 507 feet south of the South Parallel Runway. Preservation of the limestone cap is required due to live load considerations. The construction must result in a surface capable of supporting Class V aircraft (Boeing 747 or equivalent size) within the safety areas. The FAA Part 77 airfield clearance restric- tions are intended to ensure an obstacle free volume of space surrounding the runways and taxiways. As such, the portal locations must respect these restrictions. The con- struction contractor would not be able to use equipment such as cranes without restric- tions within these limits. In most cases, any construction within the Runway Safety Area (RSA) would require a closure of the run- way or taxiway, and relaxation of the RSA by the FAA was not possible. These criteria suggests that the interface of the cut-and-cover tunnel and the mined/bored tunnel at the northern end of the alignment would need to be constructed no closer to the north parallel runway than 250-feet plus some buffer zone to allow for construction operations. At the south side, the cut-and-cover to retained cut interface would need to be no closer than 560 feet from the centerline of the South Parallel Runway (Runway 12R-30L).
  11. 11. 3.4 Vertical Alignment The vertical alignment is mainly a function of the required at-grade elevations, the un- derground elevation required at Lindbergh Station, the water table, the extent of the limestone formation near 34th Street South and the location of Runway 12L-30R at the north side of the airport. The vertical controls included: the elevation at the HHH Terminal Station, the elevation of 34th Avenue South, the horizontal extent and elevation at the bottom of the limestone formation just east of 34th Avenue South, the water table, the elevation at the northern limit of the airport property, FAA Part 77 airfield clearance restrictions, the tunnel construction method, and the creation of a low point in the tunnel just south of the Lindbergh Station platform – was consid- ered the optimal location to collect and re- move track bed drainage. 4 GEOLOGICAL CONDITIONS The majority of the tunnel will be con- structed in the St. Peter sandstone below the Platteville limestone. However, the align- ment crosses glacial soil filled buried valleys in three locations. The Twin Cities metropolitan area, includ- ing the area of direct interest to the LRT project, is underlain by nearly 1,000 feet of sedimentary rocks of early Paleozoic age. These gently dipping to near-horizontal rocks form the Twin Cities structural and hydrologic basin. A mantle of glacial and post-glacial deposits covers the area. In general, the overburden materials along the LRT alignment consist of fills, alluvial, or till materials. The stratigraphic section underlying the project area consists of approximately 1,000 feet of sandstone, shale, and carbonate rocks of Cambrian and Ordovician age. The youngest formation is the Platteville forma- tion, an approximately 30-foot thick forma- tion, which is divided into several dolomitic limestone and dolomite members. At the base of the Platteville limestone is the thin (2-feet to 5-feet thick) Glenwood shale that overlies the St. Peter sandstone. The St. Peter is a 150-foot thick massive sandstone unit composed of fine-grained to medium- grained, well-rounded and uniformly graded quartz sand. The majority of the LRT tunnel will be constructed in the St. Peter sandstone (Minnesota Geological Survey, 1972). In the Platteville limestone, steep to vertical joints is common at a typical spacing of 20 feet to 40 feet. Many are tight, allowing lit- tle water movement, whereas others transmit water readily. Open bedding planes in the limestone are water bearing. The uncon- fined compressive strength of unweathered rock in the Platteville formation typically ranges from 9,000 psi to 35,000 psi (Metro- politan Airports Commission, 2000). flake off when exposed by excavation. It does form a relatively impervious layer so that water in the overlying limestone is commonly perched above it. The uncon- fined compressive strength of Glenwood shale has been found to be as high as 7,200 psi in samples taken for the construction of the Minneapolis East Interceptor in Minnea- polis (Metropolitan Waste Control Commis- sion, 1985). However, considerably weaker shale occurs in layers in the formation. The St. Peter sandstone is low-strength quartz sandstone. Most of the formation is Glacial drift Platteville limestone Glenwood shale (2-3 ft.) St. Peter sandstone > 60 ft.
  12. 12. uniform, white, friable, and contains more than 98 percent silica. Closely spaced weak bedding and cross bedding planes can result in very weak sandstone. Irregularly spaced, steeply dipping (more than 70 degrees) joints are present in the sandstone. Water moving along a joint can erode the friable sandstone, and, where the loosened sand can migrate, voids may develop. Voids have been known to form near or next to lined tunnels and within hundreds of feet of river bluffs and buried valleys. The unconfined compressive strength of the St. Peter sand- stone typically ranges from 0 psi to 500 psi. However, nodules or concretions have been found with compressive strengths as high as 14,600 psi (Metropolitan Waste Control Commission, 1985). These nodules are scattered, but can create problems during hydraulic mining and hand excavation and can damage cutter teeth on tunnel excava- tion machines and road headers. Nodule sizes range from a few cubic inches to sev- eral cubic feet. As shown in Figure 3, the tunnel alignment lies in buried valleys in three areas. In these areas, glacial soils now exist in areas previ- ously occupied by bedrock. 5 CONSTRUCTION CONSIDERATIONS 5.1 Geological Impacts on Tunneling Methods The MSP LRT project has a unique geologic setting in that the ground conditions along the tunnel length comprise a limestone cap, underlain by soft sandstone with unusual properties above the water table, both inter- sected by buried valley containing glacial deposits below the water table. Above the buried valley lie taxiways, utilities and structures for MSP, which require protection during tunneling works, to avoid disruption to airport operations due to ground move- ments. Traditionally, in the Minneapolis area, the sandstone would be excavated eas- ily beneath the limestone cap with a minimal need for support and final lining. However, the presence of the buried valley and the need to protect the operations of the airport dictate that special measures be applied to successfully construct the tunnel in that sec- tion. There are various construction methods available to achieve the MAC's objectives. The option of using a closed face TBM with gasketed segmental lining with the TBM driven in EPB mode was selected by the de- sign team. This method was chosen because it provides continuous face support and ground support, hence lower risk. A closed face TBM more easily copes with boulders. The EPB option was chosen despite a higher initial cost, skilled workforce requirements and intensive mechanical/electrical support requirements. In general, the tunneling methods that did not provide continuous face support in com- bination with a watertight lining, were con- sidered higher risk in terms of potential dis- ruption to the airport operations. Many of the construction methods do not provide ef- fective control over ground movements. The selection of a closed face TBM utilizing Figure 3 Buried valley
  13. 13. a gasketed segmental lining offers the best combination of lower risk and quality con- struction required by the MAC design ob- jectives. 5.2 Tunnel Construction Alternatives Construction of the tunnel will be accom- plished by one of the two methods. Alter- native 1 is construction of the tunnels using only a tunnel boring machine the entire length of the tunnels and Alternative 2 is the construction of the tunnels south of Lind- bergh Station using a tunnel boring machine and mining the tunnel segment north of Lindbergh Station using conventional min- ing equipment. The prospective bidders had to identify their choice at the time of bid- ding. The mined tunnel option consists of a single tunnel bore containing both the northbound and southbound tracks. This option occurs between the north end of the Lindbergh Sta- tion and the start of the North Portal cut-and cover-tunnel. Similar construction methods have been used in the Twin Cities for under- ground space development and sanitary sewer meter chambers. The mined tunnel option requires excavation of greater sandstone volumes than the TBM option. This option is economically viable because of the low unit excavation costs achievable with large excavation equipment. A contractor that chooses the mined tunnel option will use large loaders and backhoes for excavation, trucks for haulage, and a large backhoe mounted roadheader for lime- stone roof and sandstone wall trimming. Much of the tunnel may be excavated in one pass. Near the station, where the profile is deeper, the contractor may need to excavate using a top heading, followed a short dis- tance back by bench excavation. Wall panel installation will be done later with minimum impact on more critical activities. 5.3 Lindbergh Station The MAC's primary objectives for the de- velopment of the Lindbergh Terminal Sta- tion was to create a signature station with an identity and quality that is commensurate with adjacent MAC terminal facilities. They wanted to identify clear and obvious circu- lation paths that enhances traveler wayfind- ing between the proposed LRT station and other terminal facilities. The Lindbergh Terminal construction would need to be ac- complished in a manner that minimizes dis- ruption to the airport operations during the construction phase. Areas around the Lindbergh Terminal had been under construction continuously since the MSP 2010 airport development program started in 1996. Most of this construction work was due to be completed about the same time that the LRT construction would be starting. The MAC team decided that it was not desirable to disturb these new fa- cilities just as their construction was being completed or to subject the traveling public to several additional years of construction. Mn/DOT's concept would have required extensive cut and cover construction opera- tions with the transit plaza area. The MAC's concept of a mined station would minimize the cut-and-cover operations. A mined sta- tion would mitigate concerns that relate to economics, utility relocation, space alloca- tion and schedule. Due to the schedule constrains, the MAC decided to move forward with the design Future Lindbergh LRT Station
  14. 14. and construction of the portion of the con- nection structure required to be constructed with cut-and-cover construction methods. This construction would be accomplished coincident with the Transit Center construc- tion in the spring and summer of 2000. The MAC team also modified the Lindbergh Station design from a binocular station con- figuration with a 300-foot-long platform to a monocular station with a platform length of 280 feet. A monocular station arrangement would further achieve the MAC's objective of creating a signature architectural station, while a shorter platform length would enable the project to reap a substantial cost savings. A 280-foot platform would still be able to accommodate three car trains. The mo- nocular arrangement also resolved space al- location concerns over the space dedicated for mechanical/electrical equipment. The platform length would still be able accom- modate three 94-foot-long rail cars. The Lindbergh Station will be constructed within a mined cavern in sandstone below a layer of limestone below the airport parking toll plaza. The 60- by 30- by 500-foot-long cavern will be lined with precast wall and ceiling panels. The middle 280 feet of the cavern will be a two-story high public plat- form area. Each end of the cavern will in- clude two levels of ancillary spaces for me- chanical and electrical systems. The cavern floor will consist of slabs-on-grade for a passenger platform and track support struc- ture. A signal and communications vault and a sump pump room are located below the platform level slab. Airshaft structures with emergency exit stairs extend vertically from each of the ancillary spaces to the sur- face. Within the platform area and between tracks, escalators, an elevator and stairs con- nect the platform with a mezzanine level. The mezzanine spans the tracks to connect to an upper level tunnel leading to the base- ment of the Transit Center building. The connection to the Transit Center building will be constructed by excavating from the surface and covering the excavation with a structure to support the grade level. 5.4 Settlement Control Given the economic consequences of any disruption to airport operations, ground set- tlement controls and mitigation demands special attention. To minimize settlement risk on airside operations, candidate tunnel alignments under consideration that pre- served limestone cap within the safety area of the runways and their associated taxiways were favored. Minimum turning radii along tunnel alignments were maintained at no less than 1,000 feet. The MAC team specified the continuous use of pressure balanced TBM buried valley ar- eas for the project. The correct use of a closed face TBM would provide an effective means of controlling the short-term immedi- ate settlement due to tunneling. The contin- ual operation of the TBM in closed mode maintaining enough face pressure, to mini- mize ground movements and water inflows at the tunnel face was considered important to settlement control. Procedures are being utilized to monitor ground movements, interpret the results, and identify trends in a prompt manner as the TBM progresses under key areas. This en- ables adjustments to be made to the operat- ing parameters of the TBM or any planned mitigation measures to be implemented early, before potential problems and serious implications develop. Technical specifica- tions also established trigger values and set- tlement limits for the various structures un- der which the tunnel pass. Southbound Tunnel Moveable Work Zone over buried valley
  15. 15. In the buried areas where the TBM would progress under operating area within the air- ports, like aprons or taxiways, a plan was developed to keep aircraft out of the area. In some cases, aircraft gates would need be closed to aircraft. Impact to airport opera- tions is being kept to a minimum through the use of moving work zones where the area closed progresses along with the mining op- erations. 6 VALUE ENGINEERING AND RISK EVALUATION The move to make the tunnel construction under airport control was despite the Hiawatha Light Rail Transit's ambitious cost and schedule objectives. A difficult political situation in Minnesota led to the promise that the Hiawatha LRT system would have to be constructed within budget and the system would need to be operational by the end of December 2004. Hiawatha LRT offi- cials set the maximum budget of the MSP LRT Tunnel and Station early in this pre- liminary design stage to $117 million dollars and set the award date / notice-to-proceed date of the contract to September 18, 2000. That meant that the bid opening for a tunnel contract would need to be no later than August 2000. In this working environment, every design decision was made with cost, schedule and risk impacts in mind. Value engineering studies and cost comparisons of alternatives were made at each stage of the project. These studies included reviews of alignment alternatives, evaluating underground space needs and civil design concepts. Vertical alignment alternatives compared varying grades (4 or 5 percent grades) were used. A review of horizontal alignment alternatives identified a need to move the alignment off East 70th Street to save the costs of recon- structing the street. Another study identified an opportunity to reduce the length of the Lindbergh Station by 20 feet. Risk evaluations identified a need to move a portion of the horizontal alignment to the north to keep the tunneling activities within a buried alluvial valley away from under- neath runways and also led to the selection of the specified tunneling methods and set- tlement reduction measures. 7 CONCLUSION The Hiawatha Transit Line is the first LRT system to be developed in the State of Minnesota. The 11.6-mile light rail line would link three of the regions most popular destinations, Downtown Minneapolis's Nicollet Shopping Mall, the MSP, and the Mall of America. An integral portion of this effort is the construction of a 1.8-mile tunnel underneath the MSP, the nation's eighth busiest airport, and adjacent to an ambitious $3.5 billion dollar airport expansion project. The project is located in a crowded, unforgiving airport environment. The construction is being subjected to challenging ground conditions, stringent performance criteria, a tight construction schedule and budget, and close public scrutiny. This project is requiring a concentrated effort from the MAC the HPO, the consultants and responsible contractors to ensure the successful completion of the work and its completion by the mandated deadlines and funding limits.
  16. 16. REFERENCES • Minnesota Department of Transporta- tion. Hiawatha Corridor Light Rail Tran- sit Preliminary Engineering Submittal. 1999. • Minnesota Airports Commission, MSP LRT Tunnel and Station Project Geo- technical Design Report (prepared by CNA Consulting Engineers). 2000. • Metropolitan Waste Control Commis- sion. Contract Documents for the Min- neapolis East Interceptor, Volumes 4a and 4b - Geotechnical Report. 1985 • Minnesota Geological Survey, P.K. Sims and G. B. Morey, eds. Geology of Min- nesota: A Centennial Volume. 1972
  17. 17. ;X DNR Asset Preservation $4 Million Bonding Request Infrastructure: Roads & Sewer ?A@55 ?A@5 ?A@55 ?A@62 ?A@5 GV204 GV204 Fort Snelling Station ST205 METROBlueLine WEIGEL BLVD 88THDIVISIONRD CONSTITUTION AVE SLOAN BLVD XFEDER A L DR R OED ER CIR BLOOM ING TO N RD MINNEHAHA AVE TOWER AVE M IN NEHAHA AVE M INNEHAHA AVE FEDERAL DR TAYLO R AVE M INNEHAHA AVE MINNEHAHA AVE FORT SNELLINGDR MINNEHAHA AVE BLO OM INGTON RD COLVILLE AVE Upper Mississippi Academy Building (Temporary) Minneapolis Park and Recreation Board 9 Hole Golf Course and Fields (Lease from DNR) LRT Park-and-Ride Lot BSA Northern Star Council Base Camp LRT Park-and-Ride Lot Fred Wells Tennis and Education Center Minneapolis Park and Recreation Board Coldwater Spring 101 102 103 55 65 67 Fort Snelling Upper Post Hennepin County Public Works Ramsey Dakota BLOOMINGTON MINNEAPOLIS RICHFIELD MSP INTL. AIRPORT FT. SNELLING TERR. Produced by Hennepin County Housing, Community Works & Transit Existing conditions and future opportunities Fort Snelling Upper Post Publication date: 5/6/2014 This map has been created for informational purposes only and is not considered a legally recorded map or document. Hennepin County makes no warranty, representation, or guarantee as to the content, accuracy, timeliness, or completeness of any of the information provided herein. About this map National historic designation combined with its location within unincorporated Hennepin County and complex jurisdictional authorities have hampered redevelopment opportunities for Fort Snelling Upper Post. The nearby Fort Snelling LRT station has great potential to support current recreational and future housing, educational and redevelopment uses. Hennepin County and the National Parks Service, Veterans Affairs, MN Dept. of Natural Resources, MN Historical Society, and Minneapolis Park and Recreation Board in 2012 formed the Joint Powers Agreement that clarifies the roles and responsibilities of the partners and lays the groundwork for future investment. This map captures the wide range of activities that already animate the Fort Snelling Upper Post area and indicates some of the redevelopment opportunities just over the horizon. Building 55, 65, 67 State Bonding STS Homes Stabilization 2008 $500,000 2010 $1.2 Million Upper Mississippi Development Mortenson Development and Construction Upper Mississippi Academy Charter School Bishop Henry Whipple GSA Building Restoration Veterans Affairs Homeless Veterans Housing Veterans Affairs Homeless Veterans Housing 58 Housing Units Minnesota Historical Society Building Restoration Visitor Services Enhancements Minneapolis-St.Paul International Airport MnDOT / 0 500 1,000 Feet Joint Powers Agreement Partnership Joint Powers Agreement Partnership

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