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

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. 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. 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. 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. 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. • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. ;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