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Geotechnical Aspects of theTwin Ports Interchange (TPI)
Duluth, Minnesota
Rich Lamb, P.E.
2019 Midwest Geotechnical Engineering Conference
September 16-19, Columbus, OH
mndot.gov
Sorry, Wisconsin
Project Location
Lake
Superior
Duluth,
Minnesota
Superior,
Wisconsin
Port of Duluth-Superior
1
3
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Current Interchange
• Known locally as the “Can of Worms”
• 3rd highest crash rate statewide for
interchanges
• 33 aging bridges (built in late ‘60’s),
mainline interstate on land bridge
• 16 bridges weight restricted 7 non-
redundant
• Problem for over-sized and over-weight
traffic coming from port and getting on
Interstate
4
Routes of Diverted OSOW Traffic
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Current Main Interchange
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I535
Lake Superior
Historic
Neighborhood
Trestle Bridges (mainline I35 and all ramps)
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US53
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Garfield Interchange I535
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Twin Ports Interchange (TPI) Project Goals
• Enhance safety by eliminating blind merges and
left exits
• Replace aging infrastructure
• Reduce maintenance and closures
• Reduce bridge structure
• Improve freight mobility
• Allow oversize/overweight freight on the Interstate
by reconstruct/rehab substandard bridges
10
Project Overview
• Alternate Deliver Method - Construction
Manager/General Contractor (CMGC)
• Currently nearing 60% design status
• Consultant design for both roadway and bridges
• Construction scheduled for 2020-2022 ($250-
300M)
• Driven Pile Load testing and Column Test
Project (Rigid Inclusions) currently underway
11
Construction Manager/General
Contractor (CMGC)
• Contractor hired at start of design under professional/technical consultant contract
• Contractor responsibilities
• Constructability Reviews
• Maintenance of Traffic, Construction Staging Reviews
• Work will be let in two Work Packages
• Three cost estimates (EE, Contractor, ICE) must be close for Contractor to do work
12
Current Design Layout
• 14 New Bridges, 4 Bridge Rehabs
• ~600,000 sq. ft. of Column
Supported Embankments
• Fill heights up to 38 ft.
• 40% reduction in bridge deck area
• 8,000 L.F. Retaining Walls
• Cast-in-Place Concrete Cantilever
• MSE
13
Geotechnical Design Team
• Subsurface Investigations, Ret Wall Geotechnical Reports, Roadway Soils
• Ground Improvement Design, Modeling
• Supplemental Subsurface Investigations
• Early work on TH 53 Embankments
• Lateral Pile Stability
mndot.gov/
Column Supported Embankment Design
• Designed by consultants (Barr
Engineering and Itasca Engineering)
• Most economical column is full
displacement grouted column
• Diameters 16-18 in.
• Column Spacing 8-10 ft.
• Rough Unit Cost ~ $40/sq. ft.
• Includes wall cost
15
Subsurface Investigations
• 120 Historic Borings from 1960’s (poorly located, ±50 ft.)
• 150 Cone Penetration Test (CPT) soundings
• 250 Modern SPT Foundation Borings
• Dozen or so Test Pits
16
General Subsurface Conditions
9/24/2019 mndot.gov 17
Main Intersection US 53 Garfield Interchange
Very Dense
Sand
>150 ft.
Bedrock
Dense Sand
Org Silty
Clay
Sand fill
Bedrock
Vert Dense
Sand/Silt
Clay
Stiff Silt and
Clay
Sand fill
Dense Sand
40-60 ft
100 ft.
150 ft.
10-55 ft.
thick
Clay
Var.
Soil Variability
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Soil Variability
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107 ft.
54 ft.41 ft.
Miller Creek Culvert InletBridge 69902 West Abut
35 ft.
Sloping Bedrock
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90 ft.
500 ft.
Bedrock
Miller/Coffee Creek Culvet
3D Soil Model
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High Ground Water Table
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Lake Superior
603.5 MSL
Existing Grade ~606
Lake Tides
• Strong North Wind = 1-2 “tide”
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Soil Contamination
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Soil Contamination
• Petroleum, lead, arsenic, PAH, Asbestos
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Big Geotechnical Challenges
• Avoiding any excavation to limit cost of treating
contaminated soil and groundwater
• Possible Steel Corrosion from contaminated soil
• Construction Staging does not allow for
embankment settlement wait periods
• High groundwater
• Urban fill
26
Bigger Geotechnical Challenges
• Interaction of CSE foundation elements with
bridge/wall driven piles
• Ground heave/lateral displacement from
“forest” of full displacement columns
• Low fill ground improvement
• Building bridge/walls/embankments over in-
place utilities
• Reviewing designs using finite difference
method
27
Low Embankments
• No excavation
• No settlement wait periods
• 1 inch of long term
allowable settlement
289/24/2019 mndot.gov 28
4-6 ft. fill
Weak Soils,
highly
contaminated
30-60 ft.
Dense Soils
Low Embankment Foundation Design
• Columns Supported Embankment
• Driven piles or grouted columns
• 10 ft. center spacing
• 1 ft. thick reinforced concrete LTP
299/24/2019 mndot.gov 29
LTP
Dense Soils
4-6 ft. fill
Interaction of CSE columns and bridge piles
30
Ground Heave/Lateral Displacement Problem
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Driven Piles
Full
Displacement
Columns
Column Test Project
• 63 CMC column 18 in. dia. 65 ft.
• Wick drains ½ area
• Driven 16 in. pipe pile
• Two Static Load Tests on columns
• Instruments
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Column Test Layout
33
Test Area Soils
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65 ft.
Column Test Embankment
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Instrumentation
• 63 total gages
• Piezometers
• Survey targets
• Extensometers
• ShapeAccelArray
• Vertical and horizontal
• Strain Gages
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Initial Instrumentation Results
37
Current Instrumentation Results
• Lateral Deflections ~4 inches near columns (3 ft), but only
½ inch 10 ft. away
• Heave – 1 inch
• Pore Pressures – dissipates quickly
38
Vertical SAA
39
If Ground Movement is Problem
• Use non-displacement columns or H pile
in “buffer zones”
9/24/2019 mndot.gov 40
Auger Cast
or H Pile
Full
Displacement
Columns
123
Sanitary Lift Station
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Cross Section
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Options
• Remove building
• Fill-in basement and drill
foundations through
floor
• Span over
45
Bridge Piling Adjustments
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Reviewing CSE Designs
• How to check 2d, 2.5d and 3d Finite Difference
Method models
47
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Column Supported Embankments 101
9/24/2019 mndot.gov 50
EmbankmentLoad Transfer
Platform
Weak Soils
Dense Soils
Rigid Inclusions
(columns/piles)(70-95% of
embankment load)
Rigid Inclusions (Columns or Piles)
• Full Displacement Grout Columns
• Non-displacement Grout Columns
• Driven piles
• H sections
• Pipe sections
• Typical Spacing 5-10 ft. centers
• Pile Caps typically used
9/24/2019 mndot.gov 51
$12-$20 / LF
$30-$40 / LF
52
CSE with misc Structures/Utilities
9/24/2019 mndot.gov 53
EmbankmentMSE Wall
CIP Wall
Storm Sewer
Exit 535 EB OH Sign
Light
Tower
Archaeological Concerns
• I-535 and Garfield Avenue
• Brown’s Trading Post
• North side of Piedmont Avenue
• Known Native Cemetery
• Some graves relocated in 1870 to Railyard
• Coffee Creek Banks
• Culvert built over stream and filled
• Beneath the structure
• Old Lakeshore
• Drilling in these areas suspended
54
9/24/2019 mndot.gov 55
Load Transfer Platform Design
• Acts as a pile cap – evenly distributes load to columns
• Select well graded granular fill (94-98% compaction) (MnDOT Class 5)
• Minimum of three horizontal biaxial geosynthetic reinforcement
layers with vertical spacing of 8-18 in.
• LTP thickness (½ the clear span between columns)
Full Displacement Columns
• “Drilled Displacement Piles”
• Very few spoils, low noise, vibration
• Reverse flight Augers push soils down and away from column
• May displace soils laterally – problem for adjacent structures
• Diameters of 12-24 inches, and typical lengths of 65-85 ft.
• Difficult to penetrate dense soil layers
9/24/2019 mndot.gov 56
Menard – Controlled Modulus Column
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Non Displacement Columns
• “Auger Cast Pile” or
“Continuous Flight Auger Pile”
• Diameters of 12-24 in.
• Depths of 100 ft. or more
• Low noise, vibration
• Spoils much greater than FDC
9/24/2019 mndot.gov 58
Displacement Piles
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Non-Displacement Piles
• “Pile Supported Embankment”
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Questions or Comments?
Geology
• What has shaped the subsurface conditions the project
site?
• Volcanoes (igneous bedrock)
• Glaciers (dense soils)
• Lake Sediments (organics and soft clay)
• Erosion from stream flow (variability)
• Land use (surface fill material, contaminants)
mndot.gov/
Subsurface Investigations
• 120 Historical Borings (1960s)
(bridges)
• 100 Modern Borings (AET)
(bridges)
• 150 Cone Penetration Test
(CPT) Soundings
(embankments)
• 150 Future holes
9/24/2019 mndot.gov 63
75-100’
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Tall Embankments
679/24/2019 mndot.gov 67
Embankment
20-40 ft.
Weak Soils
30-60 ft.
Dense Soils
Tall Embankments
689/24/2019 mndot.gov 68
Embankment
20-40 ft.
Weak Soils
30-60 ft.
Dense Soils
Typical Section I35 and Ramps
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Org Chart - CMGC
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Typical Section for CSE
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Typical Section for CSE
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Perched Abutments
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Weak Soils,
highly
contaminated
30-60 ft.
MSE Wall
Dense Soils
Main Interchange
75
US 53 Bridges
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Garfield Interchange
77
