Aggregate Pier Ground Improvement for Transportation Projects 2019 - - PowerPoint PPT Presentation

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Aggregate Pier Ground Improvement for Transportation Projects

2019 Midwest Geotechnical Conference

• W. Lyle Simonton, P.E.

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OVERVIEW

 Intro to Vibro Ground Improvement  Objectives of Aggregate Pier/Stone Column Ground Improvement  Examples of Transportation Projects (MO, IL, IN, OH, WI, OK, KS, soon to be CT)  Specific Lessons Learned with Ground Improvement Specifications/Install/Testing

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Vibro-Flot, Probe

Hydraulic Motor or

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Stratocaster Vibro Rigs

• 40,000 lbs. of Crowd Force
• 90,000 lb. Rig
• 1st of these type of rigs in the USA

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Excavator-Mount Mast System

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Crane-Suspended Vibro

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Basic Installation Techniques

 Dry Top Feed

• Stable, Cohesive Soils
• Pre-Drill or No Pre-Drill

(hole diam., obstructions)  Dry Bottom Feed

• Collapsible Conditions
• Stone Tremied to Bottom

 Wet Top Feed

• Sand / Silty Sand Below WT
• Liquefaction Mitigation (with

stone)

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Dry Top Feed Stone Columns (stable soil)

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Dry Bottom Feed Stone Columns (collapsible soil)

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I-69 Indiana Gohmann (GC) SR64 Over I-69 E.S Wagner (GC) ILDOT Cedar Lake Rd Round Springs, IL

Dry Bottom Feed Stone Columns

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Wet Top Feed Stone Columns (sand with fines)

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DOT Projects

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Objectives of Ground Improvement

 MSE Wall and Earth Embankment Support  Bearing Pressure – Range based on wall height (5ksf typ)  Settlement Criteria

• Soil parameters critical (CPT preferred)
• MSE wall supplier input
• Define when/how it’s measured
• May need to stage construction

 Liquefaction Mitigation

• Understand limitations of GI techniques
• Cannot substantially densify soils with fines >10%

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Objectives of Vibro Ground Improvement

 Reinforce Soft to Med. Stiff, Cohesive/Fine-Grained Soils

• Bearing pressure
• Settlement
• Not improving the soil strength
• Modulus test / monitor settlement

 Densify Granular Soils

• Bearing pressure
• Settlement
• Liquefaction mitigation
• Substantial improvement proved with SPT/CPT



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Design Considerations

 Primarily Bearing Pressure and Settlement  Global Stability  Liquefaction Mitigation  Who Does the Design?  Verification Program

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Specification / Special Provision

 Missouri DOT – Aggregate Column Ground Improvement  Experience – Work and Site Superintendent  Aggregate Columns

• Vibratory Compacted
• Tamper Compacted

 Verification Program  Plans indicate bearing pressure, settlement, global stability, etc.

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Verification Program

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 New Interstate From Indianapolis to Evansville  Current Design Build Work - 4 Sections

• Section 1 – 13 miles – 5 Contracts
• Section 2 – 29 miles – 7 Contracts
• Section 3- 25 miles – 7 Contracts
• Section 4 – 27 miles – 2 Contracts to Date

 Subsurface Constructors Work

• Work on 4 - 5 Contracts (with 4 GCs)
• Vibro Stone Columns
• Wick Drains

New I-69 Design Build Indiana DOT

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Design-Build Project Approach

 State’s Geotechnical Engineer Makes General Recommendations  Design-Build Team Develops Concepts

• Exclusive Agreement with Specialty Contractor
• Confidential Agreement with Specialty Contractor,

But Not Exclusive  Winning Team Develops Design

• May Take Additional Geotech Info
• Original Assumptions May Change
• Put Ground Improvement Portion Out For Bid

To Specialty Contractors

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Section 3, Segments 12,13

 Fred Weber / Jacobs Engineering  I-69 Over CR900E

• New Approach/Bridge Over Road
• Significant Fill Height of Approach
• Approach Embankment (Wick Drains)

 Twin Bridges Over Weaver/Vertrees Ditches

• No New Embankment / MSE Walls
• Bridge Abutment at Grade / Pile Foundations
• Liquefaction-Induced Settlement

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Twin Bridges Over Weaver/Vertrees Ditches

 Loose Sands, Sandy Loam To 10 ft to 18 ft  Existing SPT N = 0 to 4  Original Proposal Was Deep Dynamic Compaction  Additional Borings Taken, Team Decided on VSC  Required Post-Treatment SPT N = 8

• Minimize Earthquake Induced Settlement
• Designed VSCs = 30” diam, 15ft, 7ft spacing
• Diff. Settlement in Transition Zone (further spacing)
• Required 9-ft Spacing in Transition Zone

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Plans Sheets BENT 2 BENT 1 2.5’ diam. VSC @ 7’ OC, except last row

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N > 8 N > 8

Pre- and Post-Treatment SPT Tests Results Bent 1, Structure 33

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Pre- and Post-Treatment SPT Tests Results Bent 2, Structure 34

N > 8 N > 8

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I-69 Over CR 900E

 Twin Bridges 55-Ft Long With MSE Wall Abutments  MSE Wall Approx. 25-Ft High From Leveling Pad  Liquefaction Analysis – OK Under Fill  Global Slope Stability Requires Stone Columns

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I-69 Over CR 900E

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I-69 Over CR 900E

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I-69 Over CR 900E

Cross Section

Stone Columns Work Plan:

• Diam = 3 ft.
• Spacing = 8 to 9 ft.
• Depth = 37 to 41 ft.

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Lessons Learned

 Designing / Specifying Stone Columns What Is The Goal of Ground Improvement?  Specialty Contractor May or May Not Perform the Design  Specialty Contractor Should Be Consulted  Verification of Performance  Different Means and Methods to Construct

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MSE Walls for MRB Approach

 3 Large (up to 45ft) MSE Walls over I-70 in St. Louis  Bearing pressure = 3,500psf to 7,100 psf  Total Settlement = 2”  Global Slope Stability

• FS (undrained) = 1.2
• FS (drained) = 1.5

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MSE Walls for MRB Approach

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Transition Columns Moved MSE Wall Slope Stability Concern * Somes slides/pics complements of Dan Brown and Associates

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MSE Wall Pushed Out; Enter DBA. More Critical Global Stability Issue became Apparent

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Max Wall

• Elev. 497’
• r 47ft Tall

Bedrock Transition Columns Stone Columns MSE Strap Zone General X-Section when DBA Arrived

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Analysis of West MSE Wall

 Initially observed settlement of wall during construction (about 20ft of wall built)  Subsurface recommends staged construction in thirds (1/3 total height of wall)  Consultant analyzed global stability/soil strengths

• FS(undrained) = 0.9
• FS (drained) = 1.6

 Also observed some lateral movement of shorter wall where no stone columns installed

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Wall pushed out. Movement occurred during installation of transition columns and stopped upon completion.

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Questions?