Midwest Geotechnical Conference Columbus, Ohio September 2019 Bob - - PowerPoint PPT Presentation

Midwest Geotechnical Conference

Columbus, Ohio September 2019

Bob Arndorfer

• AASHTO Definitions:
• Cohesive IGMs - Exhibit Unconfined

Compression Strengths Between 10-100 ksf

• Cohesionless IGMs - Exhibit Blow Counts (N)

Greater Than 50 Blows/Foot Using Standard Penetration Test

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• Hole is Drilled (Pre-bored) Into the IGM Material

and Bottom is Cleaned

• H-Pile Is Placed Into Hole – No Driving (Seated)
• Hole Is Backfilled With Concrete
• Pile Extends Up Into Abutment
• Is the Resulting Deep Foundation Member a

Shaft or a Pile?

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• WisDOT Experience with IGM Varies
• Codes Provide Limited Guidance on Design

Methodology/Pile Capacity in IGM Materials

• Project Used Load Test to Verify Design

Assumptions For Drilled-in Piles

• Lead to a Methodology Used to Design Drilled-

in Piles in IGM Material

• Help Eliminate Some Common Pile Installation

Issues In These Situations

• Goal – Save Money

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• WisDOT Often Designs MSE Walls Around

Abutments

• Reduce Bridge Span Lengths
• Support Abutments on Piles Through MSE Backfill
• Install Piles Prior to Wall Construction
• IGM Materials Make Pile Length Estimates Difficult
• Difficult Driving Often Leads to Pile Alignment Issues
• What About Installing Pre-bored/Backfilled Piles

Into the Very Dense IGM?

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• Alternative Foundations?
• Why Not Use Spread Footings?
• Why Not Use Drilled Shafts?
• Will Address Those Later
• Proper Design Methodology – Shaft or Pile?
• What Corresponding Resistance Factor?
• Cost Effective to Conduct a Pile Load Program?

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• Site Has High-strength Till Soils
• Consultant-Designed Project
• Multi-Year Construction
• Project Had Enough Lead Time to

Accommodate Load Test Program

• Was an Adjacent, On-going Project We Could

Add Load Test Program to

• Results From Load Test Incorporated Into

Project Plans (Pre-Letting)

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Chippewa River

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Chippewa River

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Chippewa River

• Driven H-Piles Using Modified Gates:
• Resistance Factor of 0.50
• Driven H-Piles Using Pile Driving Analyzer:
• Resistance Factor of 0.65
• Drilled Shafts:
• Resistance Factor 0.35-0.5 (No Load Test)
• Bored H-Piles With Static Load Test:
• Resistance Factor of 0.8 (Load Test)
• Resistance Factor of 0.8 (Shaft Spacing)

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• Sometimes Piles Run Very Long (Increased Cost

and Times), or Very Short (Creating a Lateral Resistance Concern)

• Difficult to Achieve Necessary Alignment Above

Driven Elevation – Often Not Aware of This Until After Hammer Leads are Removed

• Adjacent Bridge Experienced Both of These

Issues

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• Larger Diameter/Conflicts With MSE Wall
• Requires Slightly Longer Bridge
• Lower Resistance Factor (No Load Test),

Resulting in Deeper Shafts

• Secant Walls Also Considered – High Cost

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• Multi-span Bridges: WisDOT Typically Does Not

Use Spread Footings on MSE Walls

• Would Require Expensive Full-retaining

Abutments and Wings Instead of MSE Wall

• Early Cost Estimate Indicated Pre-bored Piles

w/Load Test May Be Most Cost Effective Alternative

• Decision: Conduct Load Test of Pre-bored

Hybrid Piles to Confirm Design/Costs

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• Assume Similar Nominal Load to Driven Piles
• Same Number of Support Members
• Same Spacing of Members
• Use to Estimate Shaft Depths Using Static Analysis
• Check To Ensure No Settlement Issues
• Use HP 14x74 Piles
• 30” Pre-bored Holes (Contractor Used 34”)
• Pre-bore to 20’ Below MSE Wall Pad
• Include Side Friction and End Bearing

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• Resistance Factors of 0.8 (Load Test) and 0.8

(Shaft Spacing)

• Only Tested Axial
• Added to Existing Adjacent-Project Contract
• Jim Long Designed and Conducted Load Test
• Standard Test – 1 Test Pile and 4 Reaction Piles
• Load Frame Designed by Contractor
• Davisson Failure Criteria Used – Pile or Shaft?
• $100k Cost

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Chippewa River Top of Shaft Bottom

• f Shaft

Settlement?

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Design Load = 500 Kips

• Follow AASHTO For Shaft Design in IGM
• Nominal Shaft Capacity of 500 Kips
• Resistance Factors
• 0.8 For Using Load Test
• 0.8 For Shaft Spacing
• Total Applied = 0.65 (End Bearing and Side Friction)
• Equates to Factored Load of 325 Kips
• Conservatively Used Design Shaft Depth From

Load Test (Based on Pile Criteria)

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• Same Shaft Depths as Load Test
• Use 14x73 H-Piles With 4” Shear Studs
• 34” Diameter Pre-bored Holes
• Require Full-depth Casing
• Spacing of Piles – 5.5 and 6.0 Feet
• Place Piles in Hole – Firmly Seat (Do Not Drive)
• Socket-in Piles With Concrete – Full Depth
• Piles Extend to Abutment
• No Ground Disturbance Within 10’ for 24 Hours

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• Pile Installation Went Well
• Dry Holes, Cased All the Way Down
• Good Contractor Production
• Able to Keep Alignment
• No Subsurface Pre-boring Surprises
• No Other Issues Noted
• Project Still Being Constructed, But Abutments

and Walls Have Been Completed

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• Based on Comparison to Static Pile Estimates

For Driven Piles and Actual Bid Costs of Pre- bored Piles

• Load Test Costs Removed ($100k)
• Bridge B-13-831 Savings: $200k
• Bridge B-13-832 Savings: $130k
• Possible Total Savings: ≈ $200-330k

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B-13-0831 $208,664.40

B-13-0832 $129,336.40

• Will Consider This Deep Foundation Type on

Future Projects With Similar Subsurface Conditions and Designs

• During Design – Will Estimate Costs to Ensure

This Option is the Most Economical Foundation

• Hope This May Generate Creation of More

Design Guidance

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