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 2

 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? 3

 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 4

 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? 5

 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? 6

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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) 8

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Chippewa River 10

Chippewa River 11

Chippewa River 12

 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) 13

 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 14

 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 15

 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 16

 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 17

 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 18

Top of Shaft Chippewa River Bottom of Shaft Settlement? 19

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Design Load = 500 Kips 28

 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) 29

 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 30

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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 38

 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 39

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 42

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