Surprises and Solutions When Driving Piles in Mountain Valleys of Vermont

1
Surprises and Solutions When Driving Piles in
Mountain Valleys of Vermont

• Christopher C. Benda, P.E, VTrans
• John E. Lens, P.E., GeoDesign, Inc.

2
Outline

• Introduction
• Design and Construction Approach
• 4 Short Pile Driving Overrun Stories
• Common Characteristics in Overruns
• Why These Matter
• Solutions

3
Introduction

• Problem
• Environment/geology
• Exploration Difficulties

4
Design and Construction Approach

• Explorations Advanced using rotary wash boring
  techniques
• Minimum of 1 boring per foundation element
• SPT testing
• Continuous sampling on first boring to 30 feet
• 5 foot intervals thereafter
• Typically to bedrock
• Unless SPT N gt100 for a depth of 20 feet
• 10 foot rock cores
• Lab testing conducted on soil and rock samples
• Field logs combined with lab classification and
  geologists assessment
• gINT logs generated and incorporated into project
  plans

5
Design and Construction Approach

• Soil profile developed
• Pile lengths estimated using Driven 1.2
• Nordlund-side friction
• Thurman-end bearing
• Meyerhof-limiting end bearing
• Soil properties estimated from correlations with
  N values and profile
• Box perimeter for side friction
• Cross sectional area for end bearing
• Cast shoes not considered in analysis
• Driveability analysis using GRLWeap

6
Design and Construction Approach

• PDA testing specified
• Dense soils or boulders
• Side Friction
• Pile Driving Analyzer (PDA)
• Approved consultants
• Hired by contractor
• Submittals
• Pile Driving Equipment Data Form
• Wave equation analysis for preliminary driving
  criteria
• Capacity on plans
• Subsurface information
• Pile
• Equipment
• Estimated length

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Design and Construction Approach

• System inspection
• PDA testing conducted at first pile on each
  foundation unit
• Saximeter provided by contractor
• Stroke on OED
• Hammer blows
• Restrike at 48 hours
• CAPWAP analysis
• Criteria for remaining piles established

8
Vermont Sites
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Cofferdam Pile Driving
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Lyndon Project

• Bridge Photo

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Lyndon Project

• 80 integral abutment bridge
• 5 HP14x102 per abutment
• 20 loose to dense granular fill
• Medium to very dense gravely sand (Ngt50) with
  scattered cobbles and boulders
• 10 to 20 silt content
• Bedrock between 138 and 155 feet

12
Lyndon Total Skin Friction
13
Huntington
14
Huntington
15
Huntington

• 188 2-span curved girder bridge
• Conventional pile foundations
• 40 feet of dense to very dense sands, sandy silts
  and silts
• Boulders and cobbles with very dense sandy gravel
  horizons to 82 feet
• Abutment 2 similar w/o boulders
• Borings terminated 60-100 feet below footing
  elevation

16
Bristol
17
Bristol

• 144 integral abutment bridge
• 5-HP 14X102 piles per abutment
• 20 of cobbles and boulders
• Medium dense to dense sandy silt
• More boulders at 65
• Borings terminated 90 -100 feet in boulders

18
Bolton
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Bolton

• Rehabilitation of a pair of 5-span bridges
• Replacement of pier 2-NB and pier 3-SB
• Existing piers 2 on HP10X42 and timber piles
• Continuous structure fixed at new piers
• Design called for 12 ¾ pipe piles
• Changed to HP12X53

20
Bolton

• 30 of medium dense silt, 20 feet of medium dense
  sandy silt with gravel
• Very dense sands and gravels to 170 feet
• 20 foot boulder layer encountered at piers at
  135

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Bolton Baffle Plate
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Bolton Pier 2 Dynamic Testing Results
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Predicted and Actual Pile Lengths on Case History
Projects
24
Common Characteristics Piles/Driving

• H-Piles (HP12x53, HP12x74, HP14x102)
• Piles from 50-151 feet long
• Single Acting Diesel Hammers (40-55,000
  foot-pound rated energy)
• 5 to 20 piles per pier/abutment

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Common Characteristics - Soils

• SPT N-values 40 to 100
• Sometimes Frequent Cobbles/Boulders but not
  always
• Silt trace to 25
• Gravelly Sands
• Glacial Tills

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Implications

• Cannot rely on boring refusals for piles
• Need to drill to bedrock to find end bearing
• ??s for Integral Abutment Bridges
• Time Added Project Costs

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Solutions

• Two Tiered Design Approach
• Expand the pile performance database
• Improve prediction skills

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Expand Pile Performance Database

• Standardize driving monitoring/records
• Increase PDA monitoring emphasis
• Share findings (especially DOTs)

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Improve Prediction Skills

• Existing analytical methods
• Myerhof
• Nordlund
• Tomlinson

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Back-calculated Skin Friction
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Consider Displacement Piles

• Concrete filled pipe piles
• Tapered piles

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Summary

• H-piles overruns
• Problematic geologic conditions
• Design implications integral abutments
• Design and construction based response
• Opportunity for a collaboration forum

33
Acknowledgements

• Vermont Agency of Transportation
• GeoDesign, Inc.
• Michael Deery GZA GeoEnvironmental

34
Thank You!

• VT Agency of Transportation vt.gov
• GeoDesign, Inc. geodesign.net