recent advances in the selection and use of drilled...
TRANSCRIPT
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
Recent Advances
in the Selection and Use of
Drilled Foundations
Recent Advances
in the Selection and Use of
Drilled Foundations
Dan Brown, P.E., Ph.D.Dan Brown and Associates
Dan Brown, P.E., Ph.D.Dan Brown and Associates
Overview
Micropiles
Continuous Flight Auger Piles
Drilled Displacement Piles
Drilled Shafts
Dan Brown, P.E. DFI Minnesota 2010
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Micropiles
Typically <12” dia
Relies on steel for structural capacity
Installed with lightweight, versatile drilling equipment
Effective in difficult ground conditions
World Trade Center, NYC
Advancements in Micropiles
Standards for design & construction
Higher capacity piles
Improvements in drilling and more versatile drilling rigs
Innovative applications
Dan Brown, P.E. DFI Minnesota 2010
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Micropiles – Design Details
Casing near surface
Center bar(s) through bond zone
AASHTO Design Section 10.9
FHWA Micropile Manual, Dec. 2005
Micropiles – Design Details
Example Cross-sections
Dan Brown, P.E. DFI Minnesota 2010
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Micropiles in Difficult Ground Conditions
Karst
Till & Boulders
Difficult Site Access
Restricted Headroom
Drilled Shaft
Cumberland River
Micropile VE solution for difficult access piers
Drilled through
boulders
Slope Stability
Concerns
Dan Brown, P.E. DFI Minnesota 2010
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Cumberland River
Bronx Whitestone Bridge, NYC
Innovative r/c percussion drilling
techniques through boulders & till
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Case History – Foothills Bridge
Foothills Bridge
Abutment 2
Abutment 1Area of Colluvium
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Foothills Bridge
Cased zone
4.6 m (15 ft) uncased bond
zone
Anchor (to rock)
Residual Soil
Weathered Rock
Sound Rock
Pier
Foothills Bridge
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Foothills – Trestle Foundation
Foothills – Pier Foundations
Dan Brown, P.E. DFI Minnesota 2010
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Continuous Flight Auger Piles
Continuous Flight Auger Piles
Drill rig capabilities – deeper, larger diameter
Control of the drilling process in unstable soils
Control of the casting process for quality control / quality assurance
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Continuous Flight Auger Piles
Use of Automated Monitoring Systems
Drilled Displacement Piles
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Drilled Displacement Piles
Reduce or eliminate spoil
Increased axial resistance
Improve ground
Eliminate risk of subsidence
Drill effort related to axial resistance
Requires heavier, more expensive drilling equipment than CFA
Slower than CFA
Limited depth of penetration
Kentucky Hospital
Drilled displacement columns for ground improvement
Liquefaction mitigation
Bearing capacity for spread footings
Dan Brown, P.E. DFI Minnesota 2010
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Drilled Displacement Piles
Bearing Tests
‐60
‐50
‐40
‐30
‐20
‐10
0
0 100 200 300 400
Displacemetn, m
m
Average Bearing Pressure, kPa
Test 1
Test 2
Test 3
Dan Brown, P.E. DFI Minnesota 2010
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Drilled Shafts
Larger, Deeper Machine Capabilities Oscillator/Rotator Machines
Reverse Circulation
Base Grouting
Verification Testing
Oscillator Equipment
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Rotator Equipment
Seating Casing into Rock
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Considerations
Advantages
Stability of fully cased excavation
Minimal vibrations for casing installation
Easy removal of spoil & obstructions
Avoid or minimize slurry materials
Limitations
Mobilization cost
Equipment support requirements
Potential to become stuck for deep shafts
Non-level base with hammer-grab excavation
Slip-in Can for Column Connection
Oscillator Casing
Slip-in Casing
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Rotator Construction – Huey P. Long Bridge, New Orleans
Huey Long Bridge Shaft/Cap Connection
Isolation Casing
Shaft Cutoff at -11
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Completed Foundation
Surface Texture
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Restricted Headroom with Rotator Casing
Permanent Casing
Moses Wheeler Bridge, Connecticut
Obstructions?
VE solution to cut through existing piling
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Reverse Circulation Top-Drive Drill
Drilling rock socket into schist
Reverse Circulation Drilling Wolf Creek Dam
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Deeper Drilled Shafts
Case History: Wolf Creek Dam, Kentucky
Embankment wall
Secant pile wall
275 ft deep
Wolf Creek Dam Secant Piles
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Base Grouting
-7
-6
-5
-4
-3
-2
-1
0
0 500 1,000 1,500 2,000 2,500 3,000 3,500O-cell load (tons)
Dis
plac
emen
t of
O-c
ell p
late
(in
ches
) -177.8
-152.4
-127.0
-101.6
-76.2
-50.8
-25.4
0.0
0 5 10 15 20 25 30O-cell load (MN)
Dis
plac
emen
t of
O-c
ell P
late
(m
m)
T3(Not Grouted)
Widespread Use of Polymer Slurry
Disposal advantages
Improved side resistance
Benefits in degradable shales
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Verification Testing
Integrity Testing
Load Testing
Verification testing allows performance basis for specification Design-build
Value engineering
ATC, Mississippi River Bridge, St. Louis
O-cells
Cored rock from test shaft excavation
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Summary
Substantial advances across the broad spectrum of drilled foundations: Equipment & drilling capabilities
More diversity in foundation solutions
Verification testing, alternative project delivery allows implementation of innovation