Dan Brown, P.E. DFI Minnesota 2010 1 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
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Dan Brown, P.E. DFI Minnesota 2010
1
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
2
5/4/2012
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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5/4/2012
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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5/4/2012
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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5/4/2012
Cumberland River
Bronx Whitestone Bridge, NYC
Innovative r/c percussion drilling
techniques through boulders & till
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
Case History – Foothills Bridge
Foothills Bridge
Abutment 2
Abutment 1Area of Colluvium
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
Foothills Bridge
Cased zone
4.6 m (15 ft) uncased bond
zone
Anchor (to rock)
Residual Soil
Weathered Rock
Sound Rock
Pier
Foothills Bridge
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
Foothills – Trestle Foundation
Foothills – Pier Foundations
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
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
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
Continuous Flight Auger Piles
Use of Automated Monitoring Systems
Drilled Displacement Piles
Dan Brown, P.E. DFI Minnesota 2010
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5/4/2012
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