Advances in the the Use of Drilled Foundations Dan Brown, P.E., Ph.D. President, Dan Brown and Associates, and President, Deep Foundation Institute
Overview !
Why drilled foundations? !
Micropiles
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Continuous Flight Auger (CFA) Piles and Drilled Displacement (DD) Piles
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Drilled Shafts (Bored Piles)
Micropiles !
Typically <12” dia
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Relies on steel for structural capacity
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Installed with lightweight, versatile drilling equipment
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Effective in difficult ground conditions World Trade Center, NYC
Advancements in Micropiles !
Standards for design & construction
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Higher capacity piles
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Improvements in drilling and more versatile drilling rigs
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Innovative applications
Micropiles – Design Details !
Casing near surface
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Center bar(s) through bond zone
AASHTO Design Design Section 10.9
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FHWA FHW A Micropile Manual, Dec. 2005 2 005
Micropiles – Design Details !
Example Cross-sections
Micropiles in Difficult Ground Conditions !
Karst
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Till & Boulders
Difficult Site Access
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Restricted Headroom
Drilled Shaft
International Marketplace, Hawaii Micropiles up to 90m deep in soft alluvium
(photo courtesy of Hayward-Baker)
Case History – Foothills Bridge
Foothills Bridge Area of Colluvium Abutment 1 Abutment 2
Foothills Bridge Pier
Residual Soil
Cased zone
Anchor (to rock)
4.6 m (15 ft) uncased bond zone
Weathered Rock
Sound Rock
Foothills Bridge
Foothills – Trestle Foundation
Foothills – Pier Foundations
Rouchleau Mine Crossing, Minnesota
Pier Foundations
52m
Pile Location in Mine Dump Fill
107m
History
Downhole Hammer Drill Crossover Sub-Seal Crossover Sub Port Shock Absorber Hammer Pilot Bit
Drill Head and Casing Ring Bit
Drilling
Final Pile Design Approximate depth 55m
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762mm dia steel pipe filled with concrete
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End bearing on hard rock
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Design axial resistance = structural capacity of the pile cross section
Note: !
two 600mm dia test piles loaded to 17MN
Continuous Flight Auger Piles
Continuous Flight Auger Piles !
Drill rig capabilities – deeper, larger diameter
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Control of the drilling process in unstable soils
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Control of the casting process for quality control / quality assurance
Continuous Flight Auger Piles !
Drill rig capabilities
Continuous Flight Auger Piles Control of the Drilling and Concreting Process
Drilled Displacement Piles
Drilled Displacement Piles !
Reduce or eliminate spoil
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Requires heavier, more expensive drilling equipment than CFA
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Increased axial resistance
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Improve ground
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Slower than CFA
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Eliminate risk of subsidence
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Limited depth of penetration
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Drill effort related to axial resistance
Kentucky Hospital !
Drilled displacement columns for ground improvement
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Liquefaction mitigation
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Bearing capacity for spread footings
Drilled Displacement Piles
Bearing Tests
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Drilled Shafts (Bored Piles) !
Larger, Deeper Machine Capabilities !
Oscillator/Rotator Machines
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Reverse Circulation
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Base Grouting
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Verification Testing
Oscillator Equipment
Rotator Equipment
Seating Casing into Rock
Considerations Advantages !
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Stability of fully cased excavation Minimal vibrations for casing installation Easy removal of spoil & obstructions Avoid or minimize slurry materials
Limitations !
Mobilization cost
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Equipment support requirements
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Potential to become stuck for deep shafts
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Non-level base with hammer-grab excavation
Rotator Construction – Huey P. Long Bridge, New Orleans
Huey Long Bridge Shaft/Cap Connection
Isolation Casing Shaft Cutoff at -11
Completed Foundation
Surface Texture
Restricted Headroom with Rotator Casing Moses Wheeler Bridge, Connecticut Permanent Casing
Obstructions? VE solution to cut through existing piling
Reverse Circulation Top-Drive Drill
Drilling rock socket into schist
Reverse Circulation Drilling Wolf Creek Dam
Deeper Drilled Shafts Case History: Wolf Creek Dam, Kentucky Embankment wall
Secant pile wall
275 ft deep
Wolf Creek Dam Secant Piles
Base Grouting 0
5
O-cell load (MN) 15
10
20
25
30
0
0.0
-1 ) s e h c n i ( -2 e t a l p l l e -3 c O f o t -4 n e m e c a l p -5 s i D
-25.4 ) m m -50.8 ( e t a l P l l -76.2 e c O f o -101.6 t n e m e c a l -127.0 p s i D
T3 (Not Grouted)
-6
-152.4
-7
-177.8 0
500
1,000
1,500 2,000 O-cell load (tons)
2,500
3,000
Load test data from John James Audubon Bridge, Mississippi River, Louisiana
3,500
Widespread Use of Polymer Slurry !
Disposal advantages
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Improved side resistance
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Benefits in degradable shales
Widespread Use of Polymer Slurry
Polymer Slurry in Shale at Bond Bridge Sample
River Water Polymer Slurry
Natural Moisture Content (%) 8.3 8.3
Slake Durability Index Type Id(2) (%) II 72.2 II 98.2
Durability Rating Based on Shear Strength Loss Type DR s Intermediate 61.9 Hard, more durable 78.6
Load test: 800 kPa unit side resistance After 4 days exposure
Influence on Axial Resistance f 1.6 s k1.4 , e c1.2 n a 1 t s i s0.8 e R0.6 e d i 0.4 S t i 0.2 n U 0
Polymer Bentonite
0
0.5
1
1.5
2
Axial Displacement, inches
Data from Auburn University National Geotechnical
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Research Site (Brown, ASCE GT Journal, 2002)
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Verification Testing !
Integrity Testing
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Load Testing
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Verification testing allows performance basis for specification !
Design-build
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Value engineering
ATC, Mississippi River Bridge, St. Louis O-cells
Cored rock from test shaft excavation
