Recent Advances in the Selection and Use of Drilled Foundations

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1 Recent Advances in the Selection and Use of Drilled Foundations Dan Brown, P.E., Ph.D. Dan Brown and Associates Overview Micropiles Continuous Flight Auger Piles Drilled Displacement Piles Drilled Shafts 1

2 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 2

3 Micropiles Design Details Casing near surface Center bar(s) through bond zone AASHTO Design Section 10.9 FHWA Micropile Manual, Dec Micropiles Design Details Example Cross-sections 3

4 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 4

5 Cumberland River Bronx Whitestone Bridge, NYC Innovative r/c percussion drilling techniques through boulders & till 5

6 Case History Foothills Bridge Foothills Bridge Abutment 1 Area of Colluvium Abutment 2 6

7 Foothills Bridge Pier Residual Soil Cased zone Anchor (to rock) 4.6 m (15 ft) uncased bond zone Weathered Rock Sound Rock Foothills Bridge 7

8 Foothills Trestle Foundation Foothills Pier Foundations 8

9 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 9

10 Continuous Flight Auger Piles Use of Automated Monitoring Systems Drilled Displacement Piles 10

11 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 11

12 Drilled Displacement Piles Bearing Tests 0 Average Bearing Pressure, kpa Displacemetn, mm Test 1 Test 2 Test

13 Drilled Shafts Larger, Deeper Machine Capabilities Oscillator/Rotator Machines Reverse Circulation Base Grouting Verification Testing Oscillator Equipment 13

14 Rotator Equipment Seating Casing into Rock 14

15 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 Slip-in Casing Oscillator Casing 15

16 Rotator Construction Huey P. Long Bridge, New Orleans Huey Long Bridge Shaft/Cap Connection Isolation Casing Shaft Cutoff at

17 Completed Foundation Surface Texture 17

18 Restricted Headroom with Rotator Casing Moses Wheeler Bridge, Connecticut Permanent Casing Obstructions? VE solution to cut through existing piling 18

19 Reverse Circulation Top-Drive Drill Drilling rock socket into schist Reverse Circulation Drilling Wolf Creek Dam 19

20 Deeper Drilled Shafts Case History: Wolf Creek Dam, Kentucky Embankment wall Secant pile wall 275 ft deep Wolf Creek Dam Secant Piles 20

21 Base Grouting 0 O-cell load (MN) Displacement of O-cell plate (inches) T3 (Not Grouted) Displacement of O-cell Plate (mm) ,000 1,500 2,000 2,500 3,000 3,500 O-cell load (tons) Widespread Use of Polymer Slurry Disposal advantages Improved side resistance Benefits in degradable shales 21

22 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 22

23 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 23