01 thornley
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1
PILE DESIGN AND CONSTRUCTION CHALLENGES IN PARTIALLY THAWED ALASKAN SOILS
John D. Thornley, P.E.Golder Associates Anchorage, Alaska
INTRODUCTION
Village of Stebbins on St. Michael Island South side of Norton Sound, near Nome
STEBBINS, AK
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SITE STUDY
SITE MAP
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SITE CHALLENGES
Flood elevation required tanks be 7 feet above existing grade
Thawed and frozen portions of site Construction issues
Location, Schedule, and Access
Climate change and its effect on warm permafrost
Permafrost was “warm” at 30 to 31.8°F
4
SUBSURFACE CONDITIONS
FOUNDATION DESIGN
Both pad and pile foundations evaluated Permafrost in area is highly degraded
Design piles for frozen and thawed conditions Thawed condition was most conservative design
Use PDA in thawed region to select appropriate embedment depth
Drive piles in both frozen and unfrozen regions to same depth
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FOUNDATION DESIGN (CONT.)
16-inch dia. piles with ½-inch thick walls
Embedment depth of 45 feet gave design FOS of 2.5 to 3
Cutting shoes Upper portion of pile coated
to reduce frost heave potential
FOUNDATION INSTALLATION & TESTING
Contractor used an APE D25-42 diesel impact hammer on setting 4
PDA testing performed during driving and restrucktwo days later on 4 piles
50-foot embedment achieved FOS greater than 3.5
Deemed appropriate to reduce potential for thaw settlement in future
Blow per foot should stay below 84 to avoid tip damage
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PILE INSTALLATION ISSUES
Piles in thawed portion of site had no problems All less than 30 blows/foot
Piles in frozen portion met refusal at 16 to 35 feet with blow counts over 100
Now what???
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0
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45
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30 30.5 31 31.5 32 32.5 33 33.5 34 34.5 35Depth Below Ground (ft)
Ground Temperatures (°F)
Stebbins AVEC Tank Farm Construction Test Holes
Test Hole 1
Test Hole 2
OPTIONS CONSIDERED
Decrease embedment depth Pre-drill holes and drive piles Pre-drill holes, steam thaw, and drive piles Add driving shoes and drive using less energy
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CONCLUSIONS
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ACKNOWLEDGEMENTS
Brent Petrie and Matt Metcalf of AVEC David Myers of STG Robert Miner of Robert Miner Dynamic Testing
Thank You
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