design of helical piles for limited access …
TRANSCRIPT
SEPTEMBER 5 - 7, 2018
DESIGN OF HELICAL PILES FOR LIMITED ACCESS TRANSMISSION LINE
SEPTEMBER 5 - 7, 2018
BACKGROUND
• July 5th, 2016 A STORM EVENT COLLAPSED APPROX. 10 MILES OF PARALLEL 345 KV TRANSMISSION LINES NEAR ROGERS, MN.
• NORTH LINE WAS RECONSTRUCTED WOOD COMPLETE.
• XCEL HIGHLIGHTED 10 STRUCTURES OF CONCERN DUE TO ACCESS AND FOUNDATION REQUIREMENTS TO BE DESIGN STEEL COMPLETE
SEPTEMBER 5 - 7, 2018
SITE CONDITIONS
• VERY SOFT CLAY OVER FIRM.
• WATER TABLE AT OR NEAR THE SURFACE.
• ABNORMAL RAINFALL FLOODED THE LOCATIONS OF FOUNDATION INSTALL.
• SOME LOCATIONS WERE COVERED BY 5 FEET OF WATER
• ONLY ACCESSABLE BY FLOATING MATS.
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TYPICAL SOIL PROFILE
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REASONS FOR STEEL STRUCTURES
• FOUNDATION FOR WOOD POLE – EXPENSIVE– TIME CONSUMING– BANDING OF THREE
DRIVEN WOOD PILES– REQUIRED LARGE
EQUIPMENT– ACCESS CONCERNS
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REASONS FOR STEEL STRUCTURES
• ADVANTAGES OF SMALL DIAMETER HELICAL PILES– SMALL EQUIPMENT– TORQUE TO
CAPACITY RATIO– FIELD MODIFIABLE– MODULAR
SECTIONS
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FOUNDATION DESIGN
• HPS INFORMED XCEL OF NEW GRILLAGE SYSTEM• XCEL SUPPLIED HPS WITH STRUCTURAL LOADS FOR STEEL
H-FRAMES AND DESIGN GEOTECHNICAL INFORMATION.• FOUR DIFFERENT TOWERS WOULD BE DESIGNED FOR.• EXPEDITED CONSTRUCTION REQUIREMENTS DUE TO
STORM DAMAGE.
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HELICAL PILE DESIGN
• 4-PILE HSS 3.5” SCH. 80 HELICAL PILES WITH HELICAL CONFIGURATION OF 10/12/14/14. PILE DEPTH 20 TO 30 FEET.
• REQUIRED WORKING CAPACITIES OF HELICAL PILES WERE DERIVED FROM ENSOFT, Inc GROUP® SOFTWARE.
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ENSOFT, INC GROUP® PLOTS
*ASSUMING FIXED HEAD CONDITION
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HELICAP® HELICAL CAPACITY DESIGN SOFTWARE
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GRILLAGE DESIGN
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GROUTED CONNECTION
• CREATES A FIXED HEAD GRILLAGE CONNECTION.
• 3” TO 4” OF LOCATION TOLERANCE.
• NO WELDING OR BOLTING• CLAMP INSTALLED BY
TORQUING BOLTS OR HYDRAULIC MEANS
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STRUCTURAL DESIGN
• MEMBER SIZING WAS CONDUCTED USING HAND CALCULATIONS.
• FINITE ELEMENT ANALYSIS SOFTWARE WAS ALSO USED FOR MEMBER CAPACITIES AND WELD SIZES
ANSYS ® FINITE ELEMENT SOFTWARE
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INSTALLATION• INSTALLATION BEGAN ON OCTOBER 3, 2016
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CUTTING TO ELEVATION
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INSTALL CLAMP AND SPACER FIXTURE
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GROUTING VOID
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WASHERS AND THREADBAR
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FINISHED CONNECTION
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INSTALLATION SUMMARY
• PRODUCTION RATE– 1 TOWER PER CREW PER DAY.– 2 FOUNDATIONS PER TOWER– INSTALLATON DEPTH 20 TO 30 FEET
• 10 TO 15 MINUTES PER PILE TO INSTALL
– GROUT REQUIRED 7 DAYS TO CURE.
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QUESTIONS?