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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.

SEPTEMBER 5 - 7, 2018

TYPICAL SOIL PROFILE

SEPTEMBER 5 - 7, 2018

REASONS FOR STEEL STRUCTURES

• FOUNDATION FOR WOOD POLE – EXPENSIVE– TIME CONSUMING– BANDING OF THREE

DRIVEN WOOD PILES– REQUIRED LARGE

EQUIPMENT– ACCESS CONCERNS

SEPTEMBER 5 - 7, 2018

REASONS FOR STEEL STRUCTURES

• ADVANTAGES OF SMALL DIAMETER HELICAL PILES– SMALL EQUIPMENT– TORQUE TO

CAPACITY RATIO– FIELD MODIFIABLE– MODULAR

SECTIONS

SEPTEMBER 5 - 7, 2018

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.

SEPTEMBER 5 - 7, 2018

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.

SEPTEMBER 5 - 7, 2018

ENSOFT, INC GROUP® PLOTS

*ASSUMING FIXED HEAD CONDITION

SEPTEMBER 5 - 7, 2018

HELICAP® HELICAL CAPACITY DESIGN SOFTWARE

SEPTEMBER 5 - 7, 2018

GRILLAGE DESIGN

SEPTEMBER 5 - 7, 2018

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

SEPTEMBER 5 - 7, 2018

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

SEPTEMBER 5 - 7, 2018

INSTALLATION• INSTALLATION BEGAN ON OCTOBER 3, 2016

SEPTEMBER 5 - 7, 2018

CUTTING TO ELEVATION

SEPTEMBER 5 - 7, 2018

INSTALL CLAMP AND SPACER FIXTURE

SEPTEMBER 5 - 7, 2018

GROUTING VOID

SEPTEMBER 5 - 7, 2018

WASHERS AND THREADBAR

SEPTEMBER 5 - 7, 2018

FINISHED CONNECTION

SEPTEMBER 5 - 7, 2018

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.

SEPTEMBER 5 - 7, 2018

QUESTIONS?

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