New Construction Helical Pier System, Foundation Under Pinning

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Helical piles consist of a steel central shaft with one or more helical shaped bearing plates that are sometimes referred to as blades or flights and are welded to the lead section. Extension shafts are used, with or without blades, to extend the unit down into the earth until they reach the proper depth for load-bearing and capacity. Brackets at the tops of the piles are used to attach the pile to a structure, whether new or in a retrofit application.

Helical piles, screw piles, helical piers, helical anchors, helix piers and anchors are all used interchangeably by most people though the term pier usually refers to a helical pile loaded in axial compression while the term anchor usually refers to a helical pile loaded in axial tension.

Design Considerations

commericial-helical-installationHelical piles are designed such that most of the axial capacity of the pile is generated through bearing of the helix blades against the soil. The helix blades are typically spaced three diameters apart along the pile shaft to prevent one blade from contributing significant stress to the bearing soil of the adjacent blade. Significant stress influence is limited to a ‘bulb’ of soil within about two helix diameters from the bearing surface in the axial direction and one helix diameter from the center of the pile shaft in the lateral direction. Each helix blade therefore acts independently in bearing along the pile shaft.

Multiple piles shall have a center to center spacing at the helix depth of at least four (4) times the diameter of the largest helix blade (ICC-ES AC358). The tops of the piles may be closer at the ground surface but installed at a batter away from each other in order to meet the spacing criteria at the helix depth. For tension applications, the uppermost helix blade shall be installed to a depth of at least twelve (12) diameters below the ground surface (ICC-ES AC358).

Foundation SupportworksTM Model 287 Helical Pile System

Technical Specifications

  • Outside Diameter (O.D.) = 2.875″
  • Wall Thickness = 0.203″
  • Pile Shaft Yield Strength = 60 ksi (min.)
  • Coupling Hardware: (2) ¾” Grade 8 Bolts with Nuts
  • Available Helix Blade Diameters = 8″, 10″, 12″, and 14″
  • Helix Blade Thickness = 0.375″
  • New Construction Bracket: ¾” x 6″ Square A36 Plate (for allowable compression capacities up to 60.0 kips)
  • New Construction Bracket Hardware: (2) ¾” Grade 8 Bolts with Nut
Bracket Specifications

  • Bracket: Weldment manufactured from 0.25″, 0.375″, and 0.50″-thick steel plate.
    Yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.).
  • External Sleeve: 3.50″ OD x 0.216″ wall x 30″ long with sleeve collar welded to one end.
    Yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.).
  • Bracket Cap: 5.0″ wide x 9.0″ long x 1″ thick plate with confining ring welded to one side.
    Yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.).
  • All-Thread Rod: 0.75″ diameter x 16″ long, zinc plated. Grade B7, tensile strength = 125 ksi (min.)

Foundation SupportworksTM Model 288 Helical Pile System

Technical Specifications

  • Outside Diameter (O.D.) = 2.875″
  • Wall Thickness = 0.276″
  • Pile Shaft Yield Strength = 60 ksi (min.)
  • Coupling Hardware: (2) ¾” Grade 8 Bolts with Nuts
  • Available Helix Blade Diameters = 8″, 10″, 12″, and 14″
  • Helix Blade Thickness = 0.375″
  • New Construction Bracket: ¾” x 6″ Square A36 Plate (for allowable compression capacities up to 60.0 kips)
  • New Construction Bracket Hardware: (2) ¾” Grade 8 Bolts with Nut
Bracket Specifications

  • Bracket: Weldment manufactured from 0.25″, 0.375″, and 0.50″-thick steel plate.
    Yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.).
  • External Sleeve: 3.50″ OD x 0.216″ wall x 30″ long with sleeve collar welded to one end.
    Yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.).
  • Bracket Cap: 5.0″ wide x 9.0″ long x 1″ thick plate with confining ring welded to one side.
    Yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.).
  • All-Thread Rod: 0.75″ diameter x 16″ long, zinc plated. Grade B7, tensile strength = 125 ksi (min.).

View our product brochure and product specifications documents.

Foundation SupportworksTM Model 350 Helical Pile System

Technical Specifications

  • Outside Diameter (O.D.) = 3.5″
  • Wall Thickness = 0.313″
  • Pile Shaft Yield Strength = 60 ksi (min.)
  • Coupling Hardware: (4) 1″ Grade 8 Bolts with Nuts
  • Available Helix Blade Diameters = 8″, 10″, 12″, and 14″
  • Helix Blade Thickness = 0.375″
  • New Construction Bracket: ¾” x 6″ Square A36 Plate (for allowable compression capacities up to 60.0 kips)
Bracket Specifications

  • Bracket: Weldment manufactured from 0.25″, 0.375″, and 0.50″-thick steel plate.
    Yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.).
  • External Sleeve: 3.50″ OD x 0.216″ wall x 30″ long with sleeve collar welded to one end.
    Yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.).
  • Bracket Cap: 5.0″ wide x 9.0″ long x 1″ thick plate with confining ring welded to one side.
    Yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.).
  • All-Thread Rod: 0.75″ diameter x 16″ long, zinc plated. Grade B7, tensile strength = 125 ksi (min.).

Determination of Capacity

helical-pier-tech The ultimate capacity of a helical pile may be calculated using the traditional bearing capacity equation:

Qu = ∑ [Ah (cNc + qNq)]
Where:
Qu = Ultimate Pile Capacity (lb)
Ah = Area of Individual Helix Plate (ft2)
c = Effective Soil Cohesion (lb/ft2)
Nc = Dimensionless Bearing Capacity Factor = 9
q = Effective Vertical Overburden Pressure (lb/ft2)
Nq = Dimensionless Bearing Capacity Factor

Total stress parameters should be used for short-term and transient load applications and effective stress parameters should be used for long-term, permanent load applications. A factor of safety of 2 is typically used to determine the allowable soil bearing capacity, especially if torque is monitored during the helical pile installation.

Like other deep foundation alternatives, there are many factors to be considered in designing a helical pile foundation. Foundation SupportworksTM recommends that helical pile design be completed by an experienced geotechnical engineer or other qualified professional.

Another well-documented and accepted method for estimating helical pile capacity is by correlation to installation torque. In simple terms, the torsional resistance generated during helical pile installation is a measure of soil shear strength and can be related to the bearing capacity of the pile.

Qu = KT
Where:
Qu = Ultimate Pile Capacity (lb)
K = Capacity to Torque Ratio (ft-1)
T = Installation Torque (ft-lb)

The capacity to torque ratio is not a constant and varies with soil conditions and the size of the pile shaft. Load testing using the proposed helical pile and helix blade configuration is the best way to determine project specific K-values. However, ICC-ES AC358 provides default K-values for varying pile shaft diameters, which may be used conservatively for most soil conditions. The default value for the Model 288 Helical Pile System (2 7/8-inch diameter) is K = 9 ft-1.

Reviews

"We were very satisfied with the job did for us. The office staff was excellent and very informative. The specialist's presentation was good. We hired your company because we heard good things about you and your products."- Scott & Jess B., 5/5 stars
"Very good job, very satisfied. The installation crew were good hard workers. The salesman was very knowledgeable and answered all my questions. Thank you, I will recommend you!"- Leslie Z., 5/5 stars
"The installation crew, salesman, and office staff were all great!"- Janice O., 5/5 stars
The installation crew worked well together and were polite, professional, and very hard working! Thank you, I have been able to move my wall back to level with your wall anchoring system. I am happy and relieved to have the wall secured and anchored!- Karmen N., 5/5 stars
Blackburn Basement Systems is an experienced company, and they were very courteous. We are very satisfied with a job well done!- Howard A., 5/5 stars
They know their job and did the work in a timely manner! My experience with the office and crew was excellent!- Charlotte P., 5/5 stars
Blackburn Basement Systems is a local business with a good reputation. Of all the construction/repair people I have had work on my house, your crew was the best. They checked in and out, explained the process step by step, and answered all my questions. Blackburn's piering system did the trick!- Gary H., 5/5 stars
We are thoroughly pleased with the WaterGuard system that Blackburn installed. Alan and his crew are very good people, hard working and explained everything well. Great job!- Richard L., 5/5 stars
We couldn't be more satisfied with the anchor system! Our walls are now secure. We chose Blackburn Basement Systems to fix our basement based on a list of excellent references in our area, and good word of mouth.- Michael M., 5/5 stars
Very satisfied, glad we have no water in the basement anymore! Your company did an excellent job fixing my basement, I hope you pay your workers a lot because they work really hard and deserve it!- Ms. Patty K., 5/5 stars
I picked Blackburn Basement Systems because of their outstanding reputation! I was glad that Blackburn provided me with a list of references and local people to talk to about the kind of work that they do.- Bruce C., 5/5 stars
Blackburn's installation crew was knowledgeable, professional, and answered all of my questions well.- Thomas E. II, 5/5 stars
The anchor system works great! Were very pleased with the references provided of local people-helped make our decision much easier.- Charles S., 5/5 stars
Blackburn was able to do everything that needed to be done with quality materials, and good workers. It is such a piece of mind now when rain comes we don't have to clean up water, and that we can use our basement for other things, and that the air is so much better. It's like having a new basement!- Susan and Leon A., 5/5 stars
Absolutely impressed with your WaterGuard system! Glad to know that we have the best waterproofing system and a written warranty!- Terri C., 5/5 stars
We have never detected any leakage since the work was done. The system has done the job that we were told it would.- Chad B., 5/5 stars
Glad we can finally finish our basement off now that it is waterproofed!- Leo E., 5/5 stars
We were well satisfied with a job well done! The inspector and the office were pleasant to work with, and the WaterGuard system seemed to make complete sense. Great work guys!- Jim W., 5/5 stars

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