Commercial Foundation Repair in IA, IL and MO, including Peoria, Pekin & Quincy.

Using Commercial Helical Anchors/Tiebacks

Screw Anchor and Soil Nailing in Iowa, Illinois, and Missouri

Commercial Helical Anchor Installation in Burlington, Iowa
Commercial Helical Anchor Installation in Quincy, Illinois

Helical Anchors (also referred to as tiebacks) provide lateral stability to foundation walls and retaining walls with unbalanced earth pressures. Helical anchors can be installed with hand-held equipment, mini-excavators, skid steers, backhoes, trackhoes, or crane-supported rigs so the anchors can be installed in almost any application. This versatility, along with the ability to immediately load and test the anchors, make helicals a convenient and economical solution for a wide variety of projects.

ADVANTAGES

Design Considerations

Helical anchors are a factory-manufactured steel foundation system consisting of a central shaft with one or more helix-shaped bearing plates, commonly referred to as blades, welded to the lead section. Extension shafts, with or without additional helix plates, are used to extend the anchor into competent load-bearing soils. Helical anchors are advanced ("screwed") into the ground with the application of torque.

The terms helical piles, screw piles, helical piers, helical anchors, helix piers, and helix anchors are often used interchangeably by specifiers. However, the term "pier" more often refers to a helical foundation system loaded in axial compression, while the term "anchor" more often refers to a helical foundation system loaded in axial tension.

Determination of Capacity

The ultimate capacity of a helical anchor may be calculated using the traditional bearing capacity equation:

Qu = ∑ [Ah (cNc + qNq)]

Where:
Qu = Ultimate Anchor 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 anchor installation.

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

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

Qu = KT

Where:
Qu = Ultimate anchor 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 anchor shaft. Load testing using the proposed helical anchor and helix blade configuration is the best way to determine project-specific K-values. However, ICC-ES AC358 provides default K-values for varying anchor shaft sizes, which may be used conservatively for most soil conditions. The default value for the Model 150 Helical Anchor System (1.50" square shaft) is K = 10 ft-1.

-- View Our Helical Anchors and Tiebacks Product Specifications document --

Anchor Capacity

The cross section of a square shaft is very compact which can allow the anchor to penetrate more easily through the soil. This compact shape also reduces the stiffness of the cross section and introduces more potential for buckling. These two factors make square shaft helical anchors better suited for tension loads. Supportworks, Inc. therefore recommends their use mainly for these types of applications. Square shaft helical anchors (piles) used in compression should be evaluated on a case by case basis by the project engineer.

Mechanical Axial Capacity (see note):

  • Allowable Tension = 26.5 kips*

* The mechanical tensile capacity of the Model 150 Helical Anchor System is limited by the allowable stress levels dictated by AISC for a high strength bolt in double shear. The allowable tensile capacity of the shaft is actually much higher than this Allowable Tension value.

Torque Limited Axial Design Capacities based on Ultimate Torsional
Resistance of Anchor Shaft = 6,340 ft-lbs**:

  • Ultimate Soil Capacity = 63.4 kips** (with K = 10 ft-1, see note)
  • Allowable Soil Capacity = 31.7 kips (FOS = 2, Allowable System Capacity therefore governed by mechanical capacity = 26.5 kips*)

** This Ultimate Torsional Resistance and its corresponding Torque Limited Capacities are based on laboratory test results from an IAS accredited facility and may only be approached in idealized conditions. Plastic torsional deformations can begin in the anchor shaft near 4,600 ft-lbs. This value may be reached and exceeded in the field by maintaining alignment between the anchor and the drive head, limiting impact forces and torque reversal, and reducing the tendency to "crowd" (push down on) the anchor. Installation through soils with obstructions or high variability may result in impact loading on the anchor. In these cases, achieving high torque values becomes more difficult and a further reduction in the Design Torque Limit may be appropriate.

Note

K = 10 ft-1 is a default value as published in ICC-ES AC358 which can, in many cases, be considered conservative. Higher capacities can often be achieved with site-specific load testing. Allowable capacities based on site testing shall not exceed the Mechanical Axial Capacity.

-- View Our Helical Anchors and Tiebacks Product Specifications document --

Model 150 Helical Anchor System

  • Outer Dimensions = 1.50" x 1.50"
  • Anchor Shaft Yield Strength = 90 ksi (min.)
  • Coupling Hardware: ¾" Grade 8 Bolt with Nut
  • Available Helix Blade Diameters = 6", 8", 10", 12" and 14"
  • Helix Blade Thickness = 0.375"
  • Termination Hardware: 1" Threaded Rod, Tensile Strength = 120 ksi (min.)

-- View Our Helical Anchors and Tiebacks Product Specifications document --

Model 175 Helical Anchor System

  • Outer Dimensions = 1.75" Round Corner Square Bar
  • Anchor Shaft Yield Strength = 90 ksi (min.)
  • Coupling Hardware: (2) ¾" Grade 8 Bolt with Nut
  • Available Helix Blade Diameters = 6", 8", 10", 12" and 14"
  • Helix Blade Thickness = 0.375"
  • Termination Hardware: 1" Threaded Rod, Tensile Strength = 120 ksi (min.)

-- View Our Helical Anchors and Tiebacks Product Specifications document --

Helix Blade Geometry

helix blades

Supportworks' helical anchors feature blades manufactured with a true helix shape conforming to the geometry criteria of ICC-ES AC358. The leading and trailing edges of true helix blades are within one-quarter inch of parallel to each other and any radial measurement across the blade is perpendicular to the anchor shaft. A true helix shape along with proper alignment and spacing of the blades is critical to minimize soil disturbance during installation.

Conversely, blades that are not a true helix shape are often formed to a 'duckbill' appearance. These plates create a great deal of soil disturbance and do not conform to the helix geometry requirements of ICC-ES AC358 since their torque to capacity relationships are not well documented.

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Counties we Serve
Cities in Des Moines County, IA
Burlington
Danville
Mediapolis
Middletown
Sperry
West Burlington
Yarmouth

Cities in Henry County, IA
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Cities in Iowa County, IA
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Cities in Lee County, IA
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Cities in Van Buren County, IA
Birmingham
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Keosauqua
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Cities in Adams County, IL
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Liberty
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Mendon
Paloma
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Quincy
Ursa

Cities in Brown County, IL
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Cities in Dewitt County, IL
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Cities in Hancock County, IL
Augusta
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Bowen
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Colusa
Dallas City
Elvaston
Ferris
Hamilton
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Nauvoo
Niota
Sutter
Warsaw
West Point

Cities in Henderson County, IL
Biggsville
Carman
Gladstone
Lomax
Media
Oquawka
Raritan
Stronghurst

Cities in Iroquois County, IL
Ashkum
Beaverville
Buckley
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Cissna Park
Clifton
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Danforth
Donovan
Gilman
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Martinton
Milford
Onarga
Sheldon
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Watseka
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Cities in Knox County, IL
Abingdon
Altona
Dahinda
East Galesburg
Galesburg
Gilson
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Maquon
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Saint Augustine
Victoria
Wataga
Williamsfield
Yates City

Cities in La Salle County, IL
Dana
Earlville
Grand Ridge
La Salle
Leland
Lostant
Marseilles
Mendota
Oglesby
Ottawa
Peru
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Seneca
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Sheridan
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Tonica
Utica

Cities in Livingston County, IL
Ancona
Blackstone
Chatsworth
Cornell
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Dwight
Emington
Fairbury
Flanagan
Forrest
Graymont
Long Point
Odell
Pontiac
Saunemin
Strawn

Cities in Logan County, IL
Atlanta
Emden
Hartsburg
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Cities in Mason County, IL
Bath
Easton
Forest City
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Manito
Mason City
San Jose
Topeka

Cities in Mcdonough County, IL
Adair
Bardolph
Blandinsville
Bushnell
Colchester
Good Hope
Industry
Macomb
Prairie City
Sciota
Tennessee

Cities in Mclean County, IL
Anchor
Arrowsmith
Bellflower
Bloomington
Carlock
Chenoa
Colfax
Cooksville
Cropsey
Danvers
Downs
Ellsworth
Gridley
Heyworth
Hudson
Le Roy
Lexington
Mc Lean
Normal
Saybrook
Shirley
Stanford
Towanda

Cities in Schuyler County, IL
Browning
Camden
Frederick
Huntsville
Littleton
Plymouth
Rushville

Cities in Tazewell County, IL
Armington
Creve Coeur
Deer Creek
Delavan
East Peoria
Green Valley
Groveland
Hopedale
Mackinaw
Minier
Morton
Pekin
South Pekin
Tremont
Washington

Cities in Warren County, IL
Berwick
Cameron
Gerlaw
Kirkwood
Little York
Monmouth
Roseville
Smithshire

Cities in Woodford County, IL
Benson
Congerville
El Paso
Eureka
Goodfield
Lowpoint
Metamora
Minonk
Roanoke
Secor

Cities in Adair County, MO
Brashear
Gibbs
Greentop
Kirksville
Novinger

Cities in Chariton County, MO
Brunswick
Dalton
Keytesville
Mendon
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Salisbury
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Cities in Clark County, MO
Alexandria
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Luray
Revere
Saint Patrick
Wayland
Wyaconda

Cities in Knox County, MO
Baring
Edina
Hurdland
Knox City
Newark
Novelty
Plevna

Cities in Lewis County, MO
Canton
Durham
Ewing
La Belle
La Grange
Lewistown
Monticello
Williamstown

Cities in Linn County, MO
Brookfield
Browning
Bucklin
Laclede
Linneus
Marceline
Meadville
New Boston
Purdin

Cities in Macon County, MO
Anabel
Atlanta
Bevier
Callao
Elmer
Ethel
Excello
La Plata
Macon
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Cities in Marion County, MO
Hannibal
Maywood
Palmyra
Philadelphia
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Cities in Monroe County, MO
Holliday
Madison
Monroe City
Paris
Santa Fe
Stoutsville

Cities in Putnam County, MO
Livonia
Lucerne
Powersville
Unionville
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Cities in Ralls County, MO
Center
New London
Perry
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Cities in Randolph County, MO
Cairo
Clark
Clifton Hill
Higbee
Huntsville
Jacksonville
Moberly
Renick

Cities in Schuyler County, MO
Coatsville
Downing
Glenwood
Lancaster
Queen City

Cities in Scotland County, MO
Arbela
Gorin
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Memphis
Rutledge

Cities in Shelby County, MO
Bethel
Clarence
Emden
Hunnewell
Lentner
Leonard
Shelbina
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Cities in Sullivan County, MO
Green Castle
Green City
Harris
Humphreys
Milan
Newtown
Pollock
Winigan

Our Locations:

Foundation Supportworks of the Tri States
8910 N. Industrial Rd.
Peoria, IL 61615
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