Helical pile calculations
Screw piles can be used for different applications in residential, industrial, commercial, street lighting etc., they have the advantage of being immediately functional. They can carry the vertical loads, lateral and moment loads right after their installation. They act as deep foundations, anchors (transmission towers …) or tie-backs for retaining walls ….
Firstly, GoliathTech engineers analyze the architectural and structural drawings as well as the geotechnical report when it is available to verify the feasibility of the screw piles and their application according to the applicable codes.
The geotechnical reports, in addition to giving the soil parameters for the calculation of piles, provide information on soil hazards such as the expansion and compressibility of soils, the sensitivity of clay soils, liquefiable soils … The piles are a viable and recognized option in the pile industry as long as they take into account all these soil phenomena in the calculations.
The helical piles must be designed to ensure the transfer of the loads to the soil, without altering their strength and respecting the allowable deflections and settlements. A pile with a lateral load applied at the pile head reacts differently depending on whether the pile head is embedded in the concrete or attached to a beam at a certain distance from the ground.
A safety factor is used according to the contract documents or local codes.
Helical (screw) piles are mentioned in the following codes :
Section 1810.2.2 – Stability
Section 1810.2.1 – Lateral Support
Section 1810.3.3.1.9 – Helical Piles
AC358 – Helical Pile Systems and Devices
Canadian Foundation Engineering Manual 4th Edition
126.96.36.199 Helical (Screw) Piles
CNRC Certifications, evaluations and standards (Canada)
GoliathTech owns an apparatus for compression and tension testing conform to ASTM 1143 and ASTM 3689.
A signed and sealed certificate attesting to the conformity of the installation of the helical piles is required in Canada, the engineer must review the loads of the building or structure and the installation torque provided by the certified installer for each helical pile.
Helical Piles: A Practical Guide to Design and Installation from Howard A. Perko
To offer adequate corrosion protection, GoliathTech offers fully galvanized helical piles as well as accessories. It is important to note that there is a difference between steel that has been hot-dipped galvanized and steel that has been painted or plated to resemble hot dipped-galvanization.
Pile Layout and shop drawings
A pile layout of the location of the piles is given to the franchisee when required for installation. Our stamped shop drawings are available for review by the engineer of record.
Pile Shaft Capacity
- Compression – Tension
In the case where the loads are not mentioned in the contract drawings or for dwelling, GoliathTech uses software such as Robot Structural Analysis to determine the loads that will be applied to each pile by modeling the building. The software simulates the structure above the piles and distributes the loads among the screw piles to provide the precise load per pile.
The compression capacity of the piles should be checked for buckling with the effective length and the end conditions as required by the steel building codes.
The tension loads must also be considered for the helical piles as well as for the helical pile head and its connection to the structure and the helical pile.
Light structures such as boardwalks and solar panels must be checked for adfreeze especially as the weight of the structure is low.
The mechanical resistance can be used if the piles bear directly on bedrock.
- Lateral Loads
When the piles are subjected to lateral loads, they are designed with LPILE or GROUP if it is a group of piles embedded in the same concrete foundation, the slope of the ground must be considered.
The lateral resistance of the helical pile is a function of the load and its arm (the gap between the head and the ground level) and the head condition (free to rotate or fixed).
The minimum depth for the lateral resistance is given by LPILE.
Helix Plate Capacity
The number and diameters of the helices are calculated to carry the compression and tension loads. The distance between the helices is equal to 3 times the minimum diameter.
The calculation of the helices depends on the type of soil, clay or granular, the level of the water table must be known.
GoliathTech helices are conform to the standard CSA G40.21 50 W and use steel with a 60 KSI yield (Fy = 60ksi) which provides an ultimate tensile strength of 70 KSI (Fu = 70 ksi). The helix is positioned 4.5” (114 mm) from the tip of the helical pile and fully welded on both sides of the helix. Helix diameters range from 8” (228 mm) up to 39” (990 mm).
Bracket Capacity and accessories
The transfer of loads is done through the connections, these must be properly designed to take the lateral, compression and tension loads. The heads are designed by finite element method with PTC CREO and IDEASTATICA software
Every project requires a different type of attachment from the structure to the helical pile. The important aspect is to verify that these helical pile heads offer uplift resistance in order to conform to the tension values, lateral resistance, compression resistance, bending resistance, . A helical pile head attachment can be both fixed and adjustable. GoliathTech offers fixed head attachments that are installed with bolts as well as adjustable heads installed with threaded rods.
GoliathTech bolts and threaded rods meet or exceed the standard SAE J429 Grade 5.