How helical piles work, how they are designed, and what load they carry. Includes a KT table for shaft diameters Ø60.3 to Ø323.9, a capacity table by pile size, and four project cases.
A helical pile is a steel shaft with one or more helical bearing plates welded near the tip. Rotated into the ground, the helix pulls the pile downward like a wood screw into timber. The pile is driven until it reaches a soil layer that carries the design load. The torque needed to turn it gives a direct measurement of capacity at every depth.
The helix generates both compression capacity (downward) and tension capacity (uplift). This separates helical piles from driven and bored piles. Typical uses include solar racking, building foundations, transmission masts, sound barriers, and underpinning.
No excavation, no spoil, no concrete cure. The pile carries load the moment installation stops.
Paalupiste manufactures two ranges in Finland: PRO for commercial, infrastructure, and solar projects up to about 1,000 kN characteristic capacity, and HELIX for residential and lighter structures that install with a handheld drill or compact excavator. Both are EN 1090 CE certified and designed to Eurocode 7 (EN 1997-1).
Helical pile is the North American term. Screw pile is the European, UK, and Australian term. You will also see helical screw pile, helical anchor, and screw anchor. Same product. This guide uses helical pile and screw pile interchangeably.
The first documented screw pile dates to 1838. Irish engineer Alexander Mitchell patented the system for the Maplin Sands Lighthouse at the mouth of the Thames estuary, where soft sediment would not hold a conventional foundation. The piles were turned into the seabed by hand using capstan bars, and the structure stood for almost 100 years.
Through the 19th century, helical piles supported lighthouses, piers, and bridge footings across the British Empire, the United States, and the Baltic. The Wolf Rock and Coney Island lighthouses still stand on their original 19th-century screw piles.
Hydraulic drive heads replaced manual capstans in the 1980s. A small excavator could now generate tens of kilonewton-metres of torque, and installation rates began to match concrete on full-scale projects.
Paalupiste was founded in 2001 in Porvoo, Finland. The company has manufactured over 700,000 helical piles, delivered across Europe, North America, and the Middle East.
Five parts: shaft, helix plate, coupling sockets, drive head adapter, and galvanizing.
Circular hollow section in steel grade S355J2H. Outer diameter Ø60.3 mm to Ø323.9 mm, wall thickness 2.9 to 12.5 mm. Shafts are joined with internal sleeves to extend beyond a single 6 m segment.
One or more circular steel plates pitched to a 50 mm lead, welded to the shaft near the tip. Plate diameter 150 mm to 500 mm. Plate thickness scales with shaft size: 12 mm up to Ø127, 15 mm for Ø139.7, 20 mm for Ø168.3 and above.
Internal sleeves welded to the top of each segment for adding extensions during installation. Standardised bolt patterns across the PRO range.
Square or hex coupling at the top that mates with the hydraulic drive head. HELIX piles take a hex bit for a handheld drill.
Hot-dip galvanizing to EN ISO 1461. Zinc coating typically 70 to 120 microns. In non-aggressive soils the zinc layer lasts 50 to 100 years before wall-thickness loss begins. Steel from SSAB.
Two parts: static capacity from soil parameters, and torque-to-capacity correlation that verifies the design during installation.
The basic relationship:
QT is the ultimate axial capacity (kN). T is the installation torque (kNm) measured at end of installation after the helix has reached design depth. KT is a calibration coefficient (m-1) that depends on shaft diameter, soil type, and installation method. Paalupiste KT values come from internal load tests correlated with installations across Northern European soils.
Values used in Paalupiste design for cohesionless soils. Site-specific calibration is recommended for heavy loads or soils outside this range.
| Shaft diameter | KT (m-1) | Typical T at design capacity |
|---|---|---|
| Ø60.3 mm | 33 | 1.5 to 4 kNm |
| Ø76.1 mm | 29 | 2 to 6 kNm |
| Ø88.9 mm | 24 | 3 to 9 kNm |
| Ø101.6 mm | 21 | 5 to 13 kNm |
| Ø114.3 mm | 18 | 7 to 18 kNm |
| Ø139.7 mm | 15 | 10 to 25 kNm |
| Ø168.3 mm | 12 | 15 to 35 kNm |
| Ø219.1 mm | 10 | 25 to 60 kNm |
| Ø273.0 mm and larger | 8 | 35 to 90+ kNm |
Values reflect Paalupiste design practice for cohesionless soils with effective friction angles between 32 and 38 degrees. For cohesive clays, fills, and layered profiles, contact our engineering team for project-specific calibration.
For a single-helix pile in cohesionless soil, ultimate compression capacity is bearing capacity of the helix plate plus shaft friction over the embedded length. Typical formulation in EU practice is Vesic-Meyerhof with corrections for plate aspect ratio and depth-to-diameter ratio.
Required soil parameters: effective friction angle (φ'), effective cohesion (c'), undrained shear strength (cu) for clays, effective unit weight, and groundwater conditions. CPT data gives a continuous profile of relative density and undrained strength against depth. CPTU is rarely needed for helical piles unless settlement governs.
Paalupiste designs to EN 1997-1 and the relevant National Annex. UK uses Design Approach 1 (DA1, combinations 1 and 2). Continental EU mostly uses DA2. The characteristic resistance Rk is divided by a model factor γR and a correlation factor ξ3 or ξ4, giving design resistance Rd.
For UK helical piles with installation-torque verification, ξ3 is typically 1.4 when each pile is torque-verified individually. Combined factor of safety from characteristic to design capacity is usually 1.8 to 2.4.
Lateral capacity is evaluated with p-y curves for the relevant soil layers. For most building and solar applications, lateral is governed by serviceability deflection limits, not ultimate failure.
"KT depends on shaft size, soil type, and installation method. We publish ours so you can check the maths."
Tero Paunonen, Paalupiste Oy
Typical characteristic compression capacity (Rk) for PRO and HELIX piles in medium-dense to dense cohesionless soil. For early-stage sizing only. Actual capacity depends on soil profile, helix configuration, embedded length, and group or lateral effects.
| Pile | Wall | Helix | Rk typical | Application |
|---|---|---|---|---|
| HELIX Ø60.3 | 2.9 mm | Ø150 to 200 | 10 to 30 kN | Terraces, sheds, decking, small extensions |
| PRO Ø60.3 | 5.0 mm | Ø200 to 250 | 30 to 80 kN | Cabins, light buildings, sound barriers |
| PRO Ø76.1 | 5.0 to 6.3 mm | Ø200 to 300 | 50 to 150 kN | Residential foundations, solar trackers |
| PRO Ø88.9 | 6.3 mm | Ø250 to 400 | 100 to 250 kN | Houses, solar farms, signage masts |
| PRO Ø114.3 | 6.3 mm | Ø300 to 500 | 200 to 500 kN | Commercial buildings, BESS platforms, halls |
| PRO Ø139.7 | 6 mm | Ø400 to 500 | 300 to 700 kN | Industrial, peat foundations, deep piles |
| PRO Ø168.3 | 8 mm | Ø400 to 500 | 400 to 900 kN | Heavy structures, transmission masts |
| PRO Ø219.1 | 8 to 12 mm | Ø500 | 600 to 1,200 kN | Bridge approaches, large infrastructure |
| PRO Ø273 to 323.9 | 10 to 12.5 mm | Ø500 | 1,000+ kN | Custom heavy structures, 110 kV masts |
HELIX is single-helix, handheld drill or compact excavator. PRO is excavator-mounted hydraulic drive head, from residential up to heavy infrastructure. Multi-helix configurations increase capacity per pile and reduce embedment in layered soils, especially for solar.
Tension (uplift) capacity is typically 80 to 95 % of compression for double-helix piles. Lateral capacity is governed by serviceability deflection, not ultimate shaft failure, in Ø88.9 and larger.
Six measurable advantages that change your project economics. Every claim backed by real site data from thousands of installations across Europe.
No excavation, no formwork, no concrete curing. Helical piles screw in and carry load immediately. Your build starts the same day.
Eliminate frost insulation, drainage, and multi-phase earthworks. Fewer work steps, fewer invoices, faster project delivery.
Zero concrete eliminates the largest carbon source in foundation work. 100% steel, 100% removable, 100% recyclable.
Every pile produces a real-time torque trace that confirms capacity at depth. No equivalent measurement exists for a poured concrete footing.
Geotechnical investigation gives the soil profile and parameters. CPT sounds at design locations are usually enough. The pile schedule sets shaft diameter, helix configuration, embedded length, and target torque per pile. Piles ship in 6 m segments with joining sleeves pre-welded.
PRO piles up to Ø88.9 install with 5 to 20 kNm drive heads on 5 to 14 tonne excavators. Heavy piles up to Ø323.9 need up to 90 kNm drive heads on 20+ tonne excavators. Digga PD12, PD25, and HyperTorq+ drive heads are standard, all with calibrated torque sensors and data logging. HELIX piles install with an 18 V brushless drill.
The drive head logs torque against depth in real time. The operator turns the pile until end-of-installation torque reaches the design value (QT = KT × T). The torque log is the per-pile certificate. Under EN 1997-1 with per-pile verification, separate proof load tests are usually not required.
Rates depend on pile size, embedment, and soil. A two-operator team with one excavator-mounted drive head installs 30 to 50 PRO Ø88.9 piles per day in homogeneous sand. 20 to 30 per day in firm cohesive soils. Peak observed rate is 65 per day in favourable ground. Solar farms with multiple drive heads in parallel: 200 to 400 per day per crew.
Each pile gets a report: date, time, GPS, torque, depth, operator. Consolidated reports meet EN 1997-1 verification requirements for building control submission.
Four projects, four different load types and soil profiles.
Other projects: 100+ residential foundations across Europe, sound barriers along major rail and motorway corridors, marina platforms, bridge approaches, and several hundred megawatts of solar. Project data available on request.
Where helical piles do not work, where they are difficult, and where they are often wrongly assumed not to work.
Shallow solid rock. If competent bedrock is less than 1 m below ground, the helix refuses before reaching design embedment. Rock-socketed micropiles or driven piles are the alternative.
Aggressive corrosive soils without mitigation. Low pH, high sulphate, high chloride, or high resistivity can accelerate corrosion beyond standard galvanizing. Designable around with thicker walls, sacrificial wall allowance, or cathodic protection, but soil chemistry must be tested first.
Boulder fill or large rock obstructions. Large rocks in the upper layers stall the pile. May need relocation by a metre or two, pre-augering, or a larger drive head. Adds time and cost but rarely a deal-breaker.
Variable soil profiles. Stratigraphy that changes across the footprint needs pile-by-pile adjustment. Torque verification handles this case directly: each pile is individually verified to capacity.
Peat and very soft soils. Not a hard limit. The design shifts to a longer pile with shaft friction in the underlying competent layer, often with multiple helices for extra bearing. Northern European infrastructure on peat up to 9 m deep is routine.
Cold and frost. Installation runs year-round. Frost heave is resisted by embedment below frost depth, as for any deep foundation.
Standards Paalupiste piles are manufactured, designed, and documented to.
Structural steel under EN 1090-1 factory production control. CE marked to the EU Construction Products Regulation. Audited by Bureau Veritas.
Quality management covering design, manufacturing, traceability, and corrective action. Each pile has a heat number and lot ID traceable to the mill certificate.
Environmental management with documented carbon, waste, and reusable content. Steel from SSAB.
Hot-dip galvanizing. Coating 70 to 120 microns. 50 to 100 year design life in non-aggressive soils.
Geotechnical design to the European code. DA1 in the UK, DA2 in most continental jurisdictions, national annexes applied as required.
Bureau Veritas inspection available for export markets and projects requiring independent verification of materials, welding, and dimensions.
Five factors that drive pricing.
Soft soils need longer piles. Dense soils need bigger drive heads. Layered profiles need design optimisation. CPT data lets us size the pile economically. Most cost surprises come from sites where ground investigation was skipped.
Steel cost scales with cross-section and length. Ø168.3 uses roughly 3x the steel of Ø88.9 at the same length. Multi-helix piles cost more per pile but can reduce total count enough to lower the overall price.
Volume discounts on steel, galvanizing, and crew mobilisation are significant. A 50-pile residential project has a higher unit cost than a 5 000-pile solar farm at the same spec.
Mobilising a drive head and crew to a remote site adds a fixed cost. Restricted access (urban infill, sloping ground, water crossings) needs smaller or specialised machinery, which raises the per-pile rate.
A clear, level site lets the drive head move pile-to-pile in minutes. A constrained, sloping, or vegetated site multiplies cycle time. For repeat-pattern projects like solar, this is the single biggest driver of installation cost.
The helical pile calculator gives early-stage sizing for cohesionless soils. For a project-specific quote, contact us.
Dive deeper into products, technical data, and real-world project examples.
PRO vs HELIX: compare specifications and find your fit
Full comparison tables vs concrete, driven piles, CFA, ground screws
Full range of piles, brackets, adapters, and accessories
Digga and HyperTorq+ drive heads, drills, and torque tools
Real-world helical piling projects with photos and data
Get in touch for project-specific pricing and technical support
Paalupiste delivers across Europe through local partners who handle supply, engineering, and installation in their own market. In the United Kingdom, projects are run by UKHelix, Paalupiste's exclusive UK partner: see helical piles in the UK. In Belgium, Dutch and French-speaking customers are served by Paalupiste Belgium.
