Technical Review: Performance, Design, and Deployment of Steel Helical Pile Groups for Transmission Infrastructure

Abstract

Worldwide transmission-grid expansion requires extensive construction of new tower foundations across diverse geological, environmental, and logistical conditions, while conventional bored piling faces increasing cost, schedule, constructability, and adaptability constraints. Steel helical pile groups have been proposed as an alternative, but a systematic evaluation of their suitability for Australian transmission infrastructure has been lacking. This narrative review synthesizes Australian and international case studies, current design standards, and published installation-productivity models to compare helical and bored piles on installation logistics, quality assurance, structural and lateral load performance, environmental footprint, and the under-examined implications of foundation type on tower earthing and lightning performance. The comparison finds that helical piles offer real-time, torque-based capacity verification, immediate load-bearing capacity, and lower labor intensity under favorable ground conditions. However, shallow competent bedrock, dense gravels or boulder-affected ground, and very high lateral-load structures favor bored piles or hybrid solutions, and helical-pile grounding performance for tower earthing has not yet been independently verified. These findings indicate that helical piles are a resilient, logistically efficient alternative to bored piles for much of Australia’s transmission foundation demand when applied on a site-specific basis, and the review recommends Australian design guidance and further grounding-performance research.

1. Introduction

Transmission infrastructure is the network of high-capacity power lines, towers, substations, and related equipment that transports electricity over long distances from where it is generated (such as power plants) to the local distribution systems that deliver it to homes and businesses [1].

Foundations are not just a main part of transmission infrastructure; they are the critical, non-negotiable base upon which the entire system depends [2]. While the tall towers and high-voltage wires are the most visible parts of the transmission system, the foundations are their unseen, indispensable anchor. They are the first component built and the most critical to the system’s structural integrity, safety, and longevity [3]. If a foundation fails, the tower can collapse, and a single tower failure can bring down an entire line, causing a blackout [3].

The foundation must resist being constantly subjected to weather cycles (freeze–thaw, wet–dry), corrosion from soil and water, and potential seismic activity during its lifespan [4,5]. The foundation for a tower must resist four primary types of loads. The first is compression, which is the downward, crushing force from the structure’s own constant weight. The second is tension or uplift, which is the opposing upward force, typically caused by strong wind attempting to pull one side of the foundation out of the ground. The most critical load is the overturning moment, a powerful twisting action created by wind pressure that tries to rotate the entire tower over. This moment is the root cause of the extreme compression and tension on opposite sides of the base. Finally, shear or lateral load is the direct sideways shove from the wind, trying to slide the foundation horizontally through the soil [2]. Figure 1 shows a schematic of the loads applied to a helical pile [6].

Figure 1. Schematic of the primary types of installation loads on a deeply embedded helical pile with a double helix (adapted from Todeshkejoei et al.) [6].

Considering all of the above, foundation design and construction are of great importance, and a small failure of foundations can lead to catastrophic results. Designing an appropriate foundation is a very complicated process, and there is no one-size-fits-all solution. There are several types of foundations encountered for each practice, which are entirely dependent on the local geology, soil conditions, environmental considerations, etc. Drilled shaft, direct embedment, spread footing, grillage, driven piles, and anchors are among the many foundation types shown in Figure 2 [7].

Figure 2. Representative transmission-tower foundation types: drilled shaft, direct embedment, spread footing, driven piles, anchors, and grillage foundation [7].

Bored piles, also known as drilled shafts or caissons, are a fundamental and widely used type of deep foundation, and they are considered an essential method in transmission infrastructure and civil engineering [8]. They are the essential solution when structures must be founded on stable ground that lies far beneath the surface [9]. As shown in Figure 3, a bored pile is a deep foundation element constructed by drilling a cylindrical hole deep into the ground, installing a steel reinforcement cage, and filling the hole with concrete [10].

Figure 3. Construction process of a bored pile: (a) drilling process, (b) hole drilled, (c) reinforcement installed, (d) concrete poured, (e) finished pile (adapted from Mo et al.) [10].

Although bored piles offer high axial and lateral load capacity, flexibility in depth and diameter, relatively low installation vibration, and the ability to be constructed in challenging ground using casing or drilling slurry, their installation involves cost, schedule, logistical, and constructability constraints that may limit their suitability for some projects [10,11].

Firstly, they are generally more expensive than shallow foundations due to the required equipment and materials. Huge drilling equipment and machines for making and pouring concrete into holes all lead to high logistical costs. The transportation of this heavy equipment to the foundation site is also an extra problem, which may even make a project impossible in remote areas [12]. Moreover, the implementation of bored piles usually requires a large workforce, and the rate of steel installation and concrete pouring is influenced by the experience and number of steel crews. Thus, the project expenses are usually high [13].

Secondly, the construction process is less visible (underground), so rigorous inspection is needed to ensure the hole is clean, straight, and properly filled with concrete [13]. Concrete takes a long time to cure, and for this reason, the installation of bored piles is usually a long-term process [14]. Moreover, the production of concrete is a major global contributor to carbon emissions, and concrete is an indispensable part of bored piles [15].

Finally, the environmental performance of a foundation system is an increasingly important consideration for large-scale infrastructure projects. Bored piles require the removal of large volumes of soil and their relocation elsewhere, which negatively influences the environment and endangers its balance [16]. Besides this, the capacity of a bored pile is highly dependent on soil conditions, requiring thorough geotechnical investigation. Before construction of a bored pile, a pre-investigation is vital, which only includes statistical sample analysis around the foundation but does not cover the entire area. The existence of soil types with different cohesion or stiffness from site to site, the existence of natural obstacles, etc., make it very difficult to predict the load-bearing capacity of a bored pile before construction [13].

Given the substantial foundation demand anticipated for Australia’s future transmission grid expansion, conventional bored pile installation is likely to impose considerable cost and schedule burdens, alongside environmental concerns from soil disturbance and spoil handling. Consequently, the adoption of novel or alternative foundation systems represents an increasingly essential direction for the foundation industry, particularly for large-scale, geographically dispersed infrastructure projects such as transmission networks.

1.1. Context and Market Need: The Impetus for Transmission Expansion

Australia is undergoing a profound and rapid energy transformation, driven by a national commitment to decarbonization and the urgent need to replace aging fossil fuel assets. The Australian Government’s “Rewiring the Nation” program is a cornerstone of this policy, providing concessional finance to modernize the electricity grid and deliver new and upgraded infrastructure. This initiative is designed to lower the cost of essential infrastructure for consumers and support Australia’s emissions reduction targets of 43% by 2030 and net-zero emissions by 2050 [17].

The scale of this transition is immense. The Australian Energy Market Operator’s (AEMO) 2024 Integrated System Plan (ISP), which serves as a roadmap for the National Electricity Market (NEM), forecasts that an estimated 4581 km of new transmission lines are needed to meet 2030 targets alone. The optimal development path to net-zero by 2050 has an annualized capital cost of $122 billion, of which transmission investment accounts for $16 billion. AEMO projects that the investment in these transmission projects will recoup their $16 billion investment costs, save consumers a further $18.5 billion, and deliver $3.3 billion in emissions reductions [18].

This national agenda includes several priority transmission projects across the country. In New South Wales, this includes HumeLink, the Sydney Ring, and the Victoria–New South Wales Interconnector West (VNI West). In Tasmania, the Marinus Link and North West Transmission Developments (NWTD) are receiving significant government funding. The government has also agreed to support transmission upgrades in Western Australia and the Northern Territory, highlighting the national scope of the modernization effort [18].

A key challenge highlighted in AEMO’s analysis is the unprecedented increase in costs observed across the energy sector in recent years. These increases are driven by supply-chain constraints and global competition for electricity infrastructure assets, as well as workforce and skills shortages [18]. In this context, the choice of a foundation system transcends a simple technical decision; it becomes a critical component of project risk management. A foundation method that can mitigate these pressures by being faster, requiring less labor, and having a more streamlined supply chain than traditional concrete-based foundations becomes a strategic advantage. This elevates the discussion from a simple engineering choice to a core component of project risk management and accelerated delivery to meet the nation’s energy goals.

Beyond technical design compliance, Australian transmission projects are delivered inside a regulated investment and procurement environment where early-works definition, latent-condition exposure, and program certainty materially influence foundation selection. For major network augmentations, Transmission Network Service Providers (TNSPs) commonly seek regulatory approval and funding for enabling activities (e.g., land access, environmental/geotechnical investigations, route refinement, constructability development) before committing to full construction. A practical illustration is the North West Transmission Developments (NWTD) Stage 1 early works, where the Australian Energy Regulator approved AUD 167.3 million (2024–2025) for TasNetworks to progress early works that de-risk delivery prior to the construction phase [19]. Such early-works packages are intended to reduce downstream uncertainty; however, they also surface a central commercial risk: residual ground-condition uncertainty is priced into tenders and can escalate if site data maturity is insufficient at award. Standard-form contracting in Australia, such as AS 4000, provides a general framework for risk and responsibility allocation among principals, contractors, and project managers, which underpins how commercial risk is distributed across parties on major infrastructure projects [20].

Program certainty in power transmission projects is commonly constrained by approval-gated milestones and stakeholder-related delays, which can erode both projected market benefits and social license. A comprehensive review of causes of delay across power transmission projects identifies land acquisition, regulatory approvals, environmental clearances, and stakeholder engagement as recurring sources of schedule slippage, alongside the sequencing of feasibility studies, tendering, land development, foundation work, erection, and installation. Power sector infrastructure projects have been shown to incur substantial average time overruns, indicating that approval and access-gated milestones represent a structural, rather than exceptional, feature of transmission project delivery [21].

Another delivery constraint is workforce saturation, which increases the probability that schedule milestones translate into cost escalation and program blowouts, especially in regional corridors where multiple transmission programs compete for labor. Infrastructure Australia estimates Australia’s infrastructure workforce at ~204,000 (October 2025) with an immediate shortfall of ~141,000, potentially rising to ~300,000 by 2027. As the pipeline peaks, labor shortages and labor cost pressures are repeatedly identified as substantial delivery risks by surveyed firms [22].

From an insurer and underwriter perspective, foundation selection is relevant not only because it affects ultimate geotechnical performance, but also because it changes the project’s risk transparency, evidentiary record, and dispute exposure. Geotechnical engineering is distinguished from many other design disciplines by the natural variability of the ground and the persistent scarcity of complete subsurface information; as a result, uncertainty is not eliminated at the tender stage but instead must be allocated, monitored, and contractually managed throughout design and construction [23,24]. In practice, this has direct implications for EPC and design-and-construct delivery models, where unresolved foundation uncertainty commonly migrates into higher contractor contingency, conservative detailing, tighter contractual exclusions, and more contentious interface management between client, designer, and constructor. Spross et al. [24] observe that common contractual disputes in geotechnical projects arise from vague clauses regarding risk sharing, especially where the ownership of additional time and cost consequences is unclear. Consistent with this, Hatem [25] showed that geotechnical baselines are not merely technical descriptors of subsurface conditions, but instruments with explicit professional liability implications, because they influence how design assumptions, contractor pricing, and subsequent responsibility for differing conditions are judged. For this reason, a foundation solution that reduces ambiguity in subsurface response can improve the quality of EPC risk allocation and reduce the likelihood that foundation-related claims evolve into professional negligence or indemnity disputes [24,25].

This issue also extends to professional indemnity insurance (PII). While peer-reviewed evidence directly linking foundation type to PII premiums is limited, recent construction-insurance research shows that the use of PII is strongly influenced by the project’s legal framework, premium environment, and exposure to design error or omission, indicating that insurability is closely tied to how technical risk is defined and controlled [26].

Bored piles remain comparatively opaque after construction. This is because defects may arise from slurry, casing, concrete placement, reinforcement positioning, or workmanship, and since 100% inspection is often impractical, defect occurrence and defect size may be only partially known until remedial testing or distress becomes necessary [27]. Li et al. [27] further note that such uncertainty can lead to delays, remedial action, higher inspection cost, and disputes over cause and responsibility. Helical piles, on the other hand, offer an advantage in this respect because installation generates pile-by-pile torque and depth data, and the torque–capacity relationship has been validated against field records and full-scale load tests.

Accordingly, for transmission and renewable-energy projects, a helical pile solution can be argued to reduce exposure to latent-condition risk in two ways: first, by reducing dependence on excavation stability, slurry control, and concrete placement in variable ground; and second, by transforming part of the subsurface uncertainty into measurable installation parameters that can be reviewed immediately by the contractor, designer, superintendent, and certifier [27,28].

Considering all of the above, geotechnical investigation programs for transmission line structure foundations face distinct scheduling and site-access challenges relative to other infrastructure types. Such investigations are typically mobilized as early, standalone works well ahead of main construction, with their timing sensitive to site access, weather conditions, and the sequencing of formal planning approvals. Foundation systems that reduce dependence on long-lead site establishment, extensive concrete logistics, and weather-sensitive curing windows (while minimizing site labor hours, specialist trade stacking, and logistics and QA/QC complexity) can therefore improve program certainty, particularly where early works must transition rapidly into construction without remobilization or rework. In this regard, helical pile groups can be positioned not only as a geotechnical solution but also as a procurement and schedule-risk mitigation measure in regulated transmission programs facing concurrent approval gating and workforce constraints.

1.2. Australian Soil Profiles and Geotechnical Implications

Australia’s vast and ancient geological landscape presents a unique set of challenges for infrastructure development. The continent’s geology is composed of Archaean cratonic shields, Proterozoic fold belts, and Phanerozoic sedimentary basins [29]. While this diversity results in a wide range of soil types, certain profiles are particularly problematic for deep foundations and are highly prevalent along major transmission corridors.

One of the most significant and widespread challenges is the presence of reactive or expansive clay soils, which are characterized by their high clay content and ability to absorb and shed water [30]. This process leads to dramatic and cyclical shrink-swell behavior, a phenomenon often visible in the dry season as deep polygonal cracks in the ground. This constant movement exerts immense pressure on foundations, leading to differential heaving or settlement that can cause severe structural distress [31,32]. For lightly loaded structures, such as transmission tower legs, the uplift forces exerted by swelling clays can be substantial, as they may not have enough dead weight to counteract the upward pressure [33].

Traditional shallow foundations are particularly vulnerable to this behavior, but even some deep foundation methods can be compromised. Bored piles, for example, can be engaged by friction within the reactive clay zone, causing them to follow the same path and level of heave movement, leading to structural damage. This has been observed to cause significant distress, including cracked slabs and floors [34].

Another major challenge is the presence of low-bearing-pressure soil, such as loose sands, which are common in coastal regions and inland arid areas. These soils have poor load-bearing capacity and can present significant risks for foundation stability [30]. Urban and developing areas are also often built on uncontrolled fill or alluvial soil, which is weak and unconsolidated, placing standard shallow footings at high risk of shifting or sinking [35].

Shallow groundwater is also costly and problematic for the application of traditional bored piles. The excavation process creates an open hole where water can freely flow in from the surrounding soil. This influx of water causes the sides of the hole to slump or cave in (especially in sandy or silty soils), destabilizing the excavation. To proceed, contractors must implement complex and expensive mitigation measures such as: installing temporary steel casings, using drilling mud (bentonite slurry) to create hydrostatic pressure, or constantly running dewatering pumps. All of this slows installation, increases cost, and can compromise the quality of the concrete pour [36].

Another geotechnically important profile in Australia is the deep weathered bedrock sequence, particularly saprolite, which is common in landscapes shaped by prolonged chemical weathering. Australian regolith studies show that weathered rock, sediment, and soil cover occur over large parts of the continent, and that saprolite profiles are widespread in these terrains [37,38]. In Western Australia, for example, complete weathering profiles developed on granite commonly include soil, duricrust, saprolite, and saprock, with typical profile thicknesses of the order of 20 m in the Darling Range [39]. Australian and international residual-soil studies further show that these profiles are not mechanically uniform: weathering produces strong vertical changes in texture, pore structure, permeability, and shear strength, and the transitions between horizons are frequently gradational rather than sharply bounded [40,41]. For transmission foundations, this has a direct design consequence: a borehole may identify a broad weathered interval, but not the precise depth at which reliable end bearing or socket resistance develops. That depth can vary considerably even over short horizontal distances [37,40,41].

This has direct implications for bored pile constructability. In saprolitic and highly weathered profiles, the pile bore can encounter mixed behavior over short depth intervals, including softened clay-rich seams, relict rock fabric, variable cementation, and irregular transitions into saprock or weak rock. Such variability complicates drilling control, socket termination, sidewall stability, and base cleaning, and can increase reliance on casing, slurry support, and conservative construction tolerances [40,41]. The consequence is not only slower installation, but also a greater requirement for post-construction verification because bored-pile performance is sensitive to construction-induced defects such as toe debris, mud cake, necking, and bulging [27,42]. Li et al. note that, in practice, only a limited proportion of bored piles can usually be inspected because full integrity assessment is costly and can delay work [27]. More recent reliability analysis indicates that defects associated with bored-pile construction can materially reduce ultimate capacity; in the cited study, toe debris reduced capacity by about 17% and mud-cake defects by about 19% [42].

Accordingly, where deep saprolite is present, bored piles remain feasible but are often less constructible and less predictable than in more uniform strata, because the weathered profile amplifies uncertainty in founding level, bore stability, and as-built pile quality [27,40,41,42]. Table 1 summarizes major REZ (Renewable Energy Zone) corridors and the dominant soil challenges along them in Australia.

Table 1. Major REZ corridors and the dominant soil challenges along them.

REZ/Transmission Corridor	Region/State	Primary Stated Purpose/Driver	Inferred Dominant Soil Challenges for Foundations
Central-West Orana (CWO)	Central-West NSW	New South Wales’ first planned REZ, focusing on solar and wind generation.	Mixed/weathered sediments and rock: expected shallow to moderately deep weathered sandstone and shale. Potential for variable rock depth, requiring careful helix placement. Expansive clays in areas could pose issues with lateral soil movement [43].
HumeLink (HCC)	Southern NSW/ACT	New transmission to connect Snowy 2.0 and deliver renewable energy from the region.	Mountainous and rugged terrain: likely encounters shallow bedrock and rock outcrops, making deep pile penetration difficult. Colluvial soils (slope deposits) can be loose and unstable on steeper terrain [44].
Victoria to New South Wales Interconnector West (VNI West)	Victoria/NSW border	Major interstate link to share renewable energy capacity.	Riverine plains and volcanic plains: deep alluvial sequences (clays, silts, sands) near major rivers (Murray, Murrumbidgee) may include soft, compressible layers. Basalt-derived soils in this region are known to be highly variable in depth and strength, with reactive clay behavior (shrink-swell movement) and stony, boulder-affected profiles typical of the Newer Volcanics geological formation [45].
Marinus Link	Tasmania/Victoria (Bass Strait)	Undersea HVDC links to export Tasmanian hydro and wind power.	Coastal and marine environments (onshore components): foundations near coastlines may encounter soft marine clays, liquefiable sands in seismic zones, and highly corrosive soil conditions requiring specialized steel protection [46].
Queensland Renewable Energy Zones (QREZ)	Central and Southern QLD	Multiple zones harnessing solar and wind. Central QLD focuses on Gladstone/Isaac region.	Highly variable geology: can range from deep alluvial floodplains (soft soils) to residual soils over hard rock (e.g., basalt, granite) [47].

1.3. Review Scope and Methodology

This review follows a narrative (non-systematic) methodology appropriate to a technology-comparison and practice-guidance review of helical versus bored pile foundations, rather than a PRISMA-style systematic review. The literature was identified primarily through Scopus, Web of Science, and Google Scholar, using combinations of the keywords ‘helical pile’, ‘screw pile’, ‘transmission tower foundation’, ‘bored pile’, ‘drilled shaft’, ‘torque correlation factor’, ‘pile life-cycle cost’, and ‘tower grounding/earthing’, supplemented by forward and backward citation searching from key standards and reference texts. No fixed lower date bound was applied to core geotechnical references, reflecting the field’s reliance on foundational studies dating to the late 1980s; searches for Australian regulatory, market, and case-study material were concentrated on 2018–2026 sources to capture the current transmission investment and procurement context. In total, approximately 300 sources were reviewed, spanning peer-reviewed journal and conference papers, national and international standards, government and council publications, industry case studies, and company websites, product literature, and technical blogs; of these, 129 are cited in the final reference list. Peer-reviewed journal articles and formal standards or regulatory publications were treated as the primary evidentiary basis for technical and performance claims and account for the majority of the sources retained; company, product, and trade/blog sources were included only where they supplied project-specific operational data not available in the peer-reviewed literature (e.g., achieved pile counts and installation rates for named projects), and are identified as such at the point of citation.

This review aims to critically evaluate helical piles as a conditional alternative to conventional bored pile foundations for Australian transmission and renewable-energy infrastructure. It examines the two systems’ comparative geotechnical and structural performance, installation logistics and delivery risk, life-cycle cost, environmental impacts, and the effect of foundation type on electrical grounding and lightning performance. Rather than establishing a general case for either technology, the review synthesizes current evidence to identify the ground conditions, structural demands, and project constraints under which helical piles offer a genuine advantage over bored piles, and those under which bored or hybrid solutions remain preferable.

2. Helical Piles

Helical piles provide a solution that is fundamentally designed to overcome the challenges of traditional foundations. The technology bypasses unstable surface layers, anchoring the structure in deeper, stable ground or bedrock below the zone of seasonal moisture fluctuations [48]. This design philosophy directly addresses the root cause of foundation distress in reactive clays by eliminating the interaction between the primary load-bearing elements and the problematic soil layer. This approach provides a level of certainty and long-term stability that traditional shallow foundations and even some deep foundations cannot guarantee, making it a particularly suitable solution for critical infrastructure in Australia’s diverse and challenging geotechnical landscape. Unlike that of bored piles, the installation of helical piles is largely unaffected by shallow groundwater. This is because the pile is torqued directly into the ground without pre-excavation. Helical piles can withstand tensile forces from structural uplift and overturning. They also reduce exposure to latent-condition risk. Consequently, they are considered a viable substitute for driven piles in offshore settings, as their helical plates act as anchors, providing significant uplift resistance [49].

Many researchers have outlined the benefits of helical piles, which include rapid, vibration-free installation to various depths using extension segments. A 10 m pile, for example, can be installed in minutes by a small crew, making helical piles excellent for restricted sites and built-up areas. A primary limitation, however, is their incompatibility with very hard, dense, or gravelly soils, as these can damage the helical plates or cause installation deflection [50].

2.1. Helical Pile Anatomy and Load Paths

A helical pile is a deep foundation element composed of a central steel shaft and one or more helical bearing plates welded to it [51]. Typical dimensions vary considerably with application and required capacity. Standard shaft sizes include 1.5-inch and 1.75-inch square shafts and round shafts ranging from 3.5 inches up to 10.75 inches in diameter, with many common helical piles using an average helix diameter of around 12 inches, though heavily loaded structures may require substantially larger helices [52]. The pitch of each helix (the axial distance the plate advances per full rotation) is a tightly controlled parameter: acceptance criteria specify a pitch of 3 inches, plus or minus a quarter inch, with all helices on a multi-helix pile sharing the same pitch so that each successive plate tracks the path cut by the one ahead of it [53]. On multi-helix piles, plate diameter increases progressively from the leading (bottom) helix upward, so that each plate advances into soil not yet disturbed by the plate above it [53]. Overall pile length is achieved through bolted or welded shaft extensions and can range from a few meters for lightly loaded structures to over ten meters where a deep, competent bearing stratum must be reached [54]. Figure 4 shows a schematic of a helical pile.

Figure 4. Schematic of a helical pile.

These piles are screwed into the ground by applying both torque and axial (crowd) force, typically delivered through a hydraulically powered rotary drive unit [55]. The shaft’s primary functions are to provide sufficient torque capacity during installation and to transfer the structural loads to the helices after installation [56]. The helices function as the primary load-bearing elements, providing resistance in both compression and tension by transferring load to the soil through end-bearing pressure. The modular design, which allows for the addition of extensions via bolted or welded connections, enables the pile to be advanced to the required depth to reach a specified load-bearing stratum [57]. Figure 5 shows the stages of helical pile installation, as the pile penetrates the ground into deeper layers.

Figure 5. Stages of helical pile installation (adapted from Huang et al.) [58].

Helical pile installation compacts and pushes soil radially outward as the pile advances, densifying the ground immediately around the pile, or shears and removes a small core of soil ahead of the pile, minimizing disturbance to the surrounding ground. This distinction has a direct bearing on both installation behavior and the resulting soil conditions around the finished pile [59].

2.2. Application of Helical Piles

Helical pile foundation systems were first used for constructing the Wyre and Maplin Sands lighthouses in shallow waters [60]. Technological advancements are driving the increasing adoption of helical piles in the foundations of new construction projects. The Kempe Children’s Center in Denver, Colorado (1997), illustrates how grouped helical piles can carry heavy column loads. Its foundation used 105 vertically installed piles for axial support and 17 battered piles for lateral resistance. Individual piles were rated at 445 kN, so three were placed beneath every reinforced concrete column (roughly 1335 kN of combined capacity against a 667 kN demand, a safety factor of about 2) [61]. A hospitality and conference complex in Windsor, Ontario, finished in 2007, faced a persistent problem from its riverside setting: closeness to the Detroit River kept the local water table high, and that groundwater pushed up against the foundation with real buoyancy force. To hold the structure down against this uplift, engineers installed 259 helical piles with square steel shafts, each 57.1 mm across, then wrapped every shaft in a 152 mm grout casing, sized to withstand 444 to 734 kN of tension [62].

Nowadays, helical piles are increasingly being adopted for bridge retrofitting, with the Multi-Helix Micropile (MH-MP) method standing out as a particularly fast and cost-effective technique. Several bridges have been successfully retrofitted using this method. For example, following an earthquake in 2011, several piles of the Yokohama Bridge in Japan were severely damaged and required immediate retrofitting. The MH-MP method was selected as the most effective technique for pile reinforcement [63].

Helical piles can also be used as wind turbine foundations. For instance, remote village sites in Alaska pose a foundation challenge that Kasigluk illustrates well: when three turbines went up there in 2006, difficult ground conditions and near-nonexistent road access ruled out most conventional options, leaving helical piles as the practical choice. Engineers sized the piles to counter roughly 100 kips of uplift, specifying a 20-inch shaft fitted with a pair of 36-inch helices and driven to depths in the 36-to-40-foot range. Once operating, the turbines produced about 415,500 kWh annually (enough to cut local electricity demand by a fifth to a quarter). That track record is why Alaska’s village-scale utility, AVEC (Alaska Village Electric Cooperative), now has plans on the books for another 17 to 21 turbines across additional villages within the next three to five years [64].

The diverse practical projects discussed above show that helical piles can be successfully used in the construction of new buildings, rehabilitation of old buildings, retrofitting of bridges, etc. The confidence of contractors and the public increases as the number of successful projects increases. Helical piles can also be used as a foundation in solar farms, billboards, transmission towers, and wind turbines [50]. Helical piles are not limited to onshore structures and can also be used for offshore applications such as offshore wind turbine foundations [51]. Centrifuge modeling by Ullah et al. [56] demonstrates that helical piles can develop significant vertical tensile (uplift) capacity, supporting their consideration as offshore foundations. Relative to driven piles, helical pile installation avoids the significant acoustic emissions associated with pile driving, emissions that can be detrimental to marine species reliant on sound for foraging, orientation, and communication. Figure 6 shows a schematic of helical piles used as foundations for offshore wind turbines.

Figure 6. Schematic of helical piles used as foundations for offshore wind turbines (adapted from Safdar et al.) [50].

2.3. Advantages of Helical Piles over Traditional Foundations

Helical piles offer a compelling solution for the logistical and productivity challenges of remote Australian transmission projects. Their installation process is significantly faster and more efficient than traditional methods, resulting in substantial savings in time, labor, and equipment [58].

2.3.1. Remote Constructability and Installation Process

The installation of helical piles is a low-impact process that requires minimal excavation and no soil removal, as the pile displaces the soil sideways as it screws into the ground [65]. This eliminates the need for large-scale digging and the associated costs and complexities of handling and disposing of soil spoil [66]. The process of installing helical piles is largely silent and does not transmit ground vibration, an advantage that makes them particularly suited to projects in remote or ecologically sensitive locations, as well as urban sites where access is constrained [48].

A helical pile advances into the soil as mechanical torque, applied at the top of the shaft, rotates the pile downward to depth [54]. This use of readily available, often smaller equipment simplifies site access and reduces the logistical costs of mobilizing heavy, specialized rigs to remote locations [7]. The installation process is not affected by weather conditions, a major advantage in Australia’s diverse climate, as piles can be installed in wet, dry, or mixed conditions without delays. Unlike bored piles, which often stop during rain events due to soil handling and mud conditions and require vast amounts of water, helical piles are totally independent of weather conditions, and they need no water for installation [66].

A further constructability advantage of helical piles is the elimination of the curing-and-release hold point that is inherent to cast-in-place concrete foundations. In concrete practice, 28 days remain the standard reference age for specified compressive strength, while even conventional structural curing guidance commonly assumes at least 7 days of initial moist curing for ordinary structural concrete [67]. For bored pile and tower foundation works, this material behavior translates into a program constraint because erection and subsequent loading are typically governed by strength gain and release criteria rather than excavation completion alone. Peer-reviewed work on concrete piles likewise shows that the common assumption that piles are ready for integrity testing after 7 days is not universally reliable. Niederleithinger and Taffe reported that defect detection may be possible after a few days but is more reliable after about 10 days, confirming that concrete foundations introduce a non-trivial waiting period even before the next activity can proceed [68]. By contrast, field testing of helical piles in cohesive soil has shown that piles can be evaluated immediately after installation, and that installation-induced pore-pressure effects had little influence on short-term ultimate capacity, supporting the practical observation that helical piles can transition directly to the next construction stage without a curing hold point [69]. For transmission towers, the resulting schedule benefit can therefore be reasonably expressed as up to 28–35 days removed from the critical path, particularly when the full release sequence is considered, including curing, strength verification, inspection sign-off, and readiness for tower erection and subsequent stringing activities.

The consequence of this time saving is impressive. Pile-construction research has shown that cycle time, productivity, and cost are tightly coupled, and that pile works should be analyzed as a combined time–cost process rather than as a purely material quantity problem [70,71]. In practical EPC terms, eliminating the 28–35-day foundation release window reduces the time-related preliminaries tied to it: supervision, access-road maintenance, traffic management, equipment standby, remobilization risk, and exposure to rain or groundwater-related delays at partially completed sites. Assigning a single dollar value to this saving would require project-specific cost data that is not available here; a more rigorous approach instead expresses it in terms of the site’s own daily indirect cost. For a tower site with daily indirect cost C_day, the avoided time-related cost is approximately

ΔC_time ≈ C_day × (28–35 days)

(1)

Beyond this direct cost avoidance, removing the curing wait also allows tower erection to proceed as a continuous install-and-progress workflow, rather than a stop–start sequence gated by concrete strength gain. This framing is more defensible than asserting a fixed saving per foundation, yet still conveys the central point: eliminating the curing requirement is both a schedule and a commercial advantage [70,71].

2.3.2. Productivity Metrics

The productivity of helical pile installation is a key differentiator. A small crew of one to two people per rig can be used [50]. Industry data suggest that roughly 31 helical screw piles can be installed per day with a standard crew and machinery [61]. This speed reduces project timelines, with foundations for large projects often completed in a matter of weeks, in stark contrast to the month-long process required for traditional methods [72].

Moreover, repeatable prefabrication (factory-first philosophy) accelerates the on-site installation process. Once installed, helical piles have immediate load-bearing capacity, allowing the next construction phase, such as tower erection, to begin immediately [33]. This directly reduces project delays and allows for a more streamlined, just-in-time construction workflow.

2.3.3. Quality Assurance and Quality Control (QA/QC)

The QA/QC process for helical piles is a critical advantage. Unlike traditional deep foundations, which rely on geotechnical reports that can only provide an estimated capacity, helical pile capacity can be verified in real time during installation [61]. The most widely used method for on-site verification is the torque correlation method, which relies on the empirical relationship between the ultimate pile capacity (Q_u) and the final installation torque (T). This is expressed by the formula Q_u = K_t ×T, where K_t is an empirically derived torque correlation factor. This provides a continuous, real-time readout of soil strength and pile capacity during installation, allowing the operator to verify that the required capacity has been achieved [73].

Under AS 2159-2009, load testing is not universally mandated. It is required only where a basic geotechnical strength reduction factor above 0.4 is adopted and the average risk rating is 2.5 or greater, and the standard otherwise encourages it by permitting a higher reduction factor as more piles are tested. For helical piles, torque–capacity correlations must be supported by static load tests on the site or in similar ground. Load tests verify the tested piles and the design assumptions, not every installed pile, so installation records of final depth and torque are used to check the untested production piles against the verified correlation. The supervising engineer plays a key role in reviewing detailed installation logs that document the final depth and torque of each pile, ensuring compliance with Australian standards and the design plan [74].

The productivity and QA/QC advantages of helical piles represent a strategic risk-mitigation measure for large-scale, remote projects. In a market facing significant workforce and logistical challenges, a foundation system that requires less manpower, less specialized equipment, and less material transport directly reduce project risk and cost exposure.

2.4. Design and Performance of Helical Piles

The performance and durability of helical piles are critical factors for long-term infrastructure projects and depend on many variables, including soil stiffness, soil moisture, the material of helical piles, pile geometry, and pile head fixity [75,76].

Helical piles are manufactured from high-grade steel, such as grade C350 or ASTM A500 Grade C, and are protected from corrosion, typically through hot-dip galvanization [53,77]. Studies on steel piles with decades of service show that the corrosion rate is negligible for most of the piles, as they are embedded in undisturbed, oxygen-deficient soil. Protection is most critical for the portion of the shaft near the ground line, where increased oxygen availability poses a higher risk of corrosion. Hot-dip galvanization or epoxy coatings are commonly used to mitigate this risk [78].

AS 2159-2009 (Australian Standard for Piling Design and Installation) provides a structured, risk-based framework for determining the appropriate level of corrosion protection for steel piles, including helical piles. Its purpose is to guide engineers in selecting a protection method that matches the aggressiveness of the site environment, ensuring the pile’s long-term durability [74]. Tables 6.5.2(A) and 6.5.2(B) (included in Piling—Design and Installation Standard [74]) define the site’s corrosive aggressiveness. These tables are used together to classify the site environment. In effect, this provides a corrosion-risk classification for the ground. Once the site’s aggressiveness class is determined from the tables above, Table 6.5.3 (included in Piling—Design and Installation Standard [74]) can be used to find the required protection. For each aggressiveness class (negligible to very high), it lists acceptable methods, which generally involve a combination of steel thickness, protective coatings, and cathodic protection [74].

Among the factors influencing helical pile durability, the design parameters are the ones an engineer can actively control, since they can be adjusted through the design process. The properties of the surrounding soil, by contrast, are fixed by the characteristics of the project site and cannot be altered. Performance depends on the interaction between the two, rather than one factor dominating the other [75].

The performance of a helical pile is highly dependent on its geometry. Industry standards dictate a uniform pitch for the helices, typically 3 inches per 360-degree rotation. This ensures that each helix tracks through the same continuous helical groove cut into the soil, minimizing disturbance and preserving soil strength [53]. This contrasts with piles of variable geometry that behave more like an auger, which can cause significant soil disturbance and compromise the pile’s ultimate capacity [79]. The helical plates are arranged on the shaft such that their diameters either remain the same or increase as they get farther from the pilot point, ensuring efficient advancement [53]. However, a study by Mamdouh Nasr proves that even helical piles may suffer from soil loosening. This study argues that the common way helical piles are designed is flawed because it only focuses on whether the pile can hold the ultimate load without breaking. It ignores the critical issue of how much the pile will settle under normal, everyday loads. The authors used a real-world case study of a helical pile installed in very dense sand. The installation required extremely high torque, which stirred up and loosened the dense sand around the pile (a process known as dilation). When the pile was load-tested, it had enough ultimate strength, but it performed poorly under its intended working load. It settled (moved downward) much more than expected because the loosened sand particles were re-compacting under the load [80].

The study concluded that even though standard design formulas correctly predicted the pile’s ultimate failure load, they completely failed to predict the large and problematic settlement at normal service loads. The high-force installation process permanently alters the soil around the pile, and this must be considered in the design. Ignoring this leads to poor performance. To predict settlement and account for complex soil behavior (such as dilation in dense sand), engineers should use advanced tools such as finite element modeling instead of relying solely on simple, outdated formulas [80]. There are some other factors that should be considered while designing a helical pile.

2.4.1. Fatigue and Dynamic Load Considerations

A critical design concern about helical piles is that these piles frequently experience cyclic loading, which can progressively degrade their capacity and lead to failure. Therefore, understanding their tensile performance under repeated loading is essential.

Cyclic loading regimes are typically distinguished along two axes. The first is direction: loading is either one-way, meaning purely compressive or purely tensile, or two-way, alternating between the two. The second is the rate of application, which separates static, quasi-static, and dynamic behavior. Quasi-static cycling occurs slowly enough that inertial effects are negligible, whereas dynamic cycling brings those inertial forces into play. Researchers typically probe these effects by running controlled sequences of loading and unloading at fixed frequencies and amplitudes, and the resulting pile response depends on how the average load (Q_avg) and cyclic amplitude (Q_cyc) combine to place the system in a stable, metastable, or unstable regime. Within the stable range, low-frequency cycling has in some cases been shown to increase capacity by as much as 20%, rather than degrade it. Because of this, a substantial body of work has focused specifically on how cyclic loading shapes helical pile performance [81]. Many researchers have tried to understand the relationship between cyclic loading and helical pile performance. For example, Cerato and Victor [82] determined that the repeated application of cyclic loads can enhance a helical pile’s ultimate tensile capacity while also mitigating long-term creep. They attribute this improvement to progressive soil densification directly above the helical plate, a mechanism activated by the repetitive loading process. Beyond capacity considerations, cyclic tensile loading induces a repetitive uplift motion that can generate voids beneath the helical plate. Schiavon [83] noted that these voids are particularly pronounced under conditions of high cyclic load amplitude or in low-density soil zones. Complementing this, Costa [84] demonstrated that greater load amplitudes and higher mean loads diminish both the stability and the overall stiffness of the pile–soil system. Although helical piles are seeing growing application in foundation engineering, a significant research gap persists regarding their behavior, most notably their performance under cyclic loading. Thus, more precise investigations and modeling techniques are required to evaluate the performance of helical piles under cyclic loading.

2.4.2. Lateral Capacity Behavior of Helical Piles

The lateral capacity of a helical pile refers to its ability to resist horizontal loads (e.g., from wind, seismic activity, earth pressure, or machinery) applied perpendicular to its shaft. Unlike tension and compression, which are resisted primarily by the helices, lateral load is resisted almost entirely by the passive pressure of the soil acting against the embedded shaft and helices. In essence, the lateral capacity behavior of a helical pile is governed by the bending resistance of its shaft and the strength/stiffness of the surrounding soil. While the helices are critical for axial loads, they play a secondary role in lateral resistance. Design, therefore, shifts focus from helix configuration to shaft geometry and soil–structure interaction analysis to ensure the pile can resist horizontal forces without excessive deflection or structural failure [53,85].

Shaft geometry is a key structural parameter governing lateral capacity, with circular (pipe) shafts generally offering greater bending stiffness and lateral resistance than square shafts of comparable size, due to their larger section properties [52]. Wall thickness and material grade set the structural limits against yielding and buckling [53].

Lateral capacity is governed jointly by soil properties and shaft design. Soil stiffness and strength are fundamental: dense sands and stiff clays provide a substantially higher modulus of subgrade reaction than loose sands or soft clays [85]. Capacity can be enhanced through larger shaft diameter and wall thickness, battered installation (converting lateral loads into axial tension/compression pairs), fixed-head pile–cap connections, and post-installation grouting to enlarge the effective shaft diameter and stiffen the surrounding soil [61,86].

Even with battered piles, fixed-head connections, and large-diameter shafts, there is a practical economic and geometric limit to the lateral capacity of a single helical pile or a small group. For structures imposing exceptionally high lateral shear or overturning moments, such as tall signboards, cantilevered retaining walls, large bridge abutments, or the legs of heavy industrial equipment, the required shaft diameter or batter angle may become impractical. In these cases, a reinforced concrete pile cap integrated with ground beams or a structural grillage is essential to distribute the massive lateral loads across multiple piles and engage deeper, more competent soil layers for passive resistance [87].

2.5. Installation Failure Modes of Helical Piles and Mitigation Strategies

The main risks affecting helical pile installation are premature refusal, where hard or dense strata prevent the pile from reaching its design depth or damage the helical plate [51], and loss of proper pitch advancement, where the pile begins to auger rather than displace the soil, degrading the reliability of the torque–capacity correlation and reducing ultimate capacity by as much as two-thirds in extreme cases [79]. These issues typically arise from a mismatch between the installation equipment, pile design, and actual site conditions. Table 2 summarizes each failure mode’s causes, consequences, and key mitigation strategies.

Table 2. Failure modes of helical piles: causes, consequences, and key mitigation strategies.

Failure Mode	Primary Causes	Consequence If Unchecked	Key Mitigation Strategies
Premature refusal	Obstructions (rock, debris), denser-than-expected soil (e.g., hard till), undersized installation equipment [51].	Pile fails to reach load-bearing stratum, resulting in inadequate capacity [51].	Use larger, more capable equipment (e.g., excavator over skid-steer); perform pre-installation site investigation; pre-drill through obstructions [53].
Loss of pitch/augering	Insufficient downward axial force from equipment; high-torque, low-penetration installation [79].	Soil is excessively disturbed torque–capacity correlation is invalid, leading to reduced capacity [79].	Use equipment with adequate breakout force and weight; monitor rate of penetration (aim for 2.5–3 inches per revolution) [53].
Shaft buckling (during installation)	Installing in very soft/loose soils with slender square shafts; lack of lateral soil support [85].	Structural damage to the pile, making it unfit for service [85].	Switch shaft type: use pipe shafts, combo piles, or grouted micropiles in soft soils [85].

2.6. Practical Deployment Limits of Helical Piles

Helical piles are generally unsuitable where competent bedrock lies at shallow depth, since the system cannot achieve sufficient embedment for stability, and are similarly ill-advised in dense, abrasive soils such as river gravels, where high installation torque can lead to premature refusal or damage to the helical plate [51]. Sites with subsurface obstructions such as boulders carry a comparable risk, as these can deflect the pile off course during installation [51], and such conditions warrant thorough pre-installation investigation before helical piles are selected as the foundation solution.

Decision Guidance: Site Conditions Favoring Bored Piles

The limitations discussed in Section 2.4, Section 2.5 and Section 2.6 indicate that helical piles are not a universal substitute for bored piles. The choice between the two should be treated as a site-specific geotechnical and structural decision, informed by the indicative conditions summarized in Table 3.

Table 3. Conditions under which bored piles or alternative foundation systems may be preferred over helical piles.

Condition	Why Helical Piles Are Disadvantaged	Preferred Alternative
Competent bedrock within approximately 1 m of the surface	Insufficient embedment depth for helix bearing and uplift resistance	Bored pile socketed into rock, or spread footing on rock
Dense gravels, cobbles, or boulder-affected ground	High risk of premature refusal, helix/shaft damage, or deflection off course	Bored pile with casing/slurry support, or driven pile
Very high lateral shear or overturning demand at a single leg (e.g., dead-end/angle towers) beyond practical batter or shaft-diameter limits	Uneconomical shaft diameter or batter angle required	Reinforced concrete pile cap with grillage engaging multiple piles, or larger-diameter bored pile
Very dense sand where high installation torque induces dilation/soil loosening	Ultimate capacity may be adequate, but service-load settlement can exceed acceptable limits (Section 2.4)	Bored pile, or helical pile design verified by finite element modeling rather than closed-form torque correlation alone
Foundation required to perform as the primary tower-earthing electrode with a well-precedented grounding-resistance calculation	Helical pile grounding performance not yet independently verified (Section 2.8)	Concrete/bored foundation, or a helical pile supplemented with a purpose-designed grounding electrode/counterpoise

Many of these conditions can be screened using routine desktop geological mapping and a limited targeted site investigation, allowing the foundation-type decision to be made at an early stage rather than discovered during construction. This condition-driven selection process is not unique to Australia. Alrowaimi [88] describes an equivalent evaluation of driven versus helical pile options for a 100 MW solar power plant in Michigan, USA, where weak and compressible near-surface soils below approximately 1.5 m depth made the otherwise more economical driven-pile option unfavorable, prompting the adoption of helical piles instead.

2.7. Grouped Pile Performance for Tower Legs

Transmission towers, which require a foundation system capable of resisting significant compressive, tensile, and lateral loads, often utilize a group of piles at each leg [2,87]. The behavior of closely spaced pile groups is a critical design consideration, as the interaction between adjacent piles can reduce their overall performance. However, research indicates that the unique geometry of helical piles fundamentally alters pile group mechanics, resulting in more predictable and often superior performance compared to conventional pile groups at equal spacing [87]. This is primarily due to the helical pile’s slender shaft diameter, which is significantly smaller than its helix diameter. This geometry localizes soil displacement around the helices and reduces the stress and strain fields between adjacent piles, minimizing shaft-to-shaft interaction [87]. The failure mode for helical pile groups is typically individual bearing failure of each pile, rather than the less efficient block failure that can occur with closely spaced conventional piles [89]. This means that for a given load requirement, a helical pile group may require fewer piles or smaller spacing, which has direct cost and time implications for a project.

Group efficiency in helical pile foundations depends strongly on center-to-center spacing, with adjacent piles’ stress zones overlapping more, and group efficiency dropping further, as spacing decreases. Lanyi-Bennett and Deng (2019) [89] measured group efficiencies of 90.7%, 95.5% and 96.8% at spacing ratios of 2D, 3D and 5D, respectively, in a full-scale field study, confirming that even at 3D spacing some reduction in group performance relative to the sum of individual pile capacities should be expected. This makes spacing a critical design consideration for foundations supporting heavy structures such as transmission towers, where excessive settlement from group interaction is a key risk. They also indicated that while the effects of installation-induced excess pore pressure significantly reduce the performance of groups in cohesive soils, these effects are limited to the soil near the pile shaft for single piles and do not affect their ultimate state capacity [89]. Figure 7 shows a schematic of grouped helical piles [90].

Figure 7. Schematic of grouped helical piles (concept adapted from Venkatesan et al.) [90].

For structures resisting significant lateral loads, such as diagonal-legged transmission towers, helical piles can be installed at a batter angle matching the leg geometry as an alternative to relying on passive lateral soil resistance. Battering aligns the pile more closely with the dominant force path from the leg, allowing the foundation to draw more on the helical pile’s axial strength rather than its comparatively limited lateral capacity [85].

2.8. Electrical Grounding and Earthing Considerations

Tower foundations carry structural loads and form part of the transmission line’s earthing system, with direct implications for personnel safety and lightning performance. During a power-frequency fault, current dissipated through the structure footing produces an earth potential rise, and the resulting step and touch voltages must be managed to acceptable levels [91]. During a lightning strike, the tower footing impedance governs the voltage developed across line insulation and hence the likelihood of back-flashover [92].

Beyond personnel safety, tower footing resistance is also a first-order variable in a line’s lightning performance. Christodoulou et al. [93] show that back-flashover failure (one of the principal causes of lightning-related transmission line outages) is governed directly by tower footing resistance, alongside insulation level and surge arrester design, within an optimization framework applied to six operating 150 kV transmission lines. Their method achieved lightning failure rate reductions of 70–95% through combined adjustment of these parameters, demonstrating that foundation grounding performance is not merely a compliance item but a measurable driver of line reliability and life-cycle failure cost.

Concrete tower foundations are well documented in the electrical engineering literature as functioning as “natural” grounding electrodes. In fact, their embedded reinforcing steel, combined with concrete’s large surface area in contact with soil, provides a usable current dissipation path. Moreover, established methods exist for calculating both power-frequency and lightning-impulse grounding resistance for such foundations [94].

Whether a steel helical pile foundation would perform comparably remains an open question that the current literature has not directly addressed. Analogous work on solid steel pole foundations, however, offers a relevant precedent: computed grounding resistance for coated steel poles was found to be equal to or better than that of concrete piles under representative conditions [95], suggesting that the trade-off between a helical pile’s smaller soil-contact area and steel’s superior conductivity is a legitimate engineering question rather than a presumed disadvantage. No published research to date has examined helical pile foundations specifically as grounding electrodes for transmission structures; given that footing resistance affects both safety margins and lightning failure rates, this represents an important direction for future investigation.

3. Case Snapshots and Comparative Metrics

While traditional methods such as bored concrete piles have historically been the default for major transmission projects, recent Australian case studies in the renewable energy sector demonstrate the clear advantages of helical piles.

3.1. Limondale BESS: Design, Verification, and Construction Performance

The Limondale battery energy storage system (BESS) project in New South Wales provides a large-scale Australian case study of helical piles for energy infrastructure. The foundation package comprised 864 piles supporting 144 battery units, with six piles per unit and a nominal 60-day foundation program [96]. Three constraints governed the foundation selection. The first was serviceability: differential settlement across each battery unit group was limited to 12.5 mm, a tolerance set by the equipment rather than by the structure. The second was geometric: a horizontal positional tolerance of 75 mm was absorbed within the pile-to-cap connection design rather than by setting-out precision, which materially affects achievable installation rates. The third, and in practice the decisive one, was logistical: with no batch plant within economic reach, any cast-in-place scheme carried a concrete supply chain of several hundred kilometers, while a prefabricated steel scheme carried only the freight of the piles themselves.

Site investigation included 15 boreholes and 54 field tests, indicating predominantly very stiff to hard sandy and silty clay beneath an engineered surface layer, with no rock or major subsurface obstructions identified within the founding depth. These conditions were generally favorable for helical piling, although test installation demonstrated that pile geometry remained critical.

The initial design used an approximately 140 mm shaft with a 500 mm helix. During test piling, installation resistance increased rapidly, and the pile terminated at approximately 3.8 m before achieving the preferred embedment below the seasonal moisture-variation zone. The production design was consequently modified to a 350 mm helix, allowing greater penetration while maintaining the required capacity through increased embedment and installation verification. This illustrates an important characteristic of helical foundations: helix enlargement may increase bearing capacity but also increase installation torque and can therefore limit achievable depth [97]. Three static compression tests on the original trial configuration reached the 150 kN working load with a maximum measured displacement of 3.56 mm, substantially below the specified 12.5 mm serviceability limit. As these tests preceded the geometry change, they demonstrate favorable ground response but should not be interpreted as direct verification of the final production configuration.

Verification of the as-built foundation was instead undertaken through installation monitoring of all 864 production piles. Final installation pressure ranged from 110 to 390 bar, with a median of 180 bar, compared with an acceptance criterion of 54 bar associated with the adopted torque–capacity relationship. All piles exceeded the acceptance threshold. Final embedment ranged from 2.8 to 4.0 m, with a median of 3.6 m, while 848 of 864 piles were installed within the specified positional tolerance. These results demonstrate the practical value of pile-by-pile installation records as a QA/QC tool and illustrate the degree of spatial variability that may occur even within an apparently consistent ground profile.

Construction productivity averaged approximately 40–50 piles per day [96], following a shallow pre-drilling operation through the engineered surface layer. Installation was undertaken between late January and early March 2025, with fabrication, delivery, and field installation coordinated through a just-in-time workflow. The significance of this performance is not simply the installation rate, but the ability of the system to provide immediate load-bearing capacity without a concrete curing period, thereby reducing program interfaces between foundation installation and equipment placement.

A project-specific embodied-carbon comparison further estimated approximately 281 kg CO₂e per helical pile compared with 518 kg CO₂e for an equivalent-diameter bored pile. The difference was driven not only by materials but also by concrete delivery, excavation, spoil handling, and transport requirements. These results are site-specific rather than universally transferable: the advantage was strongly influenced by the project’s distance from concrete supply and the absence of rock or major obstructions. The Limondale case therefore demonstrates that the principal benefit of helical piles arises from the interaction between suitable ground conditions, installation monitoring, rapid construction, and supply-chain constraints, rather than from an inherent superiority over bored foundations.

3.2. The Clean Peak Energy Solar Farm

A smaller-scale but illustrative example is the Clean Peak Energy solar farm in Wangaratta, Victoria, a 70-hectare facility officially commissioned in early 2025, where 49 helical piles were installed to find the array structures in difficult clay soil conditions with a short project lead time [98].

3.3. Comparative Reference Cases: Mixed- and Bored-Pile Foundation Projects

While Section 3.1 and Section 3.2 demonstrate large-scale applications of helical piles, major transmission projects often require multiple foundation types selected according to local ground conditions, structural demand, and constructability.

The 213 km, 500 kV Manitoba–Minnesota Transmission Project (MMTP), commissioned in 2020, comprised 502 transmission structures and used five foundation or anchor systems, including precast and cast-in-place concrete, micropiles, overburden-grouted anchors, and helical piles [99]. Foundation type was selected on a tower-by-tower basis. Helical and other alternative systems were adopted where seepage, unstable soils, or several meters of peat reduced the suitability of conventional concrete foundations. Manitoba Hydro reported that maintaining multiple foundation options improved construction flexibility and reduced delay risk [99]. By comparison, a large cast-in-place foundation at the Red River Floodway crossing, approximately 3 m in diameter and extending 12 m below grade, required about three months to construct. The case therefore illustrates that foundation selection is primarily condition-dependent rather than technology-dependent.

Project EnergyConnect provides a contrasting Australian example in which bored piles remained the principal foundation solution [100]. Their selection reflected the high structural loads and generally suitable ground conditions along much of the alignment. However, bored-pile construction required excavation, concrete supply, cranes, and pumping equipment, increasing site logistics and construction interfaces relative to rapidly installed foundation systems [100].

Together, these projects demonstrate that no single foundation system is optimal across an entire transmission corridor. Foundation selection should instead respond to local geotechnical conditions, structural loading, access, program constraints, and supply-chain requirements, with helical piles representing one option within a broader project-specific foundation strategy.

4. Comparative Metrics for Foundation Selection

Because transmission-foundation procurement typically commits to a single system at the design stage, this comparison combines independent project data for helical and bored piles with published productivity and cost relationships [70,71]. The values in Table 4, Table 5 and Table 6 should therefore be interpreted as representative screening ranges and refined for project-specific soil conditions, pile geometry, and supply-chain assumptions.

Table 4. Comparison of geotechnical and structural performance of helical and bored piles.

Geotechnical and Structural Performance	Helical Pile	Bored Pile
Load capacity	High capacity; verifiable through installation torque correlation or load testing [101].	High capacity (up to 9378 kN per pile); capacity is estimated and verified through post-installation testing [102].
Group efficiency/interaction	Lower group interaction; piles fail individually rather than as a block [89].	Higher group interaction; risk of block failure in closely spaced groups [89].
Suitability for challenging soils	Excellent; bypasses unstable layers to anchor in deep, stable strata or bedrock [51].	Can be problematic in reactive clay soils, where seasonal shrink-swell behavior can cause differential ground movement and foundation distress (a condition affecting roughly 20% of the Australian landmass) [103].
Quality control (QC)	Real-time capacity verification via torque correlation for every pile installed [73].	Capacity is estimated based on soil bore data; post-installation testing is required for verification [104].

Table 5. Comparison of installation and cost benefits of helical and bored piles.

Installation and Cost Benefits	Helical Pile	Bored Pile
Installation time/productivity	Very rapid; approximately 40–50 piles/day on large projects [96].	Slow; multi-day process per footing, with on-site drilling and concrete work [71].
Crew size	Small; 1–2 person crew per rig [50].	Large; requires specialized drilling, crane, and concrete teams [71].
Site disturbance	Minimal; no excavation, no spoil, and no vibration [65].	Extensive; requires excavation and management of soil spoil [104].
Cure time	Zero; immediate load-bearing capacity allows for instant construction [73].	Significant; concrete requires up to 4 weeks to reach full strength [105].
Environmental footprint	Lower embodied carbon (steel is recyclable); reduced water usage; minimal impact on soil and landscape [66].	High embodied carbon (concrete production is a major CO2 source); requires large amounts of water for curing; disrupts the natural landscape [66].

Table 6. Comparison of risk profile differences between helical and bored piles.

Risk Profile Difference	Helical Pile	Bored Pile
Latent conditions	Lower residual in-ground uncertainty after installation. Each pile generates installation torque and depth records, so part of the subsurface uncertainty is converted into measurable field data during construction. However, risk is not eliminated: torque–capacity correlation can still be mis-estimated if spatial variability is not properly accounted for [106].	Higher residual latent-condition exposure. Capacity and integrity remain more dependent on sampled geotechnical investigation and post-installation inspection. Published bored-pile defect literature shows that only a limited proportion of piles may be inspected in practice, and defects can lead to remedial work, disputes, delay, and added cost [107].
Weather delays	Lower weather sensitivity at the workface. Helical piles avoid wet-concrete curing and shift more activity into prefabrication and mechanical installation, reducing dependence on weather-sensitive site operations. Off-site construction literature also notes lower weather dependence on site when work is transferred to fabrication shops [108].	Higher weather sensitivity. Concrete-task productivity is materially affected by precipitation, wind, and temperature, and internationally documented evidence spanning both cold and hot climate conditions shows that adverse curing environments, whether near-freezing or extreme heat, can reduce concrete stiffness, strength, and durability [109,110]. This creates a more weather-exposed construction sequence for bored foundations, regardless of the specific climatic setting encountered along a transmission line alignment.
Supply chain	Moderate but more centralized supply-chain risk. Risk is concentrated in steel fabrication capacity, transport sequencing, and supplier coordination. When managed well, prefabrication can reduce duration and improve cost control, but off-site construction literature still identifies constraints related to factory capacity, transport, and knowledge integration [108].	Higher and more diffuse site supply-chain dependence. Delivery depends on drilling plant, reinforcement cages, concrete supply, and often casing/slurry systems and spoil handling. Pile productivity and cost are also sensitive to site planning and equipment maintainability [70,71].
Workforce	Lower on-site labor exposure. A greater share of work is shifted from the site to controlled fabrication, which can reduce on-site labor demand, shorten project duration, and reduce labor wastage, although skilled operators and QA review are still required [108].	Higher workforce exposure. Productivity depends on contractor experience, equipment maintainability, and coordination across multiple field crews and interfaces. This makes bored-pile execution more sensitive to labor availability and field-management quality [70,71].

Migunthanna et al. [66] provide a directly quantified comparison between a 3 m helical pile and an equivalent-length bored pier using Australian contractor data. For a representative 50-pile project, the helical system reduced global warming by 56% and energy consumption by 34%, with the largest savings arising during construction and end-of-life recovery. Although conducted at a smaller scale, the underlying drivers—lower material demand, fewer equipment requirements, and simpler end-of-life recovery—remain relevant to larger multi-pile transmission foundations.

Even Australia’s largest transmission project, the EnergyConnect interconnector in NSW, SA, and Victoria, has been actively evaluating helical piles as a superior alternative to its existing foundation approach. The decision to use bored piles on EnergyConnect was based on their ability to handle heavy structural loads and their suitability for good ground conditions, but they require significant on-site resources, including large-scale excavation, cranes, and concrete pumps, which can lead to longer project timelines and higher costs [100].

Table 4 provides a data-driven comparison of helical piles versus bored piles, summarizing geotechnical and structural performance, and Table 5 shows a comparison of the installation and cost benefits of helical and bored piles.

In addition to geotechnical performance and installation cost, foundation selection should also be evaluated in terms of delivery risk exposure. Table 6 compares the principal project-risk pathways associated with helical piles and bored piles. The classifications are comparative interpretations of the published literature rather than absolute rules, and actual exposure remains dependent on investigation quality, contractor capability, and the project procurement model.

The comparison in Table 6 indicates that the principal advantage of helical piles is not only faster installation, but a reduction in hidden-condition and interface risk during delivery. Helical piles tend to reduce the project exposure associated with unobserved in-ground defects, weather-sensitive concrete operations, and multi-interface site logistics. By contrast, bored piles remain a technically capable solution, but their risk profile is generally more dependent on field execution quality, inspection sufficiency, and weather-resilient site management.

Applicability Limits and Evidence Gaps

Helical pile groups should not be regarded as a universal alternative to bored or rock-socketed foundations. Their suitability is controlled by installability, structural demand, durability, and the level of confidence available for long-term performance. Installation torque increases with soil density, confinement, and pile geometry, while installation itself can substantially alter the surrounding soil; experimental studies in very dense and saturated sands demonstrate that helix geometry and advancement conditions strongly influence both installation torque and subsequent capacity [79,111]. Consequently, competent rock, cemented strata, cobbles, or other significant obstructions may cause premature refusal or require pre-drilling, whereas bored or socketed foundations can provide a more predictable solution where penetration to a prescribed founding level is essential. This limitation is particularly important because torque is simultaneously an installation constraint and an empirical indicator of axial performance. Because final installation torque governs both achievable depth and equipment selection, data-driven methods are emerging to predict torque at the design stage [112].

Structural demand provides a second boundary. Helical piles are particularly effective where uplift governs, as commonly occurs in transmission structures subjected to overturning, but lateral resistance is strongly dependent on shaft diameter and flexural stiffness [113]. Large axial loads or demanding lateral and moment conditions may therefore require multiple helical piles, larger shafts, or hybrid foundation configurations, reducing their economic advantage relative to a large-diameter bored pile. Existing full-scale group studies also show that pile–cap–soil interaction can materially influence system response, reinforcing the need to assess the group rather than extrapolate directly from isolated-pile capacity.

Cyclic behavior remains an important research limitation. Recent field testing in sand showed a stable response when cyclic tensile amplitudes were below approximately 13% of static tensile capacity, whereas amplitudes above approximately 22% produced progressive displacement accumulation [114]. These thresholds are site-specific and should not be treated as universal design limits. Similarly, field testing of a four-helix pile subjected to 50 tensile cycles between approximately 13% and 50% of its reference uplift capacity found no reduction in shaft resistance and an improvement in post-cyclic stiffness; however, the authors emphasized the limited field evidence available for multi-helix piles [115]. Thus, extrapolation to cohesive soils, high cycle counts, and multi-decade transmission-service loading remains premature.

Long-term serviceability and durability are additional evidence gaps. Previous reviews have specifically identified settlement as an area requiring further investigation [116], while published full-scale helical-pile group research remains considerably more limited than the literature on conventional pile systems. For steel helical piles, durability should also be treated as site-specific: field evidence shows that corrosion rates vary substantially with exposure conditions, including groundwater fluctuation and oxygen availability [117]. Accordingly, aggressive soils may require increased sacrificial thickness, galvanizing, or other protection measures, which should be included in whole-life comparisons.

Overall, foundation selection should therefore consider ground penetrability, axial and lateral demand, cyclic loading, durability, settlement, construction logistics, and whole-life cost together, rather than treating either system as inherently preferable. The principal research priorities are long-term monitoring of full-scale pile groups, cyclic testing under representative transmission load spectra and soil types, and improved links between installation measurements and group-level serviceability.

5. Environmental Aspects

Helical piles offer several key advantages over traditional concrete foundations, helping to reduce the overall environmental footprint and align with modern sustainability goals.

5.1. Ground Disturbance

Because installation is a displacement rather than excavation process, helical piles avoid the soil removal, exposed spoil, and open trenching associated with bored or driven foundations, leaving the surrounding soil profile largely intact [65]. This low-impact approach is particularly beneficial for projects that traverse environmentally sensitive areas.

5.2. Embodied Carbon and Recyclability

By eliminating or significantly reducing the need for large concrete footings, helical piles offer a lower-carbon alternative for foundations [66]. The values in Figure 8 were calculated by the authors as an indicative cradle-to-site comparison for a 50-pile project, with emission factors taken from the ICE v3 [118] and EPiC [119] embodied-carbon databases. The factors used were 2.5 kg CO₂e/kg for steel, 0.4 kg CO₂e/kg for galvanizing, 320 kg CO₂e/m³ for concrete, 2.0 kg CO₂e/kg for reinforcement, 2.7 kg CO₂e/L for diesel, and 0.11 kg CO₂e/t·km for road freight, with a 30 km one-way transport distance. Figure 8 compares the embodied carbon of one helical pile and one bored cast-in-place pile, broken down by component. The helical pile, with a length of 6 m and a diameter of 300 mm, emits about 331 kg CO₂e, of which steel (83%) and galvanizing (13%) account for almost all. The bored pile, with a length of 6 m, a diameter of 450 mm, and reinforcement of 90 kg/m³, emits about 539 kg CO₂e, mainly from concrete (57%) and reinforcement (32%). Rig fuel and spoil handling, spoil haulage, and concrete delivery together account for a further 63 kg CO₂e, about 12% of the bored pile’s total, whereas the helical pile’s installation fuel and transport produce only about 11 kg CO₂e. Overall, the helical pile emits about 208 kg CO₂e less per pile, a reduction of about 39%. For the 50-pile project, this corresponds to 16.6 t CO₂e against 27.0 t CO₂e, a saving of about 10.4 t CO₂e. The advantage arises mainly from replacing concrete and reinforcement (477 kg CO₂e per bored pile) with steel and galvanizing (320 kg CO₂e per helical pile), a material-stage reduction of about 33%, and from the absence of spoil, which lowers site-operation emissions by about 83%. These results should be interpreted with caution. The comparison assumes that both pile types provide equivalent capacity for the same application, that the helical piles are ungrouted, and that the boundary ends at the site gate, so end-of-life effects such as the potential removal and reuse of helical piles are not captured. The values are therefore only indicative, are not a verified life-cycle assessment or environmental product declaration, and depend on the assumed pile geometry and emission factors.

Figure 8. Indicative embodied carbon per pile (kg CO_2e, cradle-to-site) for a helical pile and a bored cast-in-place pile, by component (calculated by the authors using ICE v3/EPiC emission factors; not a verified LCA).

This is further enhanced by the fact that the piles are made from steel, which is a highly durable and nearly infinitely recyclable material [120]. At the end of a structure’s life, helical piles can be extracted more readily than drilled shafts or driven piles [121] and either reused or recycled, supporting a circular economy [120].

The environmental benefits of helical piles are not merely a sustainability add-on; they are a core business case consideration. AEMO’s 2024 ISP includes a specific appendix on social license [122], acknowledging the importance of community acceptance for project success. Community opposition and environmental concerns can cause significant project delays and cost overruns. By adopting a foundation system that minimizes ground disturbance, noise, and carbon emissions, transmission providers can build trust and acceptance, thereby de-risking the project timeline and budget [123].

6. Life-Cycle Cost Analysis

A technically robust comparison between helical piles and bored piles should not end at initial construction cost; it should instead be framed as a whole-of-life economic assessment. Recent transmission-line life-cycle cost studies define total life-cycle cost as the combined present value of initial investment, operation and maintenance, periodic maintenance, failure/remedial costs, and end-of-life disposal, with any salvage value credited against disposal cost [124]. This broader framing is especially relevant for tower foundations because communication-tower life-cycle cost research shows that long-term project economics are affected not only by material quantities, but also by policy standards, management capability, environmental constraints, procurement errors, design deviations, construction delays, and operational failure [125]. Accordingly, the economic comparison between helical and bored foundations should be expressed as a discounted cash-flow problem rather than a simple first-cost comparison.

Jin et al. [126] present a life-cycle cost model for engineering structures that decomposes total cost into five discrete stages, each discounted to present value and then summed. The planning and design cost (C_D) captures survey and design fees accrued over the design period; the production and construction cost (C_C) captures construction and ancillary costs accrued over the construction period; the inspection and maintenance cost (C_I) and the separate maintenance and reinforcement cost (C_M) each aggregate their respective interventions across the structure’s service life; and the disposal and recycling cost (C_R) captures demolition and treatment costs net of any recycling revenue at the end of service life. The total life-cycle economic cost is expressed as

C_LC = C_D + C_C + C_I + C_M + C_R

(2)

For bored piles, the relevant first-cost components (C_D and C_C) typically include drilling, reinforcement, concrete supply, spoil handling, curing-related preliminaries, and the plant fleet needed to support those operations [71]. In contrast, a recent Australian comparative life-cycle analysis of screw piles and bored piles reports that screw-pile installation is operationally simpler, and that bored-pile construction requires additional equipment such as concrete truck mixers, loaders, and tipper trucks, with further dewatering requirements arising under rainy conditions [66]. This is consistent with prior pile-construction productivity research showing that pile cost is strongly influenced by site planning, equipment maintainability, and subsurface uncertainty, rather than by material quantities alone [71]. For transmission projects in remote or access-constrained corridors, these indirect and logistics-related terms can therefore materially affect C_LC and should be considered.

The distinction between the two systems becomes even clearer when future cost streams are considered. Routine maintenance may be modest for both alternatives under normal inland exposure, but it should not be assumed to be zero. Life-cycle cost research on pile-supported infrastructure demonstrates that aging, corrosion, and damage accumulation can materially increase long-term cost. In one pile-supported wharf study [127], corrosion increased structural life-cycle cost by about 15% and total system life-cycle cost by about 8%. Although that study concerns a harsher marine environment than an inland transmission corridor, it confirms the methodological point that future inspection, maintenance, and failure-related costs (C_I and C_M) should be retained in the model. In practical terms, bored piles are more exposed to uncertainty associated with hidden defects and remedial intervention, whereas helical piles benefit from a more direct installation record through torque and depth logging; therefore, the remedial-cost terms can reasonably be expected to be lower for helical piles. This inference is a project-risk judgment rather than a universal rule.

A recent Australian cradle-to-grave comparison between screw piles and bored piles found that screw piles have a simpler deconstruction process, generate much less waste, and, for the average case studied, exhibit 85% lower end-of-life global warming potential (GWP) and 84% lower end-of-life energy consumption than bored piles. The same study notes that screw piles can be fully recycled, whereas bored-pile demolition is more waste-intensive [66]. While those results are environmental rather than monetary, they support the economic direction of the model (C_R). Screw piles generally carry a lower decommissioning burden, and the recovery of steel is also feasible. On this basis, the decision criterion becomes straightforward: the preferred alternative is the one with the lower discounted whole-of-life cost (C_LC), not necessarily the lower first cost. For remote transmission projects, helical piles are likely to show a lower C_LC when savings in logistics, preliminaries, delay exposure, and end-of-life burden are captured explicitly; however, the magnitude of that advantage remains project-specific and should be tested using the local soil profile, pile geometry, corrosion design, and supply-chain assumptions.

7. Recommendations for Codes and Practice

The design and installation of helical piles in Australia are governed by AS 2159, which provides a robust, performance-based framework rather than prescriptive, technology-specific guidance [74]. While this flexibility supports engineering innovation, the absence of standardized parameters such as soil-specific capacity-to-torque (Kt) factors and helix geometries can lead to significant design variability. Some examples are available internationally, such as the International Building Code (IBC) in the United States. The IBC provides clear, pre-established guidelines and default capacity-to-torque (Kt) factors for specific pile geometries [128]. Beyond the comparison between AS 2159 and US practice (the IBC and ICC-ES AC358), international practice provides useful context. The first-generation Eurocode 7 (EN 1997-1:2004) adopts a general performance-based framework for pile foundations, permitting verification through load testing, validated analytical or empirical methods, or comparable foundation performance, rather than prescribing helix-specific torque-to-capacity factors. These provisions are being superseded by the second-generation Eurocode 7, with piled foundations addressed principally in EN 1997-3:2025. Canada similarly combines general foundation-design requirements with product-specific technical evaluations for helical pile systems. New Zealand provides dedicated guidance through Practice Note 28, Screw Piles: Guidelines for Design, Construction and Installation (2015) [129], although its torque–capacity relationships require site-specific validation rather than prescribed Kt values. A broader review of screw-pile design methods is provided by Mohajerani et al. [116]. Collectively, these approaches show that the performance-based treatment of helical piles is not unique to Australia; however, the United States provides more explicit, pre-established torque-correlation criteria through ICC-ES AC358.

8. Conclusions

This review does not establish a general superiority of helical pile groups over bored piles, but rather identifies conditions in which they offer clear technical and construction advantages. In suitable soils, particularly where uplift or moment loading is important and concrete supply or program constraints are significant, helical piles can provide competitive capacity with faster installation, lower embodied carbon, and installation-torque-based quality control. Bored or rock-socketed piles remain preferable in hard, obstructed, or highly aggressive ground and where very high axial or lateral stiffness is required.

Foundation selection should therefore be based on an integrated assessment of ground conditions, structural demand, durability, constructability, cost, and carbon rather than on foundation type alone. Future research should strengthen correlations between installation torque and long-term group performance, including cyclic loading, settlement, and corrosion. Industry adoption would also benefit from standardized monitoring protocols, real-time installation data, and decision-support tools integrating geotechnical, structural, economic, and environmental criteria.