Load Design Standards for Ground Screw Foundations Explained

Purpose of Structural Load Standards

Structural load design standards define the methodology by which a foundation engineer translates the physical forces acting on a structure — gravity, wind, snow, seismic, and thermal — into a specific pile section, embedment depth, and installation specification that will safely resist those forces throughout the project design life. Without a defined load standard, the phrase “structurally adequate foundation” has no quantitative meaning — one engineer might apply a safety factor of 1.5 while another applies 3.0, producing structurally identical piles with identical soil conditions but wildly different design utilisation ratios and very different probabilities of failure. Load standards eliminate this ambiguity by specifying: the characteristic load values that must be derived from site and structural data; the load combinations that must be checked (dead load plus wind, dead load plus snow plus wind, and so on); the partial safety factors or overall factors of safety that must be applied to produce design loads from characteristic loads; the capacity model that converts soil investigation data and pile geometry into a calculable resistance; and the acceptance criterion that the calculated or tested resistance must satisfy relative to the factored design load. The Premium Technical helical pile design guide confirms that limits are evaluated at ultimate load using a factor of safety of 2.0 unless local codes require different criteria — illustrating how load standards translate the abstract requirement for structural safety into a specific numerical threshold that governs every pile specification decision. Load compliance is one component of the complete engineering framework for structural ground screw foundations — including material standards, galvanizing specifications, and corrosion protection requirements — described in our Ground Screw Standards Guide →

Scope of Application in Solar and Infrastructure Projects

Load design standards apply to ground screw foundations across the full range of solar and structural applications — from residential deck footings where a single pile supports 15–30 kN of gravity load, through agricultural solar ground mounts where wind uplift may govern at 20–50 kN per pile, to utility-scale single-axis tracker foundations where combined axial compression, wind uplift, lateral shear, and bending moment must all be simultaneously verified under multiple factored load combinations. For solar farm applications, the Helical Pile World solar foundation study confirms that helical piles can resist lateral loads and moments in both cohesive and cohesionless soils — with axial compressive and tensile (uplift) capacities predictable using the individual helix bearing method, and lateral resistance governed by the passive soil reaction on the pile shaft. The load standard applicable to a specific project is determined by the project jurisdiction (Eurocode 7 in the EU, IBC/ASCE 7 in North America, AS 2159 in Australia) and the type of structure supported (solar racking follows the structural building code for the jurisdiction, not a specialist solar code — making ASCE 7-22 the nationally adopted loading standard for all structural design including solar foundations in the United States). For international projects where both European and North American parties are involved, the project specification must explicitly nominate which standard governs each design check — because the two frameworks use different load factor values, different partial factor structures, and different capacity model approaches that produce different design pile specifications for identical site conditions when applied independently.

Who Requires Load Verification in EPC Contracts

Load verification is required at multiple levels of the project hierarchy for solar farm ground screw foundations. At the statutory level, building-permitted foundation systems in IBC jurisdictions must comply with IBC Section 1810 deep foundation requirements, which mandate that helical pile capacity be demonstrated either through a design calculation using the ICC-ES evaluation report’s torque correlation method (Qu = Kt × T) or through on-site static load testing per ASTM D1143 (compression) or ASTM D3689 (tension). At the engineering specification level, the structural engineer of record is required by professional liability standards to verify that every pile in the installation meets the design allowable load — which, in practice, means specifying the minimum installation torque criterion that every pile must achieve during installation, and requiring load testing on a defined percentage of piles to confirm the Kt factor used in the torque-to-capacity correlation. At the EPC contract level, solar farm EPC agreements typically specify that the foundation supplier must provide a signed engineer’s calculations package demonstrating code compliance for the complete load case set, installation records confirming that every pile met its minimum torque criterion, and a pre-production load test report confirming the site-specific Kt factor. At the project finance level, independent engineers reviewing utility solar technical due diligence require the complete load verification package — calculations, test reports, and installation torque records — as a standard deliverable confirming that the foundation system’s design basis is adequate for the project’s bankable energy yield model and PPA term.

Axial Compression Load Requirements

Axial compressive load capacity is the ground screw’s resistance to vertical downward force — the combined weight of the supported structure, equipment, snow accumulation, and any downward wind component under specific load combinations. The compression capacity of a helical ground screw is developed through two mechanisms: end bearing of the helical plate against the undisturbed soil below the plate (governed by the soil’s undrained shear strength in clay or internal friction angle in sand, acting on the projected area of the helix plate); and skin friction along the embedded shaft above the helix plate (governed by the soil-steel interface friction coefficient and the effective overburden stress at each depth increment). The Chance Technical Design Manual confirms that the shaft transfers the axial load to the helical plates and on to the soil bearing stratum — with the shaft needing to be strong enough to resist the combined torque and axial compression without yielding, and the soil providing the ultimate resistance against which the helix plate bears. The individual plate bearing method — summing the bearing capacity contribution of each helix plate independently — is the standard capacity calculation approach in North America (per ICC-ES AC358) and is confirmed by Helical Pile World solar plant field testing, which showed that the individual helix bearing method accurately predicts compressive capacity in both cohesive and cohesionless soils. For standard solar racking applications, axial compressive demand per pile ranges from 10–80 kN depending on the racking system weight, panel configuration, and snow load zone — within the capacity range of standard commercial ground screw products at typical embedment depths.

Uplift Resistance Standards

Uplift resistance — the pile’s capacity to resist vertical tensile forces pulling the pile out of the ground — is frequently the governing load case for solar farm foundations, because wind suction on the panel surface generates tensile uplift forces that can exceed the compressive demand from gravity loads in high-wind zones. The uplift resistance of a helical ground screw is primarily provided by the bearing capacity of the helical plate acting upward against the soil above the plate (the inverse of the compressive mechanism), with skin friction along the shaft providing a secondary contribution. This is a structural advantage of helical pile systems over smooth-shaft driven piles and concrete pads: the helical bearing plate provides a discrete, well-defined tensile resistance mechanism that is directly and simultaneously verified by the installation torque monitoring (the torque-to-capacity relationship Qu = Kt × T applies equally in compression and tension). The US Helical Piers load testing reference confirms that uplift testing per ASTM D3689 ensures piles won’t fail when subjected to wind, seismic, or overturning forces — and that ASTM D3689 is the applicable standard for static tensile (uplift) load testing of all helical pile types. For solar applications, the Sunmodo ground screw specification document confirms that ground screws and helical piers must be tested to 1.5 times the design uplift reaction — confirming that the load test load level is 1.5× the allowable design load, consistent with the required factor of safety of 1.5 on the tested capacity relative to the allowable working load under ASD.

Lateral Load and Bending Capacity

Lateral load resistance — the pile’s capacity to resist horizontal forces from wind pressure on the structure, seismic acceleration, or eccentric vertical loads — is governed by passive soil resistance acting on the embedded shaft as it deflects under lateral load, producing a soil reaction profile that the pile shaft must carry in bending. The Nature journal helical pile lateral research (2025) confirms that the helix plate contributes additional soil resistance to lateral load beyond that of an equivalent plain shaft — with the helix-to-pile diameter ratio (dH/dP) and the helix depth-to-pile embedment ratio (zH/zP) governing the magnitude of this helix contribution, and confirming that the helical contribution to lateral resistance diminishes beyond a depth ratio of 0.6, where the pile behaves similarly to a conventional plain shaft. Lateral pile analysis is conducted using the p-y spring model — the foundation of the LPILE and DeepFND software platforms — in which the soil is represented by a series of nonlinear springs at each depth increment, with spring stiffness (the subgrade modulus) derived from soil investigation data. The Deep Excavation lateral analysis example confirms that structural codes and safety factors must be defined for both bearing capacity and shaft structural checks — lateral pile design requires both a geotechnical capacity check (passive soil resistance sufficient to limit head deflection within the serviceability limit) and a structural capacity check (pile section modulus sufficient to carry the maximum bending moment without exceeding yield stress). For solar tracker applications in extreme wind zones, ASTM D3966 governs the lateral load test procedure — with the Sunmodo specification confirming that piles must be tested to 2.0× the design lateral reaction under ASD.

Partial Safety Factors and Load Combinations

Load combinations and safety factors are the bridge between the characteristic loads derived from site and structural analysis and the design loads that pile capacity must exceed — they account for the statistical uncertainty in load prediction, the variability in material strength, and the consequence of structural failure in a single numerical framework. The following table summarises the governing load types, applicable standards, typical safety factors, and structural failure modes for ground screw foundation design:

The Premium Technical helical pile design guide confirms that combined axial and lateral loads are evaluated at ultimate load using a factor of safety of 2.0 unless local codes require different criteria — confirming that the interaction between load types must be checked simultaneously, not independently, under the governing combined load case.

Static Load Testing (On-Site Pull-Out Tests)

Static load testing is the definitive method for confirming the in-place capacity of installed ground screws — providing a direct empirical measurement of pile resistance under controlled loading conditions in the actual project soil, at the actual installation depth, and with the actual installation torque and pile geometry of the production system. The US Helical Piers load testing analysis confirms that load testing for helical piles is governed by ASTM D1143/D1143M (static axial compressive load), ASTM D3689 (static axial tensile load), ASTM D3966 (lateral load), and ICC-ES AC358 (acceptance criteria for helical foundation systems). The ASTM D1143 Quick Test procedure — the most commonly specified test method for pre-production helical pile load tests on solar projects — applies load increments to the pile head at defined time intervals (typically 5-minute increments at 5–10% of the estimated ultimate load per step) up to the test maximum load (typically 200% of the design allowable load for a standard load test), measuring pile head deflection at each step and plotting the load-deflection curve. The Helical Pile World solar plant study confirms that axial compression and tensile load tests were carried out using the Quick Test procedure per ASTM D1143-07 and D3689-07 — with the primary objective being to determine the ultimate bearing capacity using the Davisson offset limit or the Butler-Hoy method applied to the load-deflection curve, and to derive the site-specific Kt factor that confirms the torque-to-capacity correlation used to accept production piles by torque monitoring alone.

Laboratory Load Testing

Laboratory load testing for ground screws — performed in controlled soil tank or calibration chamber conditions — provides the research-grade data that underpins ICC-ES evaluation reports and manufacturer design manuals, supplementing on-site field testing with parametric studies that vary pile geometry, steel grade, helix configuration, and soil properties independently. The VersaPile helical pile load testing guide confirms that load test standards such as ASTM D1143 and D3689 inform how a load test should be designed, performed, and interpreted — with the laboratory environment allowing precise control of soil density, moisture content, and pile installation torque in a way that is not achievable in field conditions. Laboratory test data is used to establish: the Kt factor ranges for different soil types and installation conditions (the empirical constant that converts installation torque to ultimate capacity); the plate bearing area efficiency factors for multi-helix configurations where helices interact under load; the interface friction coefficient for the shaft skin friction model; and the service life of galvanizing in laboratory-controlled soil chemistry conditions for corrosion protection design. For project-specific laboratory testing — particularly on unusual soil types, large-helix configurations, or new pile sections not covered by existing ICC-ES evaluation reports — the RADIX testing methodology confirms that ground screws can be tested for compression, vertical uplift, and horizontal load-bearing capacities to engineers’ specifications and to EN 1997-1 (Eurocode 7), deploying screws of various diameters and lengths specific to project requirements.

Finite Element Analysis and Engineering Simulation

Finite element analysis (FEA) and numerical geotechnical simulation provide the engineering team with a tool for load capacity prediction, pile behaviour assessment, and parametric optimisation that extends beyond what is achievable through either simplified analytical models or physical load tests alone. For helical pile lateral load analysis, the modified p-y springs method — the foundation of the DeepFND and LPILE software tools — models the soil-pile interaction along the full embedded shaft length using discrete nonlinear spring elements, with each spring’s load-deflection behaviour derived from empirical p-y curves calibrated to measured field and laboratory test data for the specific soil type. The Deep Excavation example confirms that FEA for helical piles requires definition of structural codes and safety factors for the structural section check, in addition to the geotechnical spring parameters for the soil resistance check — making the analysis a fully coupled structural-geotechnical calculation rather than two separate independent checks. The Nature journal 2025 helical pile study used the modified p-y springs method with empirically adjusted geotechnical parameters from field measurements, and machine learning analysis to optimise the helix-to-pile diameter ratio for lateral load performance — confirming that FEA-based optimisation of pile geometry for site-specific conditions can produce meaningfully better lateral resistance than standard library configurations, particularly for piles in soft clay where helix contribution to lateral resistance is most significant.

Acceptance Criteria for Load Tests

The acceptance criterion applied to a ground screw static load test — the rule that determines whether the tested pile passes or fails at the test load level — must be defined in the test specification before testing begins, and documented in the test report with the measured load-deflection data. Three acceptance criteria are in common use for helical ground screw load tests in solar farm applications. Davisson offset limit: a pile-head displacement limit derived from the pile’s elastic compression plus a fixed displacement offset (typically 4 mm + B/120 where B is the pile diameter in mm) — the criterion used in ASCE/ASTM practice for compression piles as a serviceability-based acceptance rule. Butler-Hoy method: the load at which the load-deflection curve departs from a defined slope, interpreted as the onset of plastic displacement — a capacity-based criterion that identifies a meaningful change in pile behaviour rather than a fixed displacement limit. Torque-to-capacity correlation: where ICC-ES AC358 is the governing acceptance framework, the ultimate capacity from the load test is compared against the predicted capacity from the installation torque using Qu = Kt × T, and the site-specific Kt factor is determined from the test results — used to calibrate the production pile acceptance criterion (minimum installation torque to achieve the required design capacity). The Hubbell Chance load testing guide confirms that load tests are conducted per ASTM D1143 (compression) or ASTM D3689 (tension), and that a larger-than-default Kt factor may be desired when site conditions are known to produce higher-than-average torque-to-capacity ratios — making the pre-production load test a commercial tool for pile specification optimisation as well as a quality assurance requirement.

Influence of Steel Grade on Load Capacity

The structural load capacity of a ground screw shaft is directly determined by the mechanical properties of the steel from which it is fabricated — yield strength, tensile strength, and torsional shear strength — making the steel grade specification and its material certification a structural load compliance requirement, not merely a materials quality management issue. The Chance Technical Design Manual confirms that the shaft needs to be larger than the shaft material’s allowable stress, and strong enough to resist the torque required for installation — establishing the explicit link between the steel’s yield strength (which determines allowable stress) and the achievable installation torque (which governs the maximum achievable pile capacity via the Kt correlation). For S355J2 steel (355 MPa minimum yield, the standard grade for commercial solar ground screws), the torsional yield capacity of a 76 mm OD × 5 mm wall hollow shaft is approximately 12 kN·m — setting the maximum installation torque that can be applied before torsional yielding, and therefore the maximum achievable pile capacity under the Kt correlation. For S235JR steel (235 MPa minimum yield), the same section yields at approximately 8 kN·m — a 33% reduction in maximum achievable torque and therefore in the pile’s maximum achievable capacity at the same shaft dimensions. This steel grade effect on load capacity is the engineering reason why downgrading from S355 to S235 steel cannot be compensated by increasing shaft wall thickness without a complete structural recalculation — the two changes affect different structural parameters (diameter governs bending; wall thickness governs torsion and axial stress). Material strength classifications and their engineering implications are explained at Steel Grade Standards for Ground Screws →

Impact of Corrosion on Long-Term Structural Resistance

Corrosion reduces the structural load capacity of a ground screw through progressive section thickness loss — reducing the shaft’s cross-sectional area, section modulus, and moment of inertia over time in proportion to the corrosion rate and elapsed service time. For a 76 mm OD × 5.0 mm wall shaft with an aggressive zone corrosion rate of 0.07 mm per year (Zone 2 — grade interface zone in the Helical Pile World zoning model), the section loss after 25 years is 0.07 × 25 = 1.75 mm of radial thickness loss — reducing the effective wall thickness from 5.0 mm to 3.25 mm, a 35% cross-section area reduction. This 35% area reduction produces a 35% reduction in axial capacity, a 52% reduction in section modulus (since section modulus scales with the square of thickness for thin-walled sections), and a 51% reduction in torsional moment of inertia — meaning that the pile’s bending capacity in the worst-case corrosion zone is less than half its as-new design value after 25 years if the zinc coating is completely depleted before that time. For this reason, the load design calculation at ultimate state must be performed at both the as-installed section geometry (governing the initial installation safety factor check) and the corroded section geometry at end of design life (governing the structural adequacy check for the full design period). Environmental corrosion categories and their impact on zinc coating service life and steel section loss rates are discussed at Corrosion Classes for Ground Screws →

Interaction Between Soil Conditions and Load Performance

Soil conditions govern the geotechnical component of ground screw capacity — the resistance that the soil provides to the applied structural loads through helix plate bearing, shaft friction, and passive lateral resistance — and therefore define the pile length, helix configuration, and installation torque required to achieve the design capacity for any given structural demand. The US Helical Piers load testing analysis confirms that key factors affecting load performance include soil conditions (weak, loose, or layered soils can reduce pile performance compared to dense or uniform soils), pile design (shaft diameter, helix size, and number of helices all affect load capacity), and installation torque (higher installation torque generally correlates with higher load capacity). The soil-pile interaction model requires characterisation of soil type (cohesive clay, cohesionless sand, or mixed profile), strength parameters (undrained shear strength Su for clay; friction angle φ for sand), and variability across the project footprint for the pre-production design phase, and confirmation of the achieved installation torque at every pile location for the production quality assurance phase. When soil conditions are softer than assumed in the design (producing lower-than-predicted installation torque at the design depth), the production pile acceptance criterion based on a minimum torque threshold will automatically identify under-performing piles before load transfer to the structure — which is the practical operational advantage of torque monitoring as a real-time capacity verification tool over any post-hoc load testing programme for production piles.

Eurocode vs ASCE/ASTM Load Design Philosophy

Eurocode and the US ASCE/ASTM/IBC framework represent two distinct philosophies for structural load design — both aimed at ensuring adequate structural safety, but through different mathematical frameworks that produce different numerical outputs from identical input data. The Eurocode framework (EN 1990 “Basis of structural design” governing the overall framework; EN 1997-1 governing geotechnical design) uses the partial factor method: characteristic loads are multiplied by load partial factors (γF — typically 1.35 for permanent loads, 1.5 for variable wind/snow) to produce design loads, and characteristic resistances are divided by resistance partial factors (γR — typically 1.3–1.5 for pile capacity, depending on the number of load tests and the design approach) to produce design resistances. Structural safety is confirmed when the design resistance exceeds the design load. The US IBC/ASCE framework uses both Load and Resistance Factor Design (LRFD) — applying load factors to characteristic loads and resistance factors to characteristic capacities, producing a factored demand vs factored resistance comparison — and the traditional Allowable Stress Design (ASD) — applying a single overall factor of safety (typically 2.0 with load test confirmation, 3.0 without) to the characteristic capacity to produce an allowable working load. The fundamental difference is in where the safety margin is applied: Eurocode separates the uncertainty in loads from the uncertainty in resistance through independent partial factors, producing a theoretically more rational treatment of the different uncertainty sources; ASD combines all uncertainty into a single factor of safety that is easier to apply but less calibrated to the relative magnitudes of load and resistance uncertainty for each specific application.

Ultimate Limit State vs Allowable Stress Design

The choice between Ultimate Limit State (ULS) design (the Eurocode LRFD approach) and Allowable Stress Design (ASD, the traditional US approach) has direct practical implications for ground screw pile specification — particularly in the interpretation of load test results and in the calculation of design capacity from torque monitoring records. Under ASD, the allowable pile load is the ultimate capacity (from load test or calculation) divided by the factor of safety: Q_allowable = Q_ultimate / FS. For a pile with a measured ultimate compression capacity of 180 kN and FS = 2.0, the allowable working load is 90 kN. Under ULS (LRFD), the design pile resistance is Rd = Qk / γR where Qk is the characteristic capacity from test results (typically the 5th percentile of multiple test results, or a mean with a correction factor for limited test data). For the same pile with Qk = 160 kN (characteristic from 3 load tests) and γR = 1.35 (Eurocode DA1 Combination 2 for compressive resistance with load tests), Rd = 160/1.35 = 119 kN. These two approaches give different allowable loads (90 kN vs 119 kN) from the same test data — confirming that the applicable design code is not interchangeable, and that a pile specified under ASD with FS = 2.0 is not automatically equivalent to a pile verified under Eurocode ULS with γR = 1.35. For international utility solar projects financed in Europe but constructed in North America, the project specification must confirm which framework governs the pile capacity calculation — and if both frameworks must be satisfied (e.g., for cross-border portfolio compliance), the more conservative result of the two independent checks governs the final pile specification.

Regional Compliance Variations

Beyond the EU/North America divide, several regional markets maintain specific code requirements that modify the standard Eurocode or ASCE load design framework for ground screw applications. In Australia, AS 2159:2009 governs pile design using a risk-based geotechnical strength reduction factor (φg) ranging from 0.45 (highest risk — complex soil, no testing) to 0.90 (lowest risk — simple soil, extensive testing) — a design approach that explicitly rewards pre-production load testing with a reduced conservatism factor, producing more economical pile specifications on well-tested projects. In Canada, the National Building Code of Canada (NBCC) governs load derivation, and CSA A23.3 and CSA S16 govern structural design — with the geotechnical pile capacity design typically following Eurocode 7’s partial factor approach under the Canadian Geotechnical Society’s Canadian Foundation Engineering Manual. In the UK (post-Brexit), the retained Eurocodes with UK National Annexes apply to structural and geotechnical design — with the UK National Annex specifying UK-specific values for the nationally determined parameters (NDPs) in EN 1997-1, including the geotechnical resistance partial factors for different verification approaches. For utility solar projects in the Middle East and Southeast Asia — where no national building code specifically addresses helical pile foundation design — ICC-ES evaluation reports are increasingly used as the technical compliance pathway, supplemented by project-specific load testing requirements specified by the lender’s independent engineer.

Engineering Calculation Reports

The engineering calculation report is the primary document demonstrating that the ground screw foundation system is structurally adequate under all applicable load combinations — and it must be prepared, signed, and sealed by a licensed structural or geotechnical engineer of the applicable jurisdiction. A complete load design calculation report for a solar farm ground screw foundation programme includes: the site geotechnical data summary (soil profile, strength parameters by layer, groundwater level) derived from the site investigation; the structural load derivation from the solar racking system geometry and the applicable load standard (ASCE 7-22 or Eurocode 1), including wind pressure coefficients, snow load, dead load, and all relevant load combinations; the pile capacity calculation using the individual plate bearing method or the torque correlation method, demonstrating compliance with the required safety factor or partial factor for each load combination; the pile section structural capacity check under axial compression, tensile uplift, combined lateral and axial loading, and torsional installation torque; the minimum installation torque criterion derived from the Kt factor for the site soil conditions; and the deflection serviceability check confirming that pile head displacement under working load does not exceed the racking system’s structural tolerance. The calculation report is the engineering bridge between the soil investigation data and the production installation specification — without it, the installation torque criterion has no defensible engineering basis, and the project cannot demonstrate that the installed foundation system meets the code requirements.

Load Test Reports

A conforming load test report for ground screw foundations must document the complete test programme from pile installation through final data reduction in sufficient detail to allow an independent engineer to review the test methodology, verify the data reduction, and confirm the capacity interpretation. The minimum content of a conforming ASTM D1143 or D3689 load test report includes: the test pile installation record (pile type, dimensions, steel grade, installation torque-depth log, final installation torque, date and equipment identification); the test setup description (reaction frame geometry, hydraulic jack specification, tell-tale gauge or displacement transducer locations and calibration certificates); the test loading procedure (quick test or maintained load procedure, load increment schedule, hold times at each increment); the complete load-deflection data table (applied load in kN, measured displacement in mm at tell-tale and reference points, at each loading and unloading step); the load-deflection curve plots (to scale, with the capacity interpretation method and derived ultimate load identified); the Kt factor calculation (ultimate capacity from test ÷ average installation torque from log) for each test pile; and the pile acceptance recommendation — confirming the minimum production installation torque that ensures the design allowable load is achieved at each production pile location. The US Helical Piers analysis confirms that load testing confirms whether piles can safely support the design load, how much settlement or deflection occurs under load, and whether the pile meets local code requirements and safety factors — establishing load testing as a confirmation of the complete design basis, not merely of one performance parameter.

Third-Party Structural Certification

Third-party structural certification — independent review and sign-off of the engineering calculation package, load test programme, and installation records by a qualified engineer who is not the designer of record — provides the independent verification of structural compliance that lenders, insurers, and regulators require for major utility solar projects. The certification process typically involves: independent review of the design calculation report for code compliance, correct load derivation, and appropriate capacity model selection; independent review of the load test reports for test methodology compliance with the applicable ASTM standard, data quality, and capacity interpretation correctness; audit of the production installation torque records against the minimum torque criterion specified in the calculation report; and issuance of a structural compliance certificate confirming that the foundation system as designed and installed meets the requirements of the applicable code for the project’s design life, load case set, and site conditions. For ICC-ES evaluation report compliance, the evaluation report itself constitutes a form of third-party certification — confirming that the specific pile system design (geometry, steel grade, helix configuration, torque correlation) has been independently evaluated for compliance with the IBC. For Eurocode-governed projects, the equivalent is a Notified Body product certification or a project-specific Technical Approval (ETA — European Technical Assessment) issued by a designated Technical Assessment Body. Load verification works together with coating compliance, material certification, and corrosion protection documentation to form the complete engineering compliance package described in our Ground Screw Standards Guide →

Are Load Tests Mandatory for Solar Projects?

Load testing requirements for solar ground screw foundations depend on the project jurisdiction, the pile system’s ICC-ES or equivalent evaluation report status, and the lender’s independent engineer requirements. In IBC-governed jurisdictions, ICC-ES AC358 requires load testing on a percentage of installed piles — typically defined in the project-specific design documentation — with the minimum testing programme determined by the risk level of the project and the degree of confidence in the site-specific Kt factor. In Eurocode-governed jurisdictions, EN 1997-1 Design Approach 1 (Combination 2) requires the characteristic pile capacity to be determined from load test results rather than purely from soil parameter calculations, unless the design approach explicitly permits the calculation route with an increased model uncertainty factor — effectively making load testing the preferred, though not absolutely mandatory, verification method. The Hubbell Chance load testing guide confirms that there are many scenarios where a load test will be required — including when piles refuse on a dense layer before reaching the required torque, when a larger-than-default Kt factor is desired, when soil information is lacking or unknown, and when the project engineer requires one — confirming that mandatory load testing is governed by project-specific risk factors as much as by code requirements. For utility solar projects financed by international project lenders, load testing is effectively mandatory regardless of the statutory position — independent engineers require a pre-production load test programme as standard due diligence evidence that the Kt factor used in the torque acceptance criterion is appropriate for the specific project site.

When Is On-Site Testing Required?

On-site static load testing is required — by code, by engineering best practice, or by commercial risk management — in the following specific project scenarios. Variable or unknown soil conditions: where the site investigation reveals significant variability in soil strength or type across the project footprint, an on-site test programme confirms the site-specific Kt factor for each distinct soil zone, preventing the systematic under-specification of piles in softer zones. Refusal on dense layer: when production piles refuse (stop advancing) on a dense soil layer or partial obstruction before reaching the required installation torque, on-site compression load testing of the refused pile confirms whether the achieved embedment depth provides adequate compressive capacity — potentially allowing acceptance of the short pile if testing confirms adequate capacity, or triggering pile replacement if capacity is insufficient. Enhanced Kt factor needed: when the standard Kt correlation from the ICC-ES evaluation report produces a conservative (high) required torque that piles cannot consistently achieve in the actual site soil, an on-site test programme with back-calculated Kt can demonstrate that a lower torque is sufficient to confirm the required capacity, reducing installation failures and improving productivity. Lender or independent engineer requirement: for all utility solar projects above 1 MW financed by institutional lenders, the independent engineer will typically require a pre-production load test programme covering both compression and tension at a minimum of two locations representative of the range of soil conditions encountered on site, regardless of whether the code strictly mandates it.

How to Evaluate Supplier Load Capacity Claims?

Ground screw suppliers routinely publish allowable load tables in their product literature — tables that present maximum allowable compression, tension, and lateral loads for each product size across a range of soil conditions or installation torque levels. Evaluating the engineering credibility of these published claims requires reviewing the underlying evidence that supports them, not just accepting the table values at face value. The following checklist covers the minimum evidence required to evaluate a supplier’s load capacity claims for a structural application. (1) ICC-ES evaluation report or equivalent: the pile system should have a current ICC-ES evaluation report (for North American projects) or European Technical Assessment (for EU projects) that documents the code compliance basis for the capacity claims, including the range of soil conditions, pile dimensions, and installation torques within which the published capacities are valid. (2) Load test programme: the supplier should be able to provide ASTM D1143 and D3689 test reports from load tests on the specific pile section and helix configuration being specified, in soil conditions comparable to the project site. (3) Site-specific Kt factor range: the published allowable loads should be derived from a defined Kt factor range — confirm that the Kt value used to back-calculate the published allowable loads from the installation torque is appropriate for the project site’s soil type. (4) Safety factor confirmation: confirm whether the published values are allowable working loads (ultimate capacity ÷ FS 2.0) or ultimate capacities — the distinction is a factor of 2.0 in the design allowable load. Load standards are one part of the broader compliance framework governing structural ground screw foundation adequacy, available at Ground Screw Standards Guide →

Checklist for Structural Load Compliance

The following checklist summarises the minimum structural load compliance actions for solar farm ground screw foundation programmes:

• ✅ Nominate the governing load standard — confirm whether ASCE 7-22 (North America), Eurocode 1 + 7 (EU), or AS 2159 (Australia) governs the project, and document this in the project specification before any design work begins
• ✅ Derive characteristic design loads — calculate wind uplift, wind lateral, dead load, snow load, and seismic load (where applicable) from the governing load standard, using the correct exposure category, importance factor, and load combination factors for the specific site and structure type
• ✅ Prepare geotechnical calculation report — calculate pile capacity using the individual plate bearing method or torque correlation method, demonstrate the required safety factor or partial factor is satisfied for every applicable load combination, and derive the minimum installation torque criterion for production piles
• ✅ Conduct pre-production load testing — minimum 2 compression and 2 tension static load tests per ASTM D1143 and D3689 (or EN 1997-1 equivalent), at representative soil condition locations, before production installation begins
• ✅ Establish and enforce the installation torque acceptance criterion — document the minimum torque threshold derived from the load tests and Kt factor, and confirm in installation records that every production pile meets or exceeds this criterion
• ✅ Perform section structural checks — verify shaft section capacity (axial, bending, torsional) under the governing combined load case at both as-new geometry and end-of-design-life corroded geometry
• ✅ Archive all documentation — retain design calculation report, load test reports, installation torque records, and third-party certification for the full design life of the project

Best Practices for Utility-Scale Solar Foundations

Utility-scale solar farm ground screw foundation programmes — with thousands of pile locations, multi-hundred-thousand-dollar foundation budgets, and 25-year bankable design lives — require load design best practices that go beyond the minimum code requirements to manage the commercial and structural risks that scale creates. The single most impactful best practice is the pre-production load testing programme: investing $15,000–40,000 in a six-pile test programme (compression and tension at three representative soil condition locations across the project footprint) before mobilising the production installation crew confirms the site-specific Kt factor, eliminates the conservatism in the ICC-ES default Kt ranges, and frequently enables a shorter, smaller-diameter pile to be specified at lower unit cost — with a payback period of a few hundred production piles on a large project. The second most impactful best practice is continuous torque monitoring with real-time data logging for every production pile: modern hydraulic drive heads record torque vs depth continuously as a digitally archived record, enabling post-installation analysis to identify anomalous locations where the torque profile suggests a soil condition departure from the design assumption — flagging piles for supplementary investigation or load testing before the racking system is installed over them. The third practice is zone-differentiated pile specification: using the pre-production test data to identify soil condition zones across the project footprint and specifying different pile lengths, helix configurations, or minimum torque thresholds for each zone — rather than applying a single conservative specification to the entire site — typically reduces average pile cost by 8–15% while maintaining or improving the structural reliability of the installed foundation system.

Integrating Load, Material, and Corrosion Standards

Structural adequacy of a ground screw foundation is not confirmed by satisfying the load design standard alone — it requires simultaneous compliance with three coupled engineering frameworks that together define whether the pile delivers its design load capacity over its complete design life. The load design standard confirms that the pile’s structural section and geotechnical embedment are adequate to resist the design loads at the time of installation, under the as-new pile geometry. The material standard (EN 10025 or ASTM A500 steel grade certification) confirms that the steel section’s mechanical properties match the values assumed in the structural calculation — preventing the scenario where an under-grade steel section fails the torsional installation check at a lower torque than the design assumed possible. The corrosion protection standard (ISO 1461 galvanizing compliance, verified by batch test report) confirms that the zinc coating service life is adequate to protect the structural steel section throughout the design period — preventing the scenario where the reduced-section structural check at end of design life produces a failing result because the zinc was depleted prematurely and the assumed corrosion allowance was consumed faster than the design predicted. These three frameworks are coupled: the load design calculation produces a required section geometry; the steel grade standard confirms the material properties of that section; and the corrosion protection standard confirms that the section geometry is maintained for the required duration. A foundation specification that satisfies only one or two of these three frameworks is not a compliant design — all three must be confirmed simultaneously through the complete documentation chain. To review all structural, material, and coating standards together in a single engineering compliance reference, visit the full Ground Screw & Solar Foundation Standards Guide →

👉 Request an engineering load calculation review or pre-production load testing programme design for your project:
Contact the Solar Earth Screw Technical Team →