Ground Screw or Helical Pile Substitution: Recheck the Design

A ground screw or helical pile substitution is not a like-for-like purchase unless the project proves that the changed foundation still satisfies the same ground, structural, installation, durability and approval requirements. Similar names, shaft diameters or quoted capacities do not preserve the design basis. First classify the proposed change, identify the exact before-and-after systems, and decide which earlier evidence remains representative. Then reopen every affected interface before ordering, installation or production testing continues. This guide gives EPC, design, procurement and construction teams a controlled substitution route. It does not select a foundation, calculate capacity, set installation torque, approve a product or replace the project’s geotechnical and structural authorities.

Classify the Change Before Comparing Price or Programme

Begin with the reason for the proposal. A supplier may use different terminology for the same identified product; procurement may propose a different source; a designer may alter shaft, thread or helix geometry; or site conditions may force a different installation concept. These cases do not carry the same technical burden.

Use a foundation substitution classification before discussing savings or delivery. The classification is provisional until controlled drawings and evidence confirm it.

If the team is still making the initial selection, use the broader ground screw vs helical pile comparison. This article starts later: a baseline, bid, submittal, test program or released design already exists and someone proposes changing it.

Do not let a commercial label decide the classification. Terms vary between markets, and the same label can cover different shafts, threads or helices, couplers and heads. The object of review is the installed system described by evidence, not the noun on a quotation.

Freeze the Before-and-After System Identities

A substitution cannot be evaluated against an incomplete baseline. Create two configuration records: the last authorized foundation system and the exact proposed replacement. Do not compare a detailed candidate with a generic description of the original.

For each side, record manufacturer and location; product family and code; drawing revision; shaft section, thickness basis, length and segment arrangement; thread or helix geometry; tip, couplers, extensions and head; materials and protection; manufactured joints; installation equipment and tooling; permitted orientation; termination method; structural connection; and intended project zones.

Identity also includes evidence. Link calculations, geotechnical recommendations, evaluation and test reports, installation instructions, quality plans and approved deviations to the configuration they represent. An undated catalogue or screenshot cannot prove that an option belongs to a reviewed family.

The ICC-ES explanation of an Evaluation Service Report notes that a report identifies the evaluated product, code or acceptance criteria, installation and identification conditions. The current AC358 listing is an acceptance-criteria route for helical pile systems and devices under named code editions and stated scope. Neither source means that every screw-shaped foundation, variant or project application is covered. Read the actual current report and its conditions; the authority having jurisdiction and project documents retain their roles.

Give every configuration a revision status such as baseline, proposed, under review, conditionally released or rejected. Procurement language such as “equivalent approved” should never appear before the responsible route has closed the evidence.

Reopen the Ground–Foundation–Structure Interface

The substitution review must begin at the reactions and performance criteria, not at a vendor table. Preserve the current structural reaction set with load directions, combinations or envelopes, application points, sign conventions and serviceability requirements. Confirm whether changes elsewhere in the mounting system have altered them. Then give the project geotechnical and foundation designers the exact proposed geometry and installation process.

The 2026 ASCE manual Design and Construction of Solar PV Structures, MOP 162 covers geotechnical investigation, load testing and foundation design, including frost, scour, special soils and corrosion. Its public summary says the investigation should determine subsurface design properties and recommend for the proposed foundation system. Site observations may remain useful after a change; concept-specific recommendations, models and tests do not automatically transfer.

Reconcile these interfaces:

• Ground model: stratigraphy, variability, fill, groundwater, obstructions, refusal risk, frost, scour, special soil behavior, exposure and investigation coverage.
• Geotechnical response: compression, tension/uplift, lateral response, rotation, movement criteria, group or spacing effects where relevant, cyclic or other project-defined conditions, and installation effects.
• Foundation structural response: shaft and helix/thread demands, couplers, head detail, unsupported length, durability, installation stresses and damaged-condition rules.
• Supported structure: head geometry, fixity or stiffness assumptions, eccentricity, tolerances, adjustment, connection and construction sequence.
• Project zoning: which locations share a design basis, which require separate treatment and what observation would move a location into another zone.

Never infer capacity from a soil name alone. “Clay,” “sand” or “fill” does not define the design profile, variability, groundwater, installation response or required performance. Likewise, a capacity printed for another site does not become a project value because the product looks similar. The appointed professionals must select the method and establish project-specific results.

Reset Installation Controls and Stop Rules

Installation is part of the foundation system. Changing from one form to another may change tooling, rotational speed, crowd or downforce, alignment control, sequence, extension handling, spoil or ground disturbance, obstruction response, head finishing, access envelope and the meaning of logged variables. It can also change equipment loads on roads, platforms, buried services or adjacent work.

Issue a proposed installation method before mobilization. Identify the exact equipment and tooling, competence, pre-start and utility controls, temporary stability, sequence, logged variables, instruments, termination logic, stop triggers, nonconformance route and location records. The project team must define numerical settings and limits; do not copy them from a different product, machine or soil zone.

Installation torque can be useful when the project has a validated relationship for the exact system, equipment, procedure and ground conditions. It is not a universal substitute for design or load testing. A changed shaft, helix/thread arrangement, coupler, tool, data method or ground zone can change what a torque reading represents. Treat any proposed correlation as evidence with a defined population and limitations, not as a transferable constant.

Set stop rules before production. Triggers include unidentified product, unapproved tooling, unexpected obstruction or refusal, alignment outside the released route, damage, incomplete data, instrument problems, installation variables outside the approved envelope, failed tests, or any break between reviewed configuration and installed item. A stop is a controlled state, not a field verdict on capacity.

Decide Which Existing Evidence Can Carry Over

Do not ask whether “the old report is still valid” as one yes/no question. Split the evidence by what it proves and the population it represents. Use an Evidence Carry-Over Matrix to reach one of four outcomes: retain, verify, replace or not applicable.

A load test represents the tested element, installation, ground condition, setup, direction, procedure and interpretation. It may answer the original question without answering the substitution question. The ground screw load-test planning guide separates investigation, qualification, proof and production purposes; use that distinction when deciding what must change.

The IEA PVPS report on technical risks in PV power systems describes mounting failures associated with ground conditions, weak anchorage, inappropriate materials and installation errors. These portfolio-level observations support reopening relevant checks; they do not decide a particular substitution.

Propagate the Change Beyond Foundation Calculations

A technically reviewed substitution can still fail through stale project information. Build a propagation matrix that names every affected deliverable, owner and release state. Do not assume the foundation designer will automatically update procurement, civil works, quality and field documents.

Freeze affected releases until the propagation owner confirms the impact. Do not amend a purchase order from a meeting note while design remains provisional, or let design approval silently authorize changed sources, equipment, testing or permits.

ISO 10007:2017 guides configuration management from concept to disposal. Apply that principle through one authorized baseline, visible change status and traceable consistency between requirements, product identity, documents and installed population. This does not claim ISO certification.

Qualify the Replacement Through a Stage Gate

The substitution should move through bounded gates rather than one blanket approval. Each gate has a permitted purpose and a prohibition. Approval to seek a quotation is not approval to manufacture; approval to test prototypes is not approval to install production units.

A practical gate set is:

1. Request accepted for review: reason, identities, locations and decision date are complete.
2. Design route accepted: responsible parties define required analysis, investigation, evaluation and testing.
3. Candidate frozen: product, source, head, installation system and evidence revisions are controlled.
4. Qualification released: only the named test population proceeds under the approved method.
5. Production released: results pass, exceptions close and downstream documents are current.
6. Change closed: installed population, records, approvals and as-builts reconcile to the replacement.

At every gate, state the population and expiry. A release for one trial location, soil zone or product length cannot migrate elsewhere by convenience. If observations leave the approved envelope, return to the appropriate earlier gate.

Close One Foundation Substitution Decision Record

The final record should let an independent reviewer reconstruct why the change was proposed, what was compared, which evidence survived, what was redone, who decided and which foundations are covered. Include the classification; before/after configuration sheets; location map; input revisions; calculations; durability route; product reports; evaluation applicability; load tests; installation method; ITP and logs; deviations; approvals; commercial authorization; and as-built mapping.

Add an evidence carry-over index showing every earlier document and its outcome: retained without technical change, retained after stated verification, superseded, or not applicable. A superseded calculation or drawing should remain traceable as history but should not appear current in the site pack. Record open residual actions and the authority responsible for each.

The decision must identify the accepted system/revision, zones, installation and test conditions, monitoring, exclusions, revalidation triggers and changed documents. If the evidence burden cannot be met, rejection is a valid controlled result.

Changing only the manufacturer within a selected screw-pile concept has a narrower workflow; see Screw Pile Manufacturer Changes. Checking whether one report covers one proposed helical product is handled in Helical Piles Evaluation Report Applicability. A ground screw–helical pile system substitution can contain both questions, but it cannot be closed by either one alone.

The governing principle is simple: carry requirements forward, not conclusions. Reuse factual site data only within confirmed limits, preserve current project criteria, and rebuild the product-specific design and evidence wherever the foundation system changes what those records represent.

Related Resources

• Ground Screw vs Helical Pile: Initial Selection by Evidence
• Screw Pile Manufacturer Changes
• Helical Piles Evaluation Report Applicability
• How to Plan a Ground Screw Load Test Program
• Screw Piles and Ground Screws

References

• ASCE MOP 162 (2026) — Design and Construction of Solar PV Structures
• ICC-ES AC358 — Helical Pile Systems and Devices
• ICC-ES — What’s in an Evaluation Service Report
• ISO 10007:2017 — Guidelines for Configuration Management
• IEA PVPS T13-23:2021 — Quantification of Technical Risks in PV Power Systems

Next Step: Submit One Proposed Substitution

Send the current and proposed foundation drawings and product identities, project zone map, geotechnical information, structural reactions and movement criteria, current calculations, evaluation or certification records, load-test information, installation method, durability basis, affected approvals and required decision date through Screw Piles or to info@baolaipipes.com. East Baoyu can help organize supplier-side configuration, manufacturing, interface and inspection evidence for the agreed inquiry scope. The appointed geotechnical and structural designers, owner, installer, test authority, inspector and authority having jurisdiction retain their assigned design, testing, safety, approval and final-acceptance responsibilities.