Eurocode 7 and Ground Screws: What the standard says about foundation design using screws

Eurocode 7 (ČSN EN 1997) is the European standard for geotechnical design, which also applies to foundations on ground screws (screw piles). If you are planning a PV plant, timber-frame building or industrial structure and are considering ground screws as an alternative to concrete, Eurocode 7 is the document that both the designer and the building authority will refer to.

This guide explains what the standard requires, how this applies to working with a screw-driving machine, and what it means in practice for an EPC contractor.

What is Eurocode 7?

Eurocode 7 (EN 1997-1 and EN 1997-2) forms part of the Eurocode series of European standards for structural design. Part 1 covers general rules for geotechnical design, while Part 2 deals with ground investigation and testing.

It is implemented in the Czech Republic as BS EN 1997-1 a EN 1997-2. Since 2010, it has replaced the older national standards for foundation engineering.

Key areas for ground screws:

Geotechnical categories (GK1–GK3) — which surveys are compulsory
Design approaches (DA1, DA2, DA3) — how to calculate the ultimate bearing capacity
Requirements for pile foundations (Section 7) — direct basis for the calculation of ground screws
Testing and monitoring — when a trial pile is necessary

How does Eurocode 7 classify screw piles?

Ground screws (screw piles, English screw piles or helical piles) are classified in Eurocode 7 in the category piled foundations (pile foundations). Section 7 of EN 1997-1 applies to them.

Specifically, the following are relevant:

§7.4 — Vertical bearing capacity of piles — calculation of the ultimate bearing capacity based on soil geotechnical parameters
§7.5 — Horizontal bearing capacity of piles — relevant to wind-loaded structures (PV systems, carports)
§7.6 — Pilot testing — when static or dynamic load testing is necessary
§2.8 — Geotechnical categories - determines the scope of the survey

Geotechnical categories and what it means in practice

Eurocode 7 divides projects into three geotechnical categories (GC) according to complexity:

Category	Typical projects	Requirements
GK1	Simple structures, unified conditions, PV systems on flat terrain	Minimum research, experience is enough
GK2	Standard buildings with a certain complexity of terrain, industrial halls	Routine geotechnical investigation + calculation
GK3	Unusual conditions, unstable slopes, heavy loads	extensive site investigation, specialist geotechnical engineer

The vast majority of projects using ground screws (PV plants 1–10 MWp, timber structures, industrial halls on standard soil) fall under GK1 sky GK2. That means a geotechnical site investigation comprising 1–3 boreholes at the location and a standard bearing capacity calculation.

Design approach DA1 — how bearing capacity is calculated

The Czech national annex to EN 1997-1 prescribes design approach DA1, combinations 1 and 2, for piles:

DA1 Combination 1 (DA1/1): load × 1.35/1.5, geotechnical parameters without reduction → deformation is assessed
DA1 Combination 2 (DA1/2): unreduced load, geotechnical parameters × 1.25 → ultimate limit state is assessed

For ground screws in practice, this means: the designer needs the soil shear strength values (φ, c) from a geotechnical investigation, typically CPT tests or borehole investigations with SPT tests.

Based on this data, it is calculated characteristic load-carrying capacity of the screw R_k and it is verified whether the resulting design load-bearing capacity R_d = R_k / γ_t exceeds the design load.

For a PV plant project in normal loamy-sandy soil without anomalies, this calculation generally demonstrates sufficient load-bearing capacity for 76–110 mm diameter ground screws.

When is a probationary period required?

Eurocode 7 §7.6 sets out the conditions for mandatory pile load testing. For screw piles, the following are particularly relevant:

A test pilot is recommended or required if:

The project is in complex geotechnical conditions (GK3)
It is not possible to reliably determine the soil resistivity by calculation from the available data
This is a high-risk project (bridges, high-rise buildings)
The investor or insurance company requires proof of bearing capacity by measurement

A test pilot is generally not required if:

GK1 or GK2, standard soil, investigation carried out
PV system project or light industrial building with low loads
There is experience with similar projects at the site (reference pilots).

In practice: for a typical PV plant up to 10 MWp on flat terrain in the Czech Republic, a test pilot must not as a rule be dispensed with — but it depends on the specific soil. Test drilling of the first 3–5 screws with torque measurement is a standard procedure that most driving machines (including Glentor B80 a Glentor C65) enables this thanks to the recording of data from the telematics unit.

Machine certification vs. base certification

Eurocode 7 deals with the design and verification of foundations, whereas CE marking addresses machine safety. CE certification of a driving machine confirms its safe operation, not the bearing capacity of the installed foundation. The bearing capacity of a pile or ground screw must always be assessed separately in accordance with the geotechnical and structural requirements of the given project.

The bearing capacity of the foundation is proven by:

By geotechnical site investigation (boreholes, CPT probing, laboratory tests)
By structural calculation per EN 1997-1 (to be prepared by the designer)
By the installation protocol — recording of the moment and depth of each screw (machine telematics)

Glentor B80 i Glentor C65 they are equipped with a telematics unit that records the torque curve during screwing. This record serves as proof of achieving the geotechnical resistance at each point — a key document for both the designer and the building authority.

What this means for EPC contractors: a practical checklist

If you are building on ground screws and the project is subject to planning permission, you typically need:

Geotechnical investigation (scope per GK — typically 1–3 boreholes/CPT probes)
Structural calculation according to ČSN EN 1997-1 (to be prepared by an authorised geotechnical engineer)
Certification of the screws as a product (ETA or compliance with EN 14199)
CE machine certification document (boring machine complies with 2006/42/EC)
Installation logs from machine telematics (torque × depth at each point)
Building permit or notification according to the local building authority (depends on the project)

For PV plants and light industrial buildings on standard soil, the entire process can usually be managed within a matter of weeks and does not require non-standard measures.

EN 14199 — standard specifically for grouted anchors

In addition to Eurocode 7, there is also EN 14199:2015 (Execution of special geotechnical works — Micropiles), which applies to micropiles and screw piles. This standard specifies:

Material and workmanship requirements
Installation logs (monitoring)
Acceptance tests

EN 14199 complements Eurocode 7 at the performance level — while EC7 specifies what is to be achieved, EN 14199 states how it is to be carried out. Both documents are relevant for projects where the foundation documentation is part of the planning permission.

Frequently Asked Questions

Must every ground screw project have a geotechnical survey?
For GK1 projects (simple structures, PV systems on standard soil), the designer can base their work on available data (geological map, local experience). For GK2 and above, an investigation is mandatory. In practice, we always recommend carrying out at least a trial installation of the first 5 ground screws with a torque record.
Does Czech building administration recognise ground screws as fully-fledged foundations?
Yes. Ground screws are a recognised foundation method in the Czech Republic in accordance with ČSN EN 1997. Any refusal by the building authority is non-standard and is usually based on inadequate documentation, not on a principled ban.
Is an ETA (European Technical Assessment) required for ground screws?
The ETA applies to the product (screw as a structural element), not the machine. For standard installation, compliance of the screw with EN 14199 or an ETA issued by the screw manufacturer is sufficient. The driving machine as such does not need an ETA — it is CE certified as machinery.
What to do if the building authority rejects ground screws?
As a rule, it is a matter of insufficient documentation. The solution is: to supplement the geotechnical investigation, submit a structural calculation from an authorised geotechnical engineer, and provide installation records from the machine's telematics. In the event of persistent refusal, an opinion may be requested from ČKAIT.

Where to continue

Technical comparison of ground screws and concrete in terms of costs, speed and ecology: Ground screws vs concrete foundations

What driving machine do you need for your project: Glentor B80 for standard conditions, Glentor C65 for demanding terrain with a hydraulic breaker.