Foundations on paved surfaces (asphalt, paving, concrete) — standards and requirements

The installation of ground screws on paved surfaces—asphalt, paving or concrete in car parks and garages—is governed in EU by Eurocode 7 for subgrade geotechnics beneath the roadway and Eurocodes 1 and 3 for loads and the structure of the above-ground building (carport), while the composition and quality of the roadway itself are assessed according to national pavement catalogues, which are not harmonised within the EU.

Three levels that need to be distinguished

Foundations on a paved surface combine three separate areas, which in practice are often dealt with by different specialists:

  1. Subgrade geotechnics — is dealt with by Eurocode 7, just like for foundations on a greenfield site
  2. Composition and condition of the road surface itself (asphalt thickness, base layers, their bearing capacity) — dealt with by national pavement catalogues, not Eurocode
  3. Design and load of the carport over the roadway — covers Eurocode 1 (actions) and Eurocode 3 (steel structures)

The investor and the designer need to coordinate all three areas — the geotechnical survey must also include the pavement composition, not just the soil beneath it.

Eurocode 7 — geotechnics beneath the pavement

A general overview of the standard can be found in a separate article: Eurocode 7 and ground screws. For construction over a paved surface, the following are also relevant:

The survey must include the pavement layer. Geotechnical investigation for a carport in a car park includes not only the soil at the depth of the screw pile, but also the composition of the pavement itself (thickness of the asphalt, underlying gravel layers) — without this information, the drilling procedure cannot be properly designed.

Group effect and screw spacing. Eurocode 7 requires the bearing capacity of a group of piles (including screw piles, if they are designed as pile foundations) to be assessed, in particular the possibility of block failure or interaction between individual elements.

Documentation for the site operator. Recording of installation parameters (e.g. achieved torque and installation depth) can serve as part of the quality assurance documentation for the designer, investor or site operator.

Pavement structure — national catalogues, not Eurocode

Unlike subgrade geotechnics, there is no harmonised European standard for the design and assessment of pavement structures. Each country uses its own pavement catalogue:

Czech Republic Technical Specifications TP 170 (Design of Road Pavements) — determine the thickness and composition of asphalt and base layers according to the traffic load of the area.

Germany: RStO 12 (Guidelines for the Standardisation of Pavement Structures) — German standard for pavement structure design.

Austria: RVS 03.08.63 – Austrian guideline for pavement design.

France LCPC-SETRA Technical Guide for Pavement Design.

Poland: Catalogue of typical pavement structures — the Polish catalogue of typical road pavement structures.

Practical impact: Prior to execution, it is necessary to determine the actual pavement structure on the specific area (car park project documentation, or trial pits) — without this information, it is impossible to determine whether a DTH pilot hole is required and at what depth.

Eurocode 1 — Carport loading

EN 1991 (Eurocode 1: Actions on structures) specifies how a carport, as an elevated structure with a large wind-exposed area, differs from a low-level PV mounting system on the ground:

Wind. A carport has a higher wind exposure than a ground-mounted PV structure — the loading is calculated in accordance with EN 1991-1-4, including the exposure factor for the given height and surrounding development (open car park vs. sheltered location between buildings).

Buoyancy. The flat roof of a carport can generate uplift forces under certain wind directions, which the screw and anchorage detail must be able to withstand — this load is practically irrelevant for a ground-mounted PV structure.

Snow. In locations with relevant snow load, it is included in accordance with EN 1991-1-3, in combination with wind according to EN 1990.

Eurocode 3 — steel structure

The supporting structure of the carport (posts, purlins, frame under the panels) is typically made of steel or aluminium and is designed in accordance with EN 1993 (steel) or EN 1999 (aluminium). The connection detail between the post and the ground screw head is crucial — it must transfer the combination of vertical load, horizontal wind load and uplift.

Specifics of anchoring into hard surfaces

DTH pre-boring. For thicker asphalt surfacings or compacted base layers, it may be appropriate to use a DTH pre-bore or another pre-boring technology depending on the nature of the subgrade.

Local surface repair. After screwing in, the area around the screw is finished — with a sealant for asphalt, and by replacing the paving blocks around the screw head for paving. The scope of the intervention is an order of magnitude smaller than for a concrete foundation with excavation.

Coordination with operations. Execution in an operational car park requires temporary marking, sector clearance and frequently night work — this is an organisational, not a normative requirement, but it affects the project schedule.

Checklist pro zakládání carportu na zpevněné ploše

  • Geotechnický průzkum vč. skladby vozovky (tloušťka asfaltu, podkladní vrstvy)
  • Ověření skutečné skladby dle národního katalogu vozovek (TP 170, RStO 12 apod.)
  • Statický výpočet zatížení dle EN 1991 (vítr, vztlak, případně sníh) a EN 1990 (kombinace)
  • Návrh ocelové/hliníkové konstrukce dle EN 1993 / EN 1999
  • Rozhodnutí o nutnosti DTH předvrtu dle tvrdosti podkladu
  • Plán koordinace s provozovatelem plochy (značení, sektorování, noční práce)
  • Telemetrický záznam instalace pro každý vrut
  • Plán lokální opravy povrchu kolem každého bodu

Frequently Asked Questions

Where to continue

Jak prakticky probíhá instalace solárního carportu na zemních vrutech: Solární carporty na zemních vrutech

Obecný přehled geotechnického navrhování dle Eurocode 7: Eurocode 7 and ground screws