General presentation
The NF P 94-500 standard (November 2013 revision) defines the content and sequence of geotechnical engineering missions in France. It has contractual value and has become, with the ELAN law of 23 November 2018, a virtually mandatory reference for any construction operation: a preliminary G1 geotechnical study is required before the sale of undeveloped land intended for a single-family house in zones of medium or high clay shrink-swell hazard.
The standard distinguishes five main families of missions which follow one another from the start of design through to construction, and even beyond.
The five geotechnical missions
| Mission | Project phase | Purpose |
|---|---|---|
| G1 — Preliminary geotechnical study | Preliminary studies & sketch | Identify the main geotechnical risks of the site. Subdivided into G1 ES (Site Study) which characterizes the site and identifies the hazards, and G1 PGC (General Construction Principles) which proposes suitable construction principles. |
| G2 — Geotechnical design study | Preliminary design / detailed design / tender | Detailed design study, defining the geotechnical assumptions and sizing the structures. Subdivided into G2 AVP (preliminary design), G2 PRO (detailed design), and G2 DCE/ACT (tender documents / works contract assistance). |
| G3 — Geotechnical execution study & monitoring | Execution & construction | The contractor's mission. Study of execution methods then monitoring during the works. Checks compliance with the G2 assumptions. |
| G4 — Geotechnical execution supervision | Execution & construction | The client's or project manager's mission. Supervises the contractor's G3, validates adaptations. |
| G5 — Geotechnical diagnosis | Any phase | One-off study of a specific geotechnical element (disorder, expert appraisal, diagnosis of an existing structure). Independent of the G1-G4 sequence. |
Typical sequence on a project
Upstream phase → G1 ES (site characterization) → G1 PGC (construction principles)
Design phase → G2 AVP → G2 PRO → G2 DCE/ACT
Construction phase → G3 (contractor) ⇄ G4 (client / project manager)
Outside the sequence → G5 for a one-off problem or diagnosis
Which client commissions what?
| Party | Missions to commission |
|---|---|
| Client (owner) | G1, G2, G4 (and G5 if needed) |
| Works contractor | G3 (included in its offer) |
Why a geotechnical study?
A geotechnical study compliant with NF P 94-500 protects the client by providing:
- a reliable knowledge of the ground before any financial commitment
- a suitable design of foundations and geotechnical structures
- legal security (mandatory mention in the sale agreement in shrink-swell zones)
- cost control (anticipating risks rather than correcting disorders)
In more than half of construction disorders, the absence or insufficiency of the geotechnical study is at fault. As an example, the shrink-swell hazard alone represents several hundred million euros per year.