Inter IKEA Bayonne

Engagement scope

• 3D Soil-Structure Interaction analysis across all four building blocs
• Site-specific seismic response under post-2011 Eurocode 8 (NF EN 1998-1) framework
• Liquefaction susceptibility assessment for the Adour-floodplain alluvium
• Deep-foundation verification — coordination with the foundations specialist's pile design
• Thermomechanical analysis of long-span retail roofs
• Multi-pass design optimisation — re-engagement once the as-built foundation system was finalised
• Synthesis notes feeding the design office's simplified verification calculations across the remaining blocs

Why this engagement mattered

On a coarse European hazard map, southwest France looks unremarkable. The country sits in the moderate-to-low band of the EU-wide seismic catalogue, and the popular intuition for retail underwriters places "real" earthquake exposure somewhere south of the Pyrenees. That intuition is wrong, and Bayonne is exactly the kind of postcode where it breaks.

France's 2010 zoning revision (formalised into building codes in 2011) reclassified the western Pyrenees-Atlantiques as zone 3 — sismicité modérée. From that point onward, any new commercial structure of normal or higher importance had to be designed under Eurocode 8, with full site-specific consideration of the underlying soil. The Inter IKEA Bayonne retail park — anchored by IKEA itself, with Primark taking the largest secondary block and the remaining tenants spread across three more blocs — was one of the first large-format retail developments in France to land under that new regime.

The complication is geological. The site sits on the alluvial plain of the Adour, the river that drains the western Pyrenees into the Bay of Biscay. The soil column that underlies the park is not the kind of rock-like substrate where a generic spectral coefficient is good enough; it is a layered sedimentary deposit with the kind of properties that demand 3D Soil-Structure Interaction — a method usually reserved for nuclear plants, large dams and acute-care hospitals, not retail.

What was actually delivered

Dynamis ran the seismic engineering across the entire forum commercial — four independent building blocs of varying mass, height and tenant fit-out, all within a single 200 m × 200 m footprint plus an 18,800 m² external parking apron.

The engagement was structured in two phases. The 2013 phase, contracted through Oger International as principal contractor, established the seismic design basis: full 3D SSI for each bloc, a dedicated liquefaction note for the Adour-floodplain stratigraphy, pile-foundation verification, and a thermomechanical study of the long-span retail roofs. The deliverables included a master note de synthèse consolidating the results so that the architects' design office could perform simplified per-bloc verifications without re-running the 3D model on every minor revision.

The 2014 phase, contracted via Franki Fayat — a specialist deep-foundations contractor — re-validated the seismic response of three blocs (including the Primark anchor) once the as-built pile system had been finalised. The deeper, more flexible foundation that Franki Fayat actually drove into the ground behaved differently from the baseline assumed in the original design: the additional flexibility at the soil–structure interface reduced the seismic demand transmitted into the superstructure. That kind of correction is invisible to a generic vulnerability curve. It only shows up when the seismic engineer and the foundations specialist co-design.

What this means for portfolio risk

For a (re)insurer underwriting commercial real estate in Western Europe, three observations from this engagement matter more than any single number:

1. "Low-seismic France" is a coarse category. Beneath that average, there are sites where the prevailing soil class drives the design entirely. The Bayonne case is one. Coarse cat-model maps that resolve at country or NUTS-2 region level cannot see this — they smooth across the Adour floodplain and the surrounding limestone hills as if they were the same exposure.
2. Aggregation in one footprint is a tenant-correlated BI exposure. Four blocs on a single 4-hectare plot, anchored by two of the most recognisable retail tenants in Europe, mean that a single ground-shaking event correlates the BI losses across the whole park. The PD/BI severity distribution for this asset is not the convolution of four independent retail boxes; it is dominated by the joint distribution.
3. Engineering-informed foundations move the loss curve. The 2014 re-engagement showed an as-built foundation that reduced design seismic demand once the actual pile flexibility was modelled. A vulnerability function calibrated on generic European retail boxes assigns the wrong damage ratio to this asset — almost always biased high for a well-engineered park, almost always biased low for one engineered to code minima with no SSI.

From engagement to portfolio indicators

Every project of this calibre — engineered to perform, not just to comply — becomes evidence in the engine that powers Xpectral. The 3D Soil-Structure Interaction model from a retail park on the Adour floodplain is not an isolated deliverable: it calibrates the hazard model and, more importantly for our roadmap, it informs the engineering-grade fragility curves we are now building.

Fragility curves today are built on simplified assumptions. Ours are built on 15 years of designing structures that cannot fail. By embedding performance-based seismic design into AI-driven models, we transform fragility from generic to engineering-grade.

— Carlos Caramés Molero, Founder & Partner, Dynamis

That difference does not stay academic. It propagates straight into the indicators (re)insurers actually price on: PML for catastrophe risk capital, AAL for technical premium, EP curves for accumulation control, SCR for Solvency II capital efficiency. Generic vulnerability functions cannot tell the difference between a code-minimum retail box and an engineered park with as-built foundation flexibility. Ours can — because we engineered both.

Sources & references

1. Dynamis project portfolio: dynamisassociates.com
2. Inter IKEA Centre Group, retail park development programme (public corporate communications, 2013–2014).
3. French seismic zoning, Décret n° 2010-1255 du 22 octobre 2010; Eurocode 8 (NF EN 1998-1) application to French commercial structures, mandatory from 1 May 2011.
4. Internal Dynamis design archive: 2013 engagement (Oger International) and 2014 engagement (Franki Fayat) — confidential, not public.