As part of the integration of the N21 Martigny – Grand-Saint-Bernard section into the national road network in 2020, the Federal Roads Office (FEDRO) launched a minor structural maintenance programme (KBU) aimed at preserving the condition of engineering structures until the next major rehabilitation interventions. These measures are intended to halt deterioration processes and prevent more extensive interventions in the future.

Exposed to demanding climatic conditions and affected by limited maintenance in the past, the road section has an overall condition requiring significant works on its bridges, retaining walls and galleries.

Within the framework of the NEB Valais N21/N06 project development mandate, INGPHI participated in the condition assessment of the structures, the definition of intervention measures and their prioritisation. Given the large number of structures concerned and the length of the section, major maintenance interventions are planned over an approximately ten-year period between 2025 and 2035.

In parallel, the Territorial Unit III Service (SUT III) appointed INGPHI for the planning and monitoring of the minor structural maintenance measures implemented on the N21 structures.

Since 2022, several work campaigns have been carried out on the structures along the section through targeted interventions. The main achievements include:

2022: An initial intervention was carried out on the Lavanchy Bridge, involving local deck repairs following an impact caused by rockfall.

2023: A major work campaign covered eleven structures along the section. The interventions mainly involved the rehabilitation and replacement of expansion joints, refurbishment of waterproofing systems and pavements adjacent to the joints, as well as modifications to certain structures, including the removal of expansion joints, in order to improve durability and reduce future maintenance requirements.

2024: Works continued with the replacement of bridge bearings and the rehabilitation of bearing seats on the Trappistes Bridge. Detailed investigations were also carried out on the Pont-Sec 254 retaining wall to assess its behaviour and define the necessary strengthening measures. A monitoring system using inclinometers was installed.

2025: Interventions concerned several structures along the section, including the replacement of expansion joints, rehabilitation of abutments and masonry elements, renewal of safety equipment, as well as strengthening and local repair works on existing structures.