Overview

Swissgrid manages more than 6,700 kilometres of 380/220 kV lines and 12,000 pylons. The company is an expert in its field and has mastered the construction and maintenance of ultra-high-voltage lines in Switzerland. Most of them cross natural hazard zones. The hazard zones along the Chamoson – Chippis line are known and listed by the Canton of Valais. In the Swiss Federal Office of Energy’s approval for the line from 2010, one requirement was for Swissgrid to determine measures to be applied for the construction of pylons situated in natural hazard zones, in collaboration with the cantonal geologist. Based on the new cantonal directive relating to the establishment of hazard zones and corresponding construction permits, the cantonal geologist demanded an additional natural hazards study for the Chamoson – Chippis ultra-high-voltage line project, specifically between pylons 121 and 173. .The company BEG was tasked with undertaking a further study, the results of which were presented to the cantonal geologist by Swissgrid in 2016.

Managing the risks linked with such hazard zones is the focus of Swissgrid’s endeavours. Numerous engineers from different areas have been at work for years already, studying these specific measures, which have been known for some time.

In these zones, Swissgrid is currently collaborating with the cantonal geologist and specialists in geotechnical studies with the goal of applying specific protection measures for each type of hazard.

Types of hazards

Below are the main types of natural hazards listed by the canton of Valais along the route of the Chamoson – Chippis line.

Danger of land movement

Ground instability is characterised by the risk of ground movement. This encompasses several phenomena such as landslides, falls and collapses.

Danger of rock falls

The term rock fall refers to any sudden fall of rocks or isolated blocks from a mountain. These blocks usually become detached due to weaknesses in the rock. The type of soil and geological structure play an important role in the consideration of this type of risk. The chalkier the rock, the more crumbly it tends to be. The danger of rock falls is also influenced by meteorological conditions and climate. Rock falls notably tend to increase with heavy rain.

Danger of debris flow

Debris flow is characterised by a mixture of water and solid materials swept along, , such as sand, gravel, rock and even wood. This phenomenon arises when the sediment content nears or exceeds that of the water flowing, rendering it thicker and more granular. This spectacular mass can exceed two tonnes per square metre.

Interactive map of natural hazards in the Valais

The Cantonal Office for Forests, Waterways and Landscape (SFCEP) publishes an interactive map of the natural hazards listed by its departments for the public.

Protective measures for the Chamoson – Chippis line

In every powerline construction project, Swissgrid must meet very precise risk management criteria. With this in mind, the company relies on recognised experts and technical studies to validate the feasibility and to realise the projects.

In the case of the Chamoson – Chippis line, Swissgrid is depending on several rigorous technical studies, recognised by experts and the law. Each natural hazard zone crossed by the line is listed and monitored by the Canton of Valais and its respective departments. Detailed planning per pylon is carried out in order to define and ratify the construction parameters. As each pylon is erected on a different type of surface, it is essential for Swissgrid to understand the environment in which it will be constructed perfectly.

This process allows specific technical protection solutions to be defined for each natural hazard zone. Moreover, Swissgrid is collaborating with the municipal authorities and the Canton of Valais in the application of technical protection measures for several pylons in natural hazard zones. In these cases, the goal is to identifie extended joint solutions that will enable the protection of not only the pylons but also cantonal and municipal roads, industrial zones and homes.

List of potential protection measures

Against land movement

Placement of one to four ground measuring devices (inclinometers) per site. Based on the data collected over a period of a year up to 18 months, the potential adaptive measures will be defined, including:

• Reinforcement of foundations
• Deepening of foundations
• Securing of pylon feet through reinforced concrete girders

Against rock falls

• Placement of rock fall protection netting

Against debris flow

• Construction of a dyke

Furthermore, ground repair work was carried out following the storms of the winter of 2017/2018. Log caissons were installed below the foundations and the footpath above the pylon was secured with a wooden barrier.

These measures were part of the additional study realised by BEG at the request of the cantonal geologist and were implemented with the latter’s help.

Due to the construction measures implemented by Swissgrid, the pylon has not moved since it was installed in the spring of 2017.