New foundation techniques around existing towers

Context

As Belgium’s electricity grid evolves, Elia needs to reinforce and upgrade existing high-voltage overhead lines to increase transmission capacity and support the electrification of society. In many cases, this requires replacing existing pylons with new structures that can withstand higher voltage levels and larger mechanical loads.

Today, this type of one-for-one replacement generally requires a long outage. The existing conductors must first be dismantled, after which the pylon and its foundations are removed. New foundations are then built, with concrete drying alone typically requiring around 27 days, before the new pylon and conductors can be installed.

This approach creates operational constraints, especially as the number of grid reinforcement projects continues to increase and long-duration outages become more difficult to secure. Reducing outage requirements could therefore help accelerate grid delivery, limit congestion risks and improve security of supply.
The New Foundation Technique project investigates whether new foundations can be designed and built around an existing pylon while it remains in service. The main objective is to minimise or avoid outage periods during the foundation phase, while maintaining the stability of the existing structure and preparing the site for the future pylon.

Approach

The initial concept was inspired by practices already used by other transmission system operators. The idea was to integrate micropiles into or around the existing foundation and mechanically connect new stubs to increase stability. In this configuration, the future tower loads would largely be transferred through the micropiles and welded stubs, reducing excavation needs and preserving the stability of the existing structure.

However, applying this approach to Elia’s context is more complex. The future pylons considered for Belgian grid upgrades, particularly standardised 380 kV structures, are subject to significantly higher mechanical loads than those for which the existing solution was designed. In addition, the footprint of the new pylon may be much larger than that of the existing one, whereas the initial concept is limited when the difference between both footprints remains very small.

The project therefore shifted from searching for one universal solution to developing a portfolio of technical solutions. These solutions will depend on four main parameters: the geometry of the existing and future pylons, the available space for civil works and machinery, the soil conditions, and the mechanical loads of the future structure.

Results

The first investigations have already provided an important insight: the initial micropile-based concept is not directly transferable to Elia’s main use cases.

This conclusion does not close the opportunity. On the contrary, it refines the scope of the project.

The focus is now shifting towards a portfolio of technical solutions, with each option depending on key parameters such as tower geometry, soil conditions, available working space and mechanical loads.

Next steps

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