ABSTRACT
The Eryri Visual Impact Provision (VIP) project, promoted by National Grid, aims to reduce the visual impact of electricity transmission infrastructure in the Eryri National Park, North Wales UK. The project involves replacing overhead lines and pylons crossing the Dwyryd Estuary with underground electricity cables housed in a 3.3km long, 3.5m internal diameter tunnel. The Garth Launch Shaft serves as a key component, used to launch the Tunnel Boring Machine (TBM) and providing access for supporting cable installation and maintenance. A three-dimensional finite element analysis, using PLAXIS 3D, was conducted to simulate the construction phases and examine Soil-Structure Interaction (SSI). This analysis provided crucial insights into the behaviour of temporary and permanent support systems, guiding the design of the Garth Shaft. The paper highlights the benefits of SSI analysis and its role in understanding the interaction between temporary supports and the permanent structures.
