Analysis of Local Settlements Due to Operational EPB Tunneling Driving Parameters: A Case Study of the Barcelona Metro Line 9 Tunnel

Line 9 of the Barcelona Metro crosses beneath the Llobregat and Besòs Rivers, requiring tunneling through soft deltaic deposits of Holocene age. The excavation was carried out using Earth Pressure Balance (EPB) Tunnel Boring Machines (TBMs), a method commonly employed in urban environments to control ground movements and minimize settlements. This study analyzes the ground response to EPB tunneling, focusing on key factors such as TBM operational parameters (face pressure, shield pressure, etc.), grouting techniques, and the influence of shaft entry/exit points, hyperbaric stops, tool wear, and the learning curve. Additionally, secondary influences, including variations in cover depth and the presence of lightly compacted made ground, were found to exacerbate ground movements. Field data collected from Section 1 of Line 9 provide a detailed assessment of settlement patterns and ground behavior. Results indicate that, while EPB TBMs generally maintain ground stability with minimal settlement (with average volume losses below 0.5%), certain site-specific challenges, such as inconsistent grouting and shaft transitions, led to localized volume losses and settlement. This paper contributes to refining predictive models of ground–structure interaction in soft ground tunneling, offering insights to optimize future EPB operations in similar geological conditions, ensuring more effective control over ground movements and settlement mitigation.