Ground Surface Effect of Earth Pressure Balance Tunnelling in Deltaic Deposits: A Case Study of Line 9 of the Barcelona Metro

Abstract

The 47.8 km long Line 9 of the Barcelona Metro is one of Europe’s longest urban metro lines. Its southern section connects the city to the airport, being entirely excavated through soft deltaic deposits, promoting more sustainable mobility by reducing significant road traffic. This study identifies the most accurate method for predicting surface settlements caused by tunnel excavation using ground movement monitoring data. Several methodologies were assessed, with the Mean Absolute Error (MAE) and Mean Relative Error (MRE) calculated to evaluate their performances. The methods considered were Peck’s Gaussian curve method, Sagaseta’s method, and Verruijt and Booker’s method, with MAE values of 0.66 mm, 0.50 mm, and 0.48 mm and MRE values of 49%, 45%, and 36%, respectively. Verruijt and Booker’s method proved the most effective for predicting settlement, minimising surface impacts, improving building sustainability, and reducing environmental contamination from chemical injections. A sensitivity analysis was also conducted by comparing the monitoring data from Line 9 with data from 45 other tunnels excavated worldwide in deltaic soils. This analysis aimed to develop rapid predictive models applicable to different locations. The methodologies proposed for estimating ground settlements relied on specific parameters, particularly the K value, which was consistent across all deltaic soil locations, with values ranging from 0.45 to 0.55.