Undrained stability of wide rectangular subsea tunnels using finite element limit analysis and multivariate adaptive regression splines

The construction of subsea tunnels for transportation infrastructure has experienced significant growth in recent decades. Consequently, ensuring the face stability of these tunnels is critically essential. This study employs finite element upper bound and lower bound analyses to determine the necessary retaining pressure to avert collapse in wide rectangular subsea tunnels, considering various geometrical and mechanical parameters. Unlike previous studies that focused on rectangular tunnels in conditions where the water table is below the ground surface or circular subsea tunnels, this work addresses the unique challenges posed by wide rectangular tunnels under subsea conditions. The analysis was conducted under plane strain conditions, assuming the soil adheres to the Tresca failure criterion. The findings indicate that the required normalized retaining pressure increases with the ratios of water depth, soil cover, and tunnel width relative to tunnel height. The difference between the finite element upper bound and lower bound solutions was so close that their relative error never exceeded 3%. The multivariate adaptive regression splines (MARS) method was implemented to obtain a correlation between input and output dimensionless parameters. The statistical measures showed that MARS was highly capable of predicting the required retaining pressure.