Analysis of post-ground settlement induced during twin tunnelling in silty sand

As metro lines continue to expand rapidly in urban areas, the excavation of twin tunnels in shallow depths using shield tunnelling methods has become widespread. By analysing field data obtained from an actual shield tunnelling project, it has been observed that the post-ground settlement occurring over the preceding tunnel during the excavation of the following tunnel in silty sand is approximately 42% of the green field settlement, which cannot be disregarded. Accurate approximation of the post-ground settlement is useful for preventing any damage due to excessive deformation and to determine the total ground settlement profile during twin tunnel construction stage. And yet, only a few number of studies have focused on investigating and predicting the post-ground settlement that occurs during twin tunnel construction in soft soils. Therefore, this study develops a transparent model using the multi-gene genetic programming (MGGP) method, enabling the prediction of post-ground settlement during twin tunnelling. Comparative analysis demonstrates that the proposed model is user-friendly and capable of generalising to unseen data. The reliability of the MGGP-based model has been validated through sensitivity and parametric analyses. Additionally, when estimating post-settlement during twin tunnelling, it is essential to consider the spacing between twin tunnels, soil cohesion, and crucial operational parameters of the shield, such as torque and face pressure.