A simple algorithm for predicting the maximum surface settlement considering support mechanisms of shield tunneling

Accurate prediction of ground surface settlement is essential in urban shield tunneling projects to prevent damage to nearby structures. While empirical and data-driven models have been widely used, they often neglect support mechanisms such as grouting and slurry injection, or require extensive datasets that are not always available to obtain promptly. This study proposes a simple and practical algorithm for predicting the maximum surface settlement induced by shield tunneling. The algorithm was developed using the parametric results from three-dimensional numerical modeling of the excavation and support process of shield Tunnel Boring Machines (TBMs). The results indicated that the stiffness of the weaker support material plays a dominant role in controlling settlement, particularly when the face pressure is maintained above the active earth pressure. For the purpose of incorporating the effects of support mechanisms, three gap parameters were defined at the tunnel face, shield annular gap, and tail void, and were modified based on stress states and support stiffness. Correction coefficients were introduced to quantify the contribution of each support phase at specific ground type. The proposed algorithm requires only a limited number of input variables, such as ground properties and face pressure, making it suitable for field application. The model was validated against field measurements with prediction errors within 2 mm. This study provides a physically grounded and computationally efficient framework that improves predictive accuracy while addressing limitations of traditional methods in shield tunneling settlement analysis.