Numerical investigation and prediction of the excavation face stability for river-crossing shield tunneling: An intelligent prediction model for limit support pressure

The instability of the shield tunnel's excavation face, particularly underwater tunnels, is one of the most hazardous factors in subsea tunnel excavation projects. Therefore, an accurate prediction of the limit support pressure to maintain the excavation face's stability is essential to minimize the possible risk of damage. This study proposed an intelligent prediction model to address these issues. First, the analytical formula of the limit support pressure of the excavation face was established through mechanical analysis to give the mechanics criterion for active instability of the excavation face. Subsequently, the numerical simulations were conducted to reveal the evolution mechanism of the excavation face instability. The result revealed that the buried depth of the tunnel, water depth, driving speed, internal friction angle, water content, cohesion, and support safety factor were the main factors affecting the limit support pressure. Furthermore, the support vector machine (SVM) model was established for predicting the limit support pressure. The prediction results agreed well with the actual data, thereby indicating the feasibility and convenient implementation of the SVM predictor. The proposed model was validated as an effective method for predicting the limit support pressure for further engineering applications.