Optimization of the single-side drift method for shallow-buried tunnels under large eccentric pressure based on the BiDoseResp settlement model

Taking a twin-tunnel project in Qinghai Province as a case study, this research investigates the excessive vault settlement of 14.8 cm observed at the right portal section. A three-dimensional finite element model was established to simulate the complete construction process using the single-side drift method. The results indicate that the "removal of the middle partition wall" acts as the critical factor triggering abrupt settlement. Innovatively, the BiDoseResp dual-dose response function was introduced, achieving high-precision fitting of the entire settlement-time history (R² = 0.9957). Using the validated model, two excavation sequences-shallow-buried side first versus deep-buried side first-were compared. Excavating from the deep-buried side first (Scheme B) reduced vault settlement on the shallow-buried side by 18.4%-20.5% and decreased the maximum axial forces in the support structure by up to 55.9%. Based on these findings, a risk control strategy was proposed for the left portal section, which prioritizes excavation from the deep-buried side, minimizes the exposure time of the middle partition wall, and incorporates dynamic settlement prediction via the BiDoseResp model. The outcomes offer theoretical insights and technical solutions for informatized construction and deformation early-warning in shallow-buried tunnels subjected to large bias pressures.