Calculation of layered foundation reaction force and prediction of tunnel underpass settlement based on improved MSD

The author proposes a layered foundation reaction calculation method based on an improved MSD to address the complex settlement problem caused by tunnel underpass under layered foundation conditions. This method comprehensively considers longitudinal settlement, lateral deformation, energy conservation, and geometric coordination relationships, and establishes a settlement prediction framework that is more in line with reality through multi-layer weighted correction of the traditional MSD model. In the system parameter scanning and comparative analysis, it was found that the sensitivity of the ultimate bearing capacity Pk, initial foundation reaction coefficient Ko, and nonlinear shape parameter Rf to soil stiffness, strength, and geometric factors under layered foundation conditions were significantly higher than those of homogeneous foundation, exhibiting stronger nonlinear response characteristics; Meanwhile, the foundation reaction coefficient calculated by the passive displacement method is closer to the measured value under complex layered conditions, which verifies the effectiveness and applicability of the improved MSD method. In the engineering example, the predicted values of the layered MSD method are highly consistent with the monitoring curve, which is significantly better than the traditional method. The results indicate that the improved MSD method can effectively improve the accuracy and reliability of tunnel settlement prediction.