Numerical Analysis of Protective Performance of Segmented Excavation Schemes for Metro Tunnels Considering Excavation-Induced Disturbance

Abstract

This paper presents an integrated laboratory and numerical study on the effects of excavation-induced soil disturbance on the displacement of underlying metro tunnels, as well as the protective performance of different segmented excavation methods. Artificial disturbed soils were prepared by mixing salt grains and different cement contents into remolded Ningbo silty clay. One-dimensional compression tests and triaxial shear tests were then conducted. These tests were used to investigate and compare the engineering properties of undisturbed and artificially disturbed soils. Subsequently, the Hardening Soil Model with Small Strain (HSS) parameters were obtained for soils under varying degrees of disturbance. Considering the deterioration of soil properties due to disturbance and based on the disturbance zoning determined from the unloading influence depth and field measurements, numerical simulations were performed using Plaxis 3D. These simulations analyzed tunnel displacements induced by large-area direct excavation and three segmented excavation schemes. The results indicate that excavation-induced disturbance can significantly increase tunnel vertical displacement. Compared to unmitigated direct excavation, segmented excavation methods (i.e., block jumping excavation, ends to center excavation, and sequential excavation) can reduce the average tunnel displacement by about 28%. Among the three schemes, block jumping excavation offers the best balance between deformation control and efficiency with the highest comprehensive benefit index (11.04%). Ends to center excavation provides optimal deformation control but exhibits relatively low efficiency. In contrast, although sequential excavation effectively reduces displacement, it leads to concentrated deformation and low construction efficiency, making it the least favorable option.OPEN ACCESS Received: 13/04/2025 Accepted: 30/07/2025 Published: 22/09/2025

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