Subgrade uplift mechanisms of high-speed railways in red-bed regions: insights from field monitoring and numerical modeling

Persistent subgrade uplift is an emerging geohazard for high-speed railways in red-bed regions, but the roles of basal lithology and stress redistribution remain poorly constrained. We investigated two uplift-affected deep-cutting sections at Neijiang North Station on the Chengdu-Chongqing Passenger Dedicated Line using borehole lithological profiles, layered deformation monitoring, in situ lateral pressure measurements, and numerical modeling. Section I is dominated by mudstone within the upper 12 m below the cutting base, whereas Section II contains more frequent sandstone-mudstone interbeds. Section I consequently shows greater annual uplift displacement and a higher uplift rate, indicating that mudstone-rich basal strata are more susceptible to long-term uplift. Layered monitoring shows that uplift generally increases toward the ground surface, whereas sandstone-bearing intervals locally reduce deformation. At the representative K152 + 790 cross-section, the numerical model also indicates localized horizontal stress concentration near a sandstone interbed. The conventional CVISC model reproduces the long-term creep trend but not the observed seasonal acceleration. In contrast, the swelling-creep model better reproduces the monitored temporal pattern, and its simulated lateral pressure coefficients are broadly consistent with borehole measurements. Together, the field and numerical results indicate that uplift in red-bed deep cuttings reflects excavation-induced stress redistribution, swelling-creep deformation of mudstone, and mechanical heterogeneity associated with sandstone-mudstone interbedding. These findings provide a basis for identifying uplift-prone cuttings and targeting deformation-control measures in red-bed railway corridors.