Coupled Effect of Cross-Sectional Shape and Load Reduction on High-Filled Cut-and-Cover Tunnels Considering Soil–Structure Interaction

High-filled cut-and-cover tunnels (HFCCTs) are common in northwestern China because their construction allows usable land over the CCT to be reclaimed. However, due to the unique landforms of the Loess Plateau in this region of China, the amount of backfill soil that is needed for HFCCTs is enormous, and the backfill must be high enough to maximize the usable land. Currently, the main challenges for the construction of HFCCTs are ultrahigh earth pressure and safety concerns related to the existing CCT lining structure. This paper discusses physical modeling tests that were conducted to investigate (1) load reduction methods that utilize expanded polystyrene (EPS) in the backfill soil; and (2) structural modifications to CCTs. The experimental results agree well with the numerical analysis results. The numerical analysis helped to determine suitable thicknesses of EPS material for load reduction when the CCT was subjected to different backfill heights. Also, by modifying the cross-sectional shape of the lining structure of CCT, the internal forces could be altered to make the concrete structure support more compressive loads rather than succumb to bending moments. This study found that the coupled effects of load reduction using EPS and cross-sectional modifications of the CCT lining structure can significantly reduce the required thickness of the CCT lining structure, enhance the safety of the CCT, and increase the allowable backfill height.