The excessive load from the high embankments of high-filled cut-and-cover tunnels (HFCCTs) threatens the safety and stability of HFCCTs. Relatively low-compacted (RLC) soil can reduce such loads in the short term, but the long-term ability of RLC soil to reduce the load on HFCCTs is unknown. The changes in the soil arching effect that are resulted from soil creep needs to be considered carefully in HFCCT design. Three stages of analysis were conducted in this study: immediately after backfilling (0 month), during backfill creep, and after the soil deformation has stabilized (240 months/20 years). A finite difference program, FLAC3D, was employed to investigate the soil’s vertical earth pressure and displacement distribution around a cut-and-cover tunnel (CCT). The Burgers model was used to simulate the creep behavior of the soil. In addition, parametric studies for different dimensions and locations of RLC soil were conducted. The results show that the soil arching effect that is due to the inclusion of RLC soil works well initially to reduce the load but eventually disappears, which can result in a significant load rebound greater than 100 kPa and jeopardize the stability of the HFCCT.

The newly constructed Luofengshan Tunnel obliquely underpasses the operating Hanyicun railway tunnel, requiring an integrated assessment of deformation response and service safety. This study combined field monitoring, ultrasonic shear-wave reflection imaging, and three-dimensional numerical simulation to evaluate track-bed settlement, lining deformation, floor integrity, lining stress, and structural safety. The complete third-party monitoring record showed that vertical deformation dominated the tunnel response. The final maximum cumulative values were −17.44 mm for manual lining settlement, −14.91 mm for automated lining settlement, and −11.30 mm for track-bed settlement; the corresponding maximum absolute values of horizontal displacement and convergence were 1.82 mm and 1.40 mm, respectively. Same-period comparisons showed that deformation increments decreased after breakthrough, and post-lining flood-season monitoring showed monthly rates below 1 mm/month. Ultrasonic imaging detected no evident voids or collapse within 2.0–2.2 m below the floor. Numerical simulation showed that incorporating measured initial deformation increased the maximum compressive stress from 4.95 MPa to 6.26 MPa, whereas subsequent underpass excavation and train loading increased it slightly to 6.28 MPa and 6.33 MPa, respectively. The final minimum safety factor was 3.18, indicating that the underpass impact remained controllable.