Numerical Evaluation of a Mirror-Slope Rockfill Replacement for Embankments in Warm Island Permafrost

Highway embankments in warm island permafrost regions of Northeast China are vulnerable to climate warming and foundation softening. To improve long-term temperature and deformation control, a mirror-slope rockfill layer (MSRL) and corresponding mirror-slope rockfill embankment (MSRE) are proposed by mirroring the embankment side-slope geometry. A two-dimensional hydro–thermal–mechanical model was established for the K49 section of S201 Highway, and 40-year simulations were conducted at a warming rate of 0.06 °C/a for an unprotected embankment, a rectangular rockfill embankment, and four replacement-interface slopes. In Year 40, centerline settlement decreased from 29.20 cm in the unprotected embankment to 0.86 cm in the MSRE. Relative to the rectangular scheme, absolute vertical and horizontal displacements at the right slope toe decreased by 2.10 and 2.90 cm, respectively. Among vertical, 1:1.5, 1:2.5, and 1:3.5 interfaces, the 1:2.5 MSRL reduced maximum shear stress and rockfill consumption by 30.1% and 16.4%, respectively, relative to the vertical interface. Further flattening to 1:3.5 provided limited mechanical improvement but increased slope-toe temperature fluctuations. The 1:2.5 MSRL therefore offers a feasible balance among thermal control, deformation control, and material consumption under the investigated conditions.