Static and dynamic characteristics of alkali residue-based lightweight soil subgrade filler subjected to freeze–thaw cycles

Abstract

Alkali residue-based lightweight soil (A-LS) is a low-carbon, high-strength subgrade material synthesized from alkali residue, ground granulated blast furnace slag, cement, and a foaming agent. This study employs static and dynamic triaxial tests to elucidate the effects of freeze–thaw (F–T) cycling on the mechanical performance of A-LS. After 10 F–T cycles, A-LS showed no macroscopic cracking or spalling, though surface porosity rose from 51.46 % to 54.78 % and pore walls became roughened. Mass variation exhibited cyclic fluctuations with an overall decline, and volumetric strain remained below 0.25 %. Deviatoric stress–strain curves retained distinct elastic, plastic yield, and strain-softening stages, yet F–T cycling induced internal microcracks that reduced both peak and residual strengths, the latter experiencing greater degradation. Backbone curves maintained a hyperbolic form but shifted toward higher strains post-cycling, indicating diminished stiffness. The dynamic elastic modulus (E_d) increased initially due to pore compaction, then declined nonlinearly as microcracks developed. E_dmax decreased linearly by 15.9 %–19.5 % after 10 cycles, and a predictive model (R² = 0.996) accurately captures E_dmax degradation as a function of confining pressure and F–T damage. Damping ratio (D) decreased to a minimum at a transitional strain of 0.02 %–0.04 % before rising to a plateau. Moreover, the transitional strain increased from 0.028 % to 0.043 % with higher confining pressures but was insensitive to the number of F–T cycles. These findings provide a theoretical basis for the subgrade applications of A-LS in seasonal frost regions.