The influence of freeze-thaw action and particle size characteristics on the shear resistance of black soil

Abstract

Abstract To explore how freeze-thaw action modulates the relationship between particle size and soil shear strength, cohesion ( c ), internal friction angle ( φ ), and shear strength ( τ ) of seven particle size groups (at 4% water content) were measured using a direct shear apparatus. Results show: Particle size significantly influences c dynamics. naturally graded soil and d ≥ 1 mm (particle size ≥ 1 mm) groups exhibit decreasing c with freeze-thaw cycles, while d < 1 mm groups show the opposite trend. Among them, d 5–10 mm groups are least affected, and d < 0.25 mm groups are most affected, with c stabilizing after 6–9 cycles. For φ , d ≥ 2 mm groups first increase then decrease, whereas d < 2 mm groups show the reverse. d < 0.25 mm groups retain the highest φ values; after 30 cycles, d 2 –5  mm groups exhibit the largest φ decrease (− 4.70%), while d 0.5−1  mm groups show a slight increase (2.17%). Naturally graded soil has the highest τ due to inter-particle synergistic effects, with d 1–2  mm groups leading among single particle size groups. τ correlates positively with cycles for d < 1 mm groups but negatively for naturally graded soil and d ≥ 1 mm groups. Particle size dominates shear resistance ( c :71.78%, φ :45.43%, τ :53.22%), with freeze-thaw cycles as a key secondary factor (18.82%, 11.27%, 20.52%).