Abstract：This study investigates the behavior of in-situ weak expansive soil as a road subgrade foundation under coupled hydrological and mechanical actions. A series of drying-wetting cycle tests were conducted under varying overburden pressures and moisture variation amplitudes. The results reveal the coupled effects of load and moisture amplitude on the volumetric response of the foundation soil. Subsequently, isotropic consolidation and true triaxial shear tests were performed under constant water content using an unsaturated soil true triaxial apparatus to elucidate the regulatory mechanisms of load, drying-wetting history, and intermediate principal stress on the strength characteristics of the in-situ soil. The key findings are as follows: the coupled actions of load and moisture amplitude dictate the direction of cumulative deformation. Specimens exhibit cumulative expansion under zero load, with the magnitude increasing with larger moisture amplitudes. In contrast, specimens transition to cumulative contraction when a load is applied, and this contraction intensifies with higher load or moisture amplitude. The load alters the evolution pattern of swell-shrink magnitude and exerts a continuous suppressive effect on volumetric changes. The critical water content (wc) increases with higher load, moisture amplitude, and the number of cycles. The wc-N curves under different loads form hysteresis loops, indicating an irreversible path dependency of the swell-shrink characteristics on load history. The peak strength degrades with an increasing number of drying-wetting cycles but improves with higher load, intermediate principal stress, or smaller moisture amplitude. All three factors effectively decelerate the rate of strength deterioration. Strength stabilization occurs prior to deformation stabilization. Particularly under conditions of low load or small moisture amplitude cycles, the long-term cumulative deformation risk must be assessed independently. The research outcomes provide a theoretical basis for foundation treatment design and long-term performance prediction of subgrades in expansive soil regions.
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2026, Vol. 45 
