Abstract
Soilbags represent an emerging three-dimensional geosynthetic reinforcement technique, valued in permanent civil engineering for their structural strength, site adaptability, and economic efficiency. Despite growing application, the fundamental mechanisms of enhancing the deformation modulus of reinforced soil have not been fully elucidated. This study advances the understanding by integrating field, theoretical, and experimental approaches to unravel the modulus‑enhancement mechanisms. Field plate load tests on single‑layer soilbag‑reinforced foundation based on soil‑rock mixtures recorded an average increase in deformation modulus of approximately 23.4% compared to unreinforced soil-rock mixtures, confirming the technique's practical performance. A unified stress-strain framework is developed, which explicitly incorporates the additional confinement stress generated by geotextile tension and traces the resulting transition in stress paths of the encapsulated soil, thereby offering a mechanistic interpretation of modulus improvement. The framework is validated through unconfined compression tests on both clay‑ filled and sand‑filled soilbags, which further clarify how tensile confinement actively redistributes internal stress paths. The results reveal that the enhanced modulus arises from the coupled interaction between compressive hardening of the infilled soil and tensile confinement provided by the geotextile bag, offering a mechanistic basis for optimized design and application of soilbag reinforcement.