Study on mechanical response of subgrade soil based on composite micro-expansive piles material

Xinyu Yao, Guangcheng Zhang, Yu Liu, Hongliu Rong, Fujia Meng

Introduction To enhance the inherent shear resistance of in-service highway subgrade soils and effectively improve subgrade safety resilience under short-term traffic closure conditions, this study proposes a technical scheme of installing actively-compacted micro-expansive piles. Methods Utilizing field-measured parameters of the subgrade soils and micro-expansive piles materials, a finite element model was established to analyze the effects of radial stresses (10 kPa, 50 kPa, 100 kPa) induced by various expansion rates on the stress distribution of the subgrade, as well as the influence of different diameter-to-spacing ratios (0.2, 0.4, 0.6) on the overall shear resistance of the subgrade. Results The results indicate that when the diameter-to-spacing ratio is 0.2, the radial stress attenuates by 89.53%–95.82% at the midpoint between two piles, indicating a limited effective stress transmission distance. Increasing the diameter-to-spacing ratio to 0.6 reduces the attenuation to 24.05%–25.15%, resulting in a more uniform stress distribution. Under a diameter-to-spacing ratio of 0.6 and a radial stress of 100 kPa, the maximum principal stress at the limit equilibrium state of the subgrade soils within the pile-influenced depth (0–5 m) is enhanced by an average of 60.5%. Discussion This study demonstrates that appropriately configured radial stress and diameter-to-spacing ratios can significantly enhance the subgrade’s resistance to shear failure, providing a scientifically effective approach for improving the safety resilience of in-service highway subgrades.