Pneumatic-vibratory probe compaction inducing horizontal stress increase in collapsible loess

This study focuses on the horizontal stress changes induced by pneumatic-vibratory probe compaction (PVPC) in collapsible loess, aiming to reveal the mechanism through which PVPC reinforces loess foundations. Field tests with compaction grid spacings of 1.2, 1.3, and 1.4 m demonstrated that the collapsibility of the soil layer within an 8 m depth range was completely eliminated. Cone resistance and sleeve resistance increased by more than 100% on average, indicating significant reinforcement. Horizontal stress changes caused by the vertical vibration of PVPC are primarily influenced by the sleeve resistance ratio, with minimal dependency on the friction angle. The horizontal stress ratio ( K 1 / K 0 ) increased markedly in the upper 0–4.0 m, ranging from 4.0 to 8.0, and stabilized in the 4.0–7.5 m range at values between 1.9 and 3.1. Microstructural analysis revealed that PVPC reorganizes soil particles, increasing density, reducing internal voids, enhancing inter-particle bonding, and redistributing stress within the soil. These changes collectively explain the significant elevation in horizontal stress, which improves the stability and load-bearing capacity of loess foundations.