Preloaded-cement-soil filled steel tubular columns: Concept and axial compression performance

Weathered residual soil of granite (WRSG) is the predominant type of excavated soil in southern China. This study explores the high-quality utilisation potential of WRSG by mixing it with a small amount of cement and preloading it within steel tubes to create preloaded-cement-soil filled steel tubular (PCSFST) columns. The research investigates the relaxation behaviour and axial compression performance of PCSFST columns through experiments, focusing on the influence of preloading indicator, cement content ratio, and water-to-solid rat io on their axial compression behaviour. The experimental results showed that an increase in the preloading indicator significantly enhanced the axial bearing capacity of the PCSFST column. Specifically, when the preloading indicator increased from 30 % to 90 %, the axial bearing capacity increased by 22.7 %. Although the increase from 6 % to 12 % in the cement content ratio significantly improved the unconfined compressive strength (UCS) of the cement-soil core, the corresponding reduction in the confining effect only resulted in a 3.2 % increase in the axial bearing capacity, indicating a limited benefit. A moderate increase in the water-to-solid ratio significantly boosted the UCS of the cement-soil core, which in turn, enhanced the axial bearing capacity of the PCSFST column. After the preloading load was released, the cement-soil core exhibited longitudinal rebound deformation, which significantly reduced the confining effect provided by the steel tube. Nevertheless, the contribution of the confining effect to the axial bearing capacity can reach as high as 37 %, partially compensating for the relatively low UCS of the cement-soil core. Finally, based on the experimental results, a formula was proposed to predict the axial bearing capacity of PCSFST columns, which demonstrated high prediction accuracy.