Field test of lime soil compaction pile improving collapsible loess foundation

The formation of collapse holes can adversely affect the efficacy of the lime soil compaction piles. This study employs a combination of field experiments, laboratory tests, microstructure observations, and theoretical analyses to elucidate the mechanisms underlying the improvement of soil compaction pile composite foundations in the Gansu region, particularly in the context of collapse hole problems. The conclusions are showed as following: (1) The implementation of lime soil compaction piles results in a gradual reduction of the void ratio of the loess between the piles due to horizontal extrusion effects. As the number of ramming times increases, the state of the pile transitions from loose to dense. This transformation is further enhanced by bridging and cementation within the pile body, leading to an enlarged particle structure and a reduction in pore size. (2) An increase in the number of ramming times correlates with a rise in both the average dry density and penetration resistance of the lime soil compaction piles. However, the presence of collapse holes can lead to the mixing of collapsed loess and lime soil filler, which significantly diminishes the penetration resistance of the pile body in the sections affected by collapse. Notably, after 16 ramming times, there is a marked increase in the dry density of the collapsed hole sections. (3) The issue of collapse holes contributes to an increase in the falling height of the rammer hammer, which in turn reduces the compressive stress within the hole and diminishes the extrusion of loess between the piles. Furthermore, the collapse effect negatively impacts the effectiveness of collapsibility elimination in the loess between the piles. This paper provide theoretical value and practical guidance for the enhancement of collapsible loess foundations.