Comparative Performance of Geosynthetic-Encased Columns with Steel Slag and Gravel for Soft Soil Improvement

Steel slag is an environmentally friendly material with significant potential as an alternative to gravel for encased columns in soft ground improvement. However, the performance of composite foundations improved by geosynthetic-encased steel slag columns (GESSC) remains somewhat unclear. This study compares the working performances of GESSC and geosynthetic-encased stone column (GESC) composite foundations, as well as untreated foundations, through a series of large-scale experiments. Additionally, cone penetration tests were conducted on both the untreated and GESSC foundations to assess changes in soil strength before and after loading. The results show that both GESSC and GESC significantly increase the bearing capacity of soft clay, demonstrating an approximate 10-fold increase compared to the untreated foundation. The GESSC composite foundation marginally outperforms the GESC in bearing capacity during the elastoplastic stage. Furthermore, upon reaching the ultimate bearing capacity, the GESSC exhibits greater radial strain and less settlement than the GESC, owing to the unique redistribution of steel slag and gravel. Both types of foundations effectively transmit vertical pressure to deeper soil layers, with GESSC demonstrating superior load transmission capabilities and a more uniform distribution of soil stress along the depth. The excess pore-water pressure and its accumulation rate within the GESSC foundation are typically lower than those in the GESC composite foundations, underscoring the superior drainage capabilities of GESSC. This enhanced drainage capacity leads to a higher consolidation ratio within the soil, resulting in a significant improvement in soil strength after loading compared to the untreated foundation.