Carbonation technology using MgO and CO2 has been considered a rapid, effective, and environmentally friendly method for improving weak soils, mainly applied in shallow foundation treatments. This study introduced a novel MgO-carbonated composite pile (MCP) technique developed by injecting CO2 through a gas-permeable pipe pile into a MgO-mixing column for carbonation and solidification and its applications in weak subgrade treatments. Several field tests were carried out to study the characteristics of MCP as well as the performance of the MCP-reinforced foundations, including carbonation reaction temperature monitoring, pore-water pressure monitoring, standard penetration tests (SPTs), unconfined compressive strength (UCS) tests, static load tests, and subgrade deformation monitoring. Results showed vigorous and uniform carbonation within the MgO-mixing column, confirming the feasibility of constructing large-diameter MgO-mixing columns. The distribution, evolution, and affected zone of excess pore-water pressure induced by MCP installation were determined. The MCP exhibited good pile quality, with average SPT blow count and UCS value of 39 and 1021 kPa, respectively. MCP's bearing capacity was superior to prestressed high-strength concrete pipe piles, with ultimate vertical and lateral bearing capacities of 1920 and 119 kN, respectively. The MCP-reinforced foundation exhibited a small settlement of 54.5 mm under embankment loads. Life cycle assessment indicated significant carbon reduction benefits for MCP, with 44.7% lower carbon emissions compared to traditional composite piles.

This paper presents a numerical study to investigate the load transfer mechanism of a geosynthetic encased stone column (GESC) under embankment loading. The soils were modeled with a nonlinear elasto-plastic constitutive model incorporating a hyperbolic stress-strain relationship and the Mohr-Coulomb failure criterion. The geosynthetic encasement was modeled using a linearly elastic embedded liner element. Two interfaces were used to simulate the interaction between the geosynthetic encasement and the soils on either side. The validation of the numerical model was conducted using test data from vertical loading tests of the individual GESC installed in loose sand, including applied vertical stress-settlement curves and the circumferential strains profiles. Then, the influences of different design parameters on the load transfer mechanism of the GESC unit cell were investigated through a parametric study. Results indicate that the development of stress concentration ratio depends on the mobilization of tensile strains. The circumferential strains are significantly larger than the longitudinal strains, indicating that the circumferential tensile effect is dominant under embankment loading. The load transfer effect was gradually enhanced with increasing tensile strains. Increasing the geosynthetic encasement stiffness can be considered as an alternative to increasing the column infill friction angle in improving the load transfer effect.