Sustainable deep soil mixing using GGBS–dolomite based geopolymer for soft ground improvement

Department of Civil Engineering, Indian Institute of Technology, BHU, Varanasi, India.

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Abstract

The deep soil mixing (DSM) technique has been extensively adopted worldwide for soft ground improvement due to its effectiveness in reducing settlement, enhancing the stability of embankments over soft soils, and improving earthquake resilience. However, the conventional use of ordinary Portland cement (OPC) as a binder contributes substantially to carbon emissions. To address this environmental concern, this study investigates the potential of a sustainable industrial waste-based geopolymer binder composed of ground granulated blast furnace slag (GGBS) and dolomite, activated with sodium hydroxide (NaOH) and liquid sodium silicate (Na2SiO3), as a replacement for OPC in DSM columns, by conducting unconfined compressive strength analyses. Moreover, a series of laboratory model tests was conducted on embankments supported by groups of end-bearing geopolymer-stabilized soil columns (GPSCs) installed in very soft clay to simulate traffic loading. The test results were further validated through finite element analyses using PLAXIS 3D. The optimum mix, corresponding to a NaOH concentration of 8 M, NaOH: Na₂SiO₃ ratio of 25:75, liquid-to-precursor ratio of 1, and GGBS-to-dolomite (S:D) ratio of 16:4 (precursor/kaolin clay = 20%), achieved an unconfined compressive strength (UCS) of 1.47 MPa. The geopolymer-treated soft soil with an S:D ratio of 16:4 exhibited 26.30%, 32.59%, and 38.35% higher strength than the OPC20 specimens at 7, 14, and 28 days of curing, respectively. It was also found that the incorporation of end-bearing GPSCs in soft soil beds improved the stiffness and ultimate bearing capacity of the composite soft ground by 246.92% to 418.8% for area replacement ratios of 12.7%, 17%, and 21.2%. The finite element outcomes showed trends similar to the laboratory observations, validating the effectiveness of geopolymer-based DSM columns as a sustainable and high-performance solution for soft soil improvement.