Lattice-shaped ground improvement by mixing soil and alkali-activated slag for liquefaction mitigation

Alkali-activated slag (AAS), an environmentally friendly material, has recently attracted increasing attention for applications in soil improvement. However, most of the studies focused on the geomechanical behavior of non-liquefiable soils strengthened with AAS. The objectives of this study are to examine whether AAS is effective for strengthening liquefiable soil and to evaluate the effectiveness of AAS in deep soil mixing (DSM) technology for mitigation of liquefaction. The mechanical properties and microscale mechanism of the improvement of liquefiable soil by AAS under standard curing, water curing, and seawater curing conditions are studied first. Then, the strengthening effect of the DSM technique using the soil-AAS mixture on the soil-pile-superstructure system is studied by three-dimensional numerical analyses. The results show that the compressive strength of the soil-AAS mixture is much greater than that of the soil-cement mixture. Compressive strength of 32 MPa was obtained for a soil-ASS mixture with 25% slag content under 28-day standard curing. Moreover, the DSM technique using the soil-AAS mixture is an effective method for liquefaction mitigation; the maximum lateral displacement of the pile during shaking can be reduced by half when the area improvement ratio is 20 %.