ABSTRACT
Soil-bentonite-binder cut-off walls have gained popularity as an effective solution for controlling groundwater flow during deep excavation, especially in porous sandy soil. In two-phase cut-off wall construction, the incorporation of binder during the second phase can significantly influence the workability and cause bleeding. The use of reactive magnesia (MgO)-activated ground granulated blast-furnace (GGBS) has been shown to control excessive bleeding. However, the engineering properties of the hardened stabilized sand-bentonite mixtures, particularly in two-phase construction, have not been assessed. In this study, the permeability and strength of various sand-bentonite-binder mixtures were evaluated using flexible wall permeability and unconfined compressive strength (UCS) tests, respectively. The effectiveness of MgO-GGBS was compared with other binder types including ordinary Portland cement (OPC) and quicklime (CaO)-activated GGBS. The result showed that the UCS of MgO-GGBS stabilized soil was 2 to 4 times greater than that of OPC stabilized soil and comparable to that of CaO-GGBS stabilized soil. The hydraulic conductivity of all MgO-GGBS mixtures was well below the permeability requirement of 10-9 m/s for seepage cut-off wall, but OPC mixtures had much higher permeability that did not meet the requirement. The hydration products of MgO-GGBS mixture were identified as calcium silicate hydrate, hydrotalcite-like phases, and ettringite, which bonded the soil particles and contributed to the strength and impermeability of cut-off walls. This work highlights the potential application of an effective binder of MgO-GGBS in stabilizing sand-bentonite mixtures for two-phase seepage cut-off walls.
