Small to large strain mechanical behaviour of an alluvium stabilised with low carbon secondary minerals

Abstract

Deep dry soil mixing is a popular ground improvement technique used to strengthen soft compressible soils, with Portland cement being the most popular binder. However, its continued use is becoming less sustainable given the high CO2 emissions associated with its manufacture. Alkali-activated cements are considered to be viable low carbon alternative binders, which use industrial waste products such as blast furnace slag. This study focusses on the stabilisation of a potentially liquefiable soft alluvial soil using a dry granulated binder comprising sodium hydroxide-activated blast furnace slag (GGBS-NaOH). This binder has previously been demonstrated by the authors to have potential as a replacement for Portland cement due to its excellent engineering performance, positive contributions towards the circular economy, reducing energy usage and CO2 emissions in the construction sector. A detailed comparison in mechanical behaviour is presented between the soil in its reconstituted, undisturbed and cemented states after 28 days curing through the use of advanced monotonic triaxial testing techniques, including small strain measurements. Mechanical behaviour was specifically analysed regarding peak deviatoric strength, pore pressure response, stress – volumetric dilatancy, shear stiffness degradation over small to large strain ranges, critical state and failure surfaces. Using 7.5% GGBS-NaOH increased the stiffness and shear strength of the soil significantly, whereby the shear strains at which initial shear stiffness degrades is three times higher than the untreated undisturbed soil. As a result, larger amounts of dilation was observed during shearing of the material and resulted in an upward shift of the soil’s original critical state line due to the creation of an artificially cemented soil matrix through the precipitation of C-(N)-A-S-H gels.