Behavior of GGBFS-Modified DSM Columns in Clay Soil: Strength–Permeability Characteristics and Predictive Laboratory Modeling

Abstract

This study investigated the influence of partially substituting cement with ground granulated blast furnace slag (GGBFS) on the unconfined compressive strength (UCS), splitting tensile strength (STS), and permeability coefficient (kDSM) of deep soil mixing (DSM) columns formed in clay soil. The water/binder ratio was kept constant at 1.0. Cast specimens were prepared using two binder contents, aw = 15% and 20% by dry soil mass, and five GGBFS substitution ratios of 0%, 10%, 20%, 35%, and 50%. Strength specimens were tested after 7, 28, and 56 days of curing, whereas permea- bility specimens were tested after 28 and 56 days. Four laboratory-scale DSM col- umns with a diameter of 300 mm and a length of 600 mm were formed for selected mixtures with aw = 20% and GGBFS ratios of 0%, 20%, 35%, and 50%; core samples were extracted after 28 days. UCS values ranged from 859 to 4939 kPa, STS from 182 to 830 kPa, and kDSM from 0.16×10⁻¹⁰ to 9.17×10⁻¹⁰ cm/s for cast specimens. GGBFS reduced early-age strength at 7 days, but improved strength and reduced permeabil- ity at later curing ages. The UCS and STS values of core samples were 45.26–69.79% and 63.00–77.58% of the corresponding cast specimen values, respectively, while permeability values of core samples were higher. SEM and XRD observations sup- ported the formation of hydration and pozzolanic products.