Pore Characteristics and Water Permeability of Self-Compacting Soil–Cement Mixtures Used in the Deep Soil Mixing Method

The deep soil mixing (DSM) technique is employed to create cut-off walls within flood protection levees by mechanically mixing in situ soil with hydraulic binders (cement and/or lime). Because there have been few studies of this innovative technique, a detailed investigation into the microstructural characteristics and theoretical water permeability of self-compacting soil–cement mixtures was conducted. The effects of key parameters, such as water content, clay mineral type and quantity, cement content, and curing time and temperature, were explored systematically. Coupling mercury intrusion porosimetry (MIP) and water porosity for total porosity and pore-size distribution measurements, the results indicated that higher cement content promoted the formation of cementitious hydrates (i.e., CSH, CASH, and so forth), enhancing nanoporosity while reducing the volume of larger micropores. Conversely, higher W / C ratios increased the total porosity and altered the size distribution of nanopores and capillary pores, which mainly govern the material hydraulic behavior. The clay mineralogy, characterized through various specific surface areas, water adsorption quantities, particle size or flexibility, and dispersion properties of particle aggregates also impacted pore-size distribution. Specifically, illitic mixtures had reduced micropores with increasing cement content, whereas kaolinitic mixtures with large clay particles under rigid platelets form maintained stable micropore structures. A strong correlation between calculated water permeability ( K ) and the threshold pore diameter ( D c ) was established using the extended Ait-Mokhtar model, confirming that better knowledge of the pore-size distribution helps significantly to forecast the hydraulic performance of DSM material and its long-term durability.