Groutability evaluation of permeation grouting in saturated sands through two-dimensional scaled physical modeling

This study explores the characteristics of permeation grouting and induced ground deformation in various fully saturated sands using a two-dimensional scaled physical model with bentonite-cement grout. A bentonite-cement grout was injected into Hele-Shaw-type soil models under varying soil types, injection rates, water-cement ratios, and vertical effective stresses, while soil displacement was monitored using particle image velocimetry. Results show that groutability was strongly influenced by the particle size of host soils. In coarse sands, grouting remained stable, and deformation was mitigated by increasing the water-cement ratio and effective stress. In fine and silty sands, conversely, higher injection rates triggered unstable grouting with fracture generation, leading to irregular ground heaving, and the fracture-induced deformation was also significant even at a higher water-cement ratio and effective stress. Particle-level dimensionless analysis considering the shear-thinning characteristics of the bentonite-cement grout reveals that the grout seepage pressure can serve as an indicator of the grouting pattern: stable versus unstable grouting. This study proposes new groutability criteria incorporating both the grain size ratio between grout and host soil and viscous pressure normalized by effective confining stress. These findings are expected to improve grouting design strategies through experimental observations and particle-scale mechanics.