Deep Soil Mix (DSM) columns are a widely adopted ground improvement method for soft, cohesive soils (alluvial, estuarine, and marine clay). Accurate design for seismic and vibrational loading requires reliable estimation of dynamic properties: shear modulus (G), damping ratio (D), and strain thresholds. However, current studies of G and D for the treated and untreated soil were conducted separately, neglecting the critical composite effect of treated soil columns within an untreated soil matrix. Furthermore, existing dynamic regression models, primarily based on Resonant Column Test results (RCT), are limited to γ=0.1%, omitting the highly non-linear behaviour at larger strains (γ > 1%) commonly encountered during seismic events. This research addresses this gap by using cyclic triaxial tests (CT) to study dynamic properties beyond 0.1% shear strain. The study investigates the complex influence of soil moisture content (w) / void ratio (e) in conjunction with plasticity index (PI) and effective pressure (σ’) on soil dynamic property behaviour. First, an improved basic equation model is developed for untreated soil based on PI, σ’, and w factors. This model is then seamlessly extended to cement-treated soil, incorporating cement content (CC) and moisture content (MC) to provide a unified framework that accounts for the parent soil type. In contrast, current cement-treated soil models are developed separately from untreated soil models and require complex dimensionless stress ratios. Crucially, a final composite model is developed to predict the combined effect of cement-treated soil columns in an untreated soil matrix from tests on representative cement-soil cores in untreated soil. The model, expressed in terms of the cross-sectional area replaced (AR) of untreated soil by treated cement soil, effectively simulates the non-homogeneous, anisotropic nature of the composite soil mass characteristic of DSM column-type ground improvement. The unified models provide essential representative values for shear modulus, strain thresholds, and damping ratio to estimate the response of DSM columns under dynamic loads in seismic or cyclic loading conditions.
John Wong Kok Hee (Sat,) studied this question.