Regression models for dynamic properties of highly organic soils

Regression models are presented for the dynamic properties of highly organic soils. The models are based on a database of triaxial and resonant-column/torsional-shear cyclic loading tests on thin walled tube samples mainly retrieved from the Sacramento-San Joaquin Delta. The soils in this database range from highly fibrous peat to amorphous organic clays with organic contents (OC) ranging from 14-81%, water contents ranging from 88-495%, total densities (ρ) ranging from 1.056-1.450 Mg/m³, and effective consolidation stresses (σ′_vc) ranging from 11-135kPa. The secant shear modulus (G) and equivalent damping ratio (ξ) were modeled as variables dependent on the shear strain amplitude (γ_c), consolidation stress (σ′_vc), and OC. The residuals of the regression models were analyzed against other predictor variables including undisturbed density (ρ), loading frequency (f), and number of loading cycles (N). A regression model for ρ was developed, and conditional probabilities were used to improve the estimation of G and ξ when ρ measurements were available. The database of in situ measurements of shear wave velocity (V_s) was used to adjust the regression model for in situ conditions. Variances and correlations in the regression models are presented.