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 $\left(\rho \right)$ ranging from $1.056–1.450\mathrm{Mg}∕{\mathrm{m}}^3$ , and effective consolidation stresses $\left({\sigma }_{\mathrm{vc}}^{\prime }\right)$ ranging from $11–135\mathrm{kPa}$ . The secant shear modulus $\left(G\right)$ and equivalent damping ratio $\left(\xi \right)$ were modeled as variables dependent on the shear strain amplitude $\left({\gamma }_c\right)$ , consolidation stress $\left({\sigma }_{\mathrm{vc}}^{\prime }\right)$ , and OC. The residuals of the regression models were analyzed against other predictor variables including undisturbed density $\left(\rho \right)$ , loading frequency $\left(f\right)$ , and number of loading cycles $\left(N\right)$ . A regression model for $\rho$ was developed, and conditional probabilities were used to improve the estimation of $G$ and $\xi$ when $\rho$ measurements were available. The database of in situ measurements of shear wave velocity $\left(V_s\right)$ was used to adjust the regression model for in situ conditions. Variances and correlations in the regression models are presented.