Nonlinear model for compressibility of partly saturated soils

Development of a comprehensive model for soil deformation remains an important research goal for soil scientists. Accounting for the effect of changing soil water content is a critical component of this goal, A nonlinear mathematical model for prediction of the bulk density as a function of soil water content and normal stress was developed and tested. The proposed model is an extension of a previously developed nonlinear model for soil compression obtained by including degree of soil saturation as the measure of soil water content, The model predicts bulk density at both low and high stresses and at soil water contents ranging from the permanent wilting point to saturation. The model was tested with data obtained from one-dimensional consolidation tests of undisturbed soil cores from the 7- to 12-cm depth of three Andisols characterized by amorphous clay minerals or volcanic ash and one fine-textured mineral soil containing a mixture of crystalline clay-sized minerals. The standard error of the regression of predicted vs. measured compressed bulk densities ranged from 0.029 to 0.040 Mg m(-3). Application of the model showed that the soil compressibility varied substantially between soils. The compressibility of Andisols was less sensitive to differences in soil water content than was the fine-textured soil that contained few amorphous clay minerals, The proposed model is a promising new method for predicting the compressibility bf soils for a wide range of stresses and soil water contents.