Consolidation Characteristics of Phosphatic Clays

Abstract

Reliable and convenient testing technique and analysis are used to evaluate the void ratio-effective stress and void ratio-permeability relations for several types of very soft phosphatic waste clays. The technique is based on the seepage-induced consolidation test in which a soft soil sample is subjected to a constant downward flow rate and its final consolidated height and bottom effective stress are measured as the sample reaches steady state conditions. These two data points and the measured zero effective stress void ratio represent three reliable experimental data in the low range of effective stress, where the consolidation constitutive relations are highly nonlinear. In the higher effective stress range, the loading and permeability tests are used to determine the coefficient of permeability and effective stress corresponding to a given void ratio. An efficient algorithm to describe the steady-state flow in soft soils and a parameter-estimation scheme are employed for the determination of the soil consolidation parameters needed in the finite strain consolidation theory. The laboratory data of the restricted flow test and the transient seepage-induced consolidation test and the field measurements in three phosphatic clay settling ponds confirm the results obtained from the seepage-induced consolidation testing and analysis.