Approximation of the Time Rate of Consolidation for Hydraulically Placed Fine Coal Refuse Using a Variable Coefficient of Consolidation Method

Terzaghi’s consolidation theory assumes strain in soil due to applied overburden pressure is small, and permeability and thus the coefficient of consolidation (C_v) remain constant during consolidation. Although valid for soft soil consolidation, the C_v for hydraulically placed slurry materials with low solids content may change significantly during the consolidation process as the material transitions from a slurry to a solid. In this study, a spatial and temporal variable C_v was used to predict the time rate of consolidation of fine coal refuse placed in an impoundment as a slurry. The results suggest the variable C_v method may best reflect the low degree of consolidation at shorter times when the material is still essentially slurry. At longer times, a similar degree of consolidation can be obtained with a constant C_v value obtained from consolidation measurements at low stress levels. The consolidation response of hydraulically placed slurry at shorter times is important for construction staging and personnel safety, but the constant C_v approach may be useful for estimating the time for greater degrees of consolidation.