Double Drainage Consolidation Theory of Vertical Drains Based on Continuous Drainage Boundary Conditions

Conventionally, drainage boundaries are often assumed to be either perfectly permeable or completely impermeable. However, a more realistic approach considers continuous drainage boundaries. In this context, an analytical solution for double drainage consolidation in vertical drains is derived. The proposed method is evaluated against existing solutions and finite element simulations. The study investigates the impact of drainage capacity, soil nonlinearity, smear effect, and well resistance. The results show that the continuous drainage boundary parameters (i.e., b and c) significantly affect the distribution of excess pore water pressure and the consolidation rate. Increasing b and c allows realistic modeling of drainage capacity variations from impermeable to permeable boundaries. Notably, when b not equal c, the maximum excess pore water pressure plane shifts from the mid-height of the foundation soil, diverging from conventional consolidation theory. Soil nonlinearity (Cc/Ck) and boundary permeability (b and c) jointly affect consolidation. Higher Cc/Ck values correlate with more detrimental consolidation effects. Minimizing disturbance around vertical drains during construction is crucial due to well resistance and smear zone effects, which can significantly slow down consolidation. This study provides an analytical solution considering soil nonlinearity for predicting consolidation in actual engineering scenarios involving vertical drainage trenches.