Delayed Drainage of a Largely Deformed Aquitard due to Abrupt Water Head Decline in Adjacent Aquifer

Abstract

A governing equation of drawdown was put forward to describe the one-dimensional large-strain consolidation behavior of an aquitard without consideration of the creeping effect. An analytical solution was derived to characterize the drawdown variation in the aquitard subjected to sudden hydraulic head decline in adjacent confined aquifer. The characteristics of the groundwater dynamics and water balance in the aquitard have been analyzed based on the analytical solution. A comparison analysis of results has been made between the large-strain theory and the classical small-strain theory. The type-curve fitting method was used to determine the hydrogeological parameters, on the basis of the observed variations of aquitard deformation with time. The analytical solution was thus validated by a comparison with the observed experimental results. It is found that the water drainage of aquitard is obviously delayed in response to the water head decline in the adjacent aquifer. All delayed water release from the aquitard terminates when the consolidation time reaches the value of l2/cv0. The aquitard deformation predicted by the large-strain theory is less than that given by the small-strain theory, and the prediction discrepancy of these two theories increases with the increasing soil compressibility.