Consolidation of ground with ideal sand drains based on Hansbo's flow

A deviation of the pore water flow from the Darcian law is observed at small hydraulic gradients according to laboratory and field investigations on some saturated cohesive soils, which can account for that there are aspects of consolidation behaviour of ground with vertical drain system that cannot sometimes be explained on the basis of these conventional consolidation theories using the Darcian flow. In order to improve the computational accuracy of consolidation of vertical drains, the Hansbo’s equation, described by the power function for lower seepage velocity and the linear function for higher seepage velocity, is introduced to describe the non-Darcian flow. Accordingly, the Barron’s consolidation theory for clayey ground with vertical ideal sand drains is modified under the assumption that the vertical strains develop freely, and the numerical analysis is performed using the finite difference method. Then the effects of the parameters of Hansbo’s flow and the ground thickness on the consolidation process of ground with vertical drains are investigated. The numerical results indicate that, compared with that of the Darcian flow, the behaviour of Hansbo's flow controls the dissipation of pore water pressure in clay ground, and thereby reduces the settlement rate of ground. In addition, the influence of radial drainage considering the Hansbo’s flow has more influence on the dissipation of pore water pressure than that considering the Darcian flow. If the Hansbo’s equation is simplified as the power function to describe the flow, the degree of consolidation of ground will be overestimated, especially in the preliminary stage of consolidation. Finally, the difference as regards the degree of consolidation obtained by assuming the equal strain theory or by assuming the free strain theory is investigated.