Positioning design of horizontal drain in sandwiched clay-drain systems for land reclamation

In practice, horizontal drains are often arranged at certain depth in dredged clays to accelerate the consolidation process in layered clay-sand reclamation subjected to surcharge preloading, and the layout of horizontal drain is usually determined based on a trial-and-error procedure. Based on the transfer matrix approach, a semi-analytical solution is derived using Laplace transform and its numerical inverse methods for use to optimize the design of horizontal drain in layered clay-sand reclamation. The effectiveness of the proposed technique is demonstrated by comparing against other analytical solutions. The sensitivity of the optimal position of horizontal drain to the anisotropic coefficient of consolidation, the thickness ratio, and the anisotropic permeability is discussed. Results show that the optimal position of horizontal drain is related to the drainage capacity in adjacent soil layers, and it always moves towards the boundary with a lower drainage capacity. In the end, an example of a four-layered soil is calculated to demonstrate the advantage of conducting the optimal design of horizontal drain. Remarkably, the rate of consolidation with the optimal implementation of horizontal drain is faster than the conventional design with horizontal drain at the mid-height.