A Rational Approach to the Design of Vertical Drains Considering Soil Disturbance

Abstract

This paper presents analytical solutions for the rate of consolidation by prefabricated vertical drains (PVDs) that take into account the properties of soft, clayey soils, the disturbance in the soil surrounding the PVD caused by the installation process, and PVD dimension and spacing. A particular feature of the analysis is that it rigorously takes into account the spatial variability of the soil hydraulic conductivity of the disturbed soil mass around the PVD. Design charts are developed based on the analytical solutions that can be used to determine PVD spacing without requiring any iteration. A numerical example is provided that illustrates the design procedure. INTRODUCTION Thick alluvial deposits of soft clayey soil are characterized by low shear strength, high compressibility and low hydraulic conductivity. Pre-treatment of these deposits by the installation of prefabricated vertical drains (PVDs), often in conjunction with preloading, is a popular practice in geotechnical engineering. The installation of PVDs generates hydraulic gradients that drive the pore water out of the deposit through the PVDs and into a drainage blanket. Because PVDs are installed with a close horizontal spacing of about 1 to 3 m, the drainage path inside the soil is greatly reduced and consolidation of the soil deposit is accelerated (Holtz 1987). There are some operational problems associated with PVDs. One such problem arises from the disturbance caused to the ground during installation of the PVDs. Due to this disturbance, the hydraulic conductivity of the soil surrounding the PVD decreases significantly from the in situ value, slowing down the consolidation process. Therefore, the effect of soil disturbance must be taken into account in PVD