Effect of hydraulic radius on long-term drainage capacity of geosynthetics drains

The results of the long-term drainage capacity of four types of prefabricated vertical drains (PVDs) and three types of prefabricated horizontal drains (PHDs), and as well of the transmissivity of a dual function (reinforcement and drainage) geotextile (DFG) are presented. PVD, PHD and DFG are together called geosynthetics drains in this study. A method of calculating the hydraulic radius (R) (cross-sectional area divided by the perimeter of a drainage channel) of PVDs and PHDs by considering the deformation of the filter (under confinement) is proposed. Based on the limited test data, it is found that the rate of water flow per unit drainage area, q, increases with the hydraulic radius of the drainage channel, thereby q is approximately proportional to R-1.2 and R-1.7 for elapsed times of 1 and 3 months, respectively. Including the results of the DFG (R-value is close to zero), the drainage capacity ratio (r), defined as the value at time t divided by the corresponding initial value (t = 0) increases almost linearly with the R-value. It is recommended to employ geosynthetics drains with a larger R-value, i.e. a stiff filter, a strong core, and large and square-shaped drainage channels. (C) 2003 Elsevier Ltd. All rights reserved.