Geotextiles and Geomembranes 22 (2004) 37–48 Discharge capacity of prefabricated vertical drain and their field measurements M.W. Bo* Bullen Consultants Ltd., 11/12 Eldon Place, Bradford BD1 3AZ, UK Received 20 February 2002; received in revised form 11 April 2003 Abstract Discharge capacity is the most important parameter for performance of prefabricated vertical drains. However, the required discharge capacity for best performance of vertical drain is still uncertain. This paper described the single basic equation to obtain the required average discharge capacity. The estimated values were supported by the field measurement of discharge capacity with different drain spacings, different penetration length and different thickness of compressible layers. It was found that required discharge capacity is in an order of 10 6 m/s for 100mm width drain. r 2003 Elsevier Ltd. All rights reserved. Keywords: Discharge capacity; Hydraulic gradient; Prefabricated vertical drain; Confining pressure; Deformation 1. Introduction Discharge capacity is important parameter that controls the performance of prefabricated vertical drains (PVD). Only PVDs having sufficient discharge capacity can function well. There are two major uncertainties related to the discharge capacity of vertical drain. The first one is the determination of the required discharge capacity ðq w Þ to be used in design (Holtz et al., 1991). Estimation of required discharge capacity was proposed by various researchers (Mesri and Lo, 1991; Kamon et al., 1994; Den Hoedt, 1981; Kremer et al., 1982; Holtz et al., 1991; Bo et al., 2000). Another is the measurement of the discharge capacity of the drain in laboratory and the field. The first problem is the variation of discharge capacity with ARTICLE IN PRESS *Tel.: +44-1274-370410; fax: +44-1274-734447. E-mail address: mwb1@bullen.co.uk (M.W. Bo). 0266-1144/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0266-1144(03)00050-5