The A11 Thetford Bypass comprises approximately 7.5km of single and double carriageway. The design called for a roadside fin drain system to act as a vertical water flow interceptor in conjunction with a horizontal under channel drainage layer incorporated within the roadbase. The combined system discharges to conventional drainage outlets.
Filtram 1B1 -ED was chosen as the vertical fin drain and installed following the placement of capping and subbase layers. The trench, 200mm width, was excavated using conventional machinery - a JCB and narrow width bucket. Filtram was supplied in 12m lengths complete with nom. 100mm perforated polypropylene Aqua pipe meeting D.Tp. requirements.
Filtram 1 BZ was used as the under channel drainage (D.Tp. Highway construction detail) positioned horizontally on the subbase, directly beneath the slip formed concrete roadside channel. In addition a Terram wrapped Aqua-pipe (D.Tp. Highway construction detail) was used in this construction.