Pavement sub-surface drainage lies at the boundary of several disciplines each having their own special terms and notations. The book does not avoid these but, rather, seeks to define them when they are used. To help readers, a “Glossary” is included (Annex C) as well as a list of terms in several languages (Annex B) and a list of symbols (Annex D).
Water and road construction do not make for a harmonious couple! While water is needed to allow efficient compaction of most of the earthworks and pavement layers and some moisture held in pores can act to develop strengthening suction due to capillarity effects, the overall picture is that water in the road and road sub-structure is undesirable. Water should, if possible, be kept out. If that is impossible (and it usually is impossible to achieve this) then efficient drains must be provided to convey the water away from the loaded areas. To bring about this happy condition, the road engineer has to understand about the response of pavement and geotechnical materials in the presence of water, about flow routes, about the drivers of water movement — climatic and hydrogeological — about the contaminants that can be moved in the water and about the regulatory framework in which he or she is obliged to operate. To successfully and economically deliver a well-behaved road is not easy to do. Therefore the following chapters aim to provide basic and more advanced information in all these areas. Not only do they aim to help the hard-pressed road engineer, but also to provide environmental engineers, hydrogeologists and others with a "language" in which to address the topics that have such an impact on every road user — on all of us!
