The main aim of this book is to increase the knowledge about water in the subsurface road environment so as to improve highway performance and minimise the leaching of contaminants from roads. Improvement of pavement performance will lead to less road closures, better use of the road network, longer service life and more effective transportation of goods and people.
This aim can be further divided into the following four secondary objectives:
• to describe the most up-to-date understanding of water movements and moisture conditions in unbound pavement layers and subgrades for different types of road constructions in various climatic conditions,
• to explain the relationship between the mechanical behaviour of materials/soils and their permeability[2] and moisture condition,
• to report on advanced modelling of water movement and condition in the subsurface pavement environment developed from laboratory analysis and field studies,
• to inform about the identification, investigation and control of contaminants leaching from soils, natural aggregates and by-products in the sub-surface layers.
It is important to add that this book is NOT about road surface drainage. There are many books that address this topic, e. g. Ksaibati & Kolkman (2006), whereas this book aims to concentrate on sub-surface water. Inevitably, there is some overlap between the two aspects but, in this book, the information on runoff is only that necessary to complete a coverage of the sub-surface condition. Regarding contamination, traffic is, of course, a significant source too (see Chapter 6, especially Fig. 6.1) but the reduction in contaminants from that source is beyond the scope of this book. Rather, the aim is to understand what happens, or should happen, to contaminants in the highway environment.
