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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 repo...

In Europe road construction may date back as far as 3,500 years ago. These early roads were probably largely for ceremonial purposes, over short distances, and may have carried little, if any, wheeled traffic. It was not until the growth of the Ro­man Empire that a large network of engineered pavements was first constructed (Fig. 1.1). Such was the desire to secure the Empire against enemies and to enhance trade that, at the peak time, about 0.5 km was being built daily. Although foot and hoof traffic probably predominated, those roads were certainly used for wheeled vehicles too.

The engineers responsible for these pavements understood some important truths about pavement drainage – truths which, in practice, sometimes are still not recog­nised today. Figure 1...