Some History

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 1.2 shows a cross section of a high quality Roman road. It illustrates that its designer:

A. R. Dawson

University of Nottingham, Nottingham, UK e-mail: andrew. dawson@nottingham. ac. uk

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_1, © Springer Science+Business Media B. V. 2009

Summa crusta — grouted polygonal flagstones on best roads or rough cobbling ongood roads, absent elsewhere

Nucleus — compacted sand/gravel mix I++1 ®tatumen — larger stones sometimes

sometimes set in a pozzolanic mortar set in a mortar. Usually absent

Rudus — stabilised rubble and [—— 1 Agger — stone and soil earthworks to

stones < 50mm in size • * • lift road above surrounding ground

Some History

Fig. 1.1 Roman principal road network (Lay, 1992). Reproduced by permission of M. G. Lay

 

• provided cross-fall to help shed surface water to the margins rather than to soak in,

• raised the pavement well above the groundwater level of the surrounding ground so as to keep the amount of water in the embankment low and the effective stress (and, hence, soil strength) high,

• provided lateral ditches to prevent water table rise in wet periods and to convey draining water away from the construction.

 

Polygonal flagstones / rough cobbling

Edge stone sometimes cemented

in place as restraint

 

Typical

Dimensions

 

>2000

 

Vierteagus-

Longitudinal

drain

 

Natural formation

 

 

7500

 

Fig. 1.2 Cross-section of a high quality Roman pavement (dimensions in mm)

 

Some HistorySome History

Only a small proportion of pavements were built as illustrated, more generally a two layer pavement, comprising nucleus and rudus as explained in the notes to the Figure, was constructed on an embankment (agger — see Fig. 1.2). Despite the econ­omizing on materials, the aim of keeping the construction well-drained remained unaltered.

It was not until the late 1700s and early 1800s that a similar understanding was once again developed. Figure 1.3 shows a cross-section of a main coach pavement as designed by Thomas Telford, the Scottish engineer who worked in the UK and other European countries between about 1800 and 1830. In this design an effort has been made to provide a relatively impermeable surface to prevent water infiltration and a drainable foundation, but the route to lateral drains from these is not well developed.

Despite these early evidences of the understanding that drainage is needed for a well-functioning road, the lesson hasn’t always been fully appreciated. Arthur Cedergren, the American engineer, famously said that “there are three things that a road requires — drainage, drainage and more drainage” (Cedergren, 1974, 1994). He said this many years ago yet, despite many advances in the subject and a huge rise in environmental concerns since he was active, little further has been published in the area. This book is our attempt to redress that omission.

Some History

Fig. 1.3 Facsimile ofTelford’s design for a road from Warsaw to Brzsec1 (Telford, 1838)

1 The text at the top of the figure reads “POLISH ROAD / Transverse Section of the Road between the City of Warsaw and the Town of Brzesc in Lithuania. / This Road (100 English Miles) was constructed by command of the Emperor Alexander I. and finished in May 1825.” Nowadays, Brzesc is known as Brest, and forms the border crossing town between Poland and present day Belarus. It lies about 215 km East of Warsaw (Warszawa) not “100 English miles” ^ 160 km as indicated in the figure.

In the following sections the modern manifestation of the same objectives — to keep pavements dry by limiting ingress and assisting drainage — are introduced. Alongside this updating of the age-old principle of drainage, the modern pavement engineer or geo-environmentalist has to consider the quality of the draining water. What chemical components does the water contain? Is that a problem? Where will they go? The following sections seek to introduce this modern concern as well.

Updated: 11 ноября, 2015 — 7:36 дп