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Last update 30/05/2007

Task 2_6:- “Road Drainage”

Lead Contact

Geir Berntsen from the Public Roads Administration in Norway

Timo Saarenketo from Roadscanners Oy, Finland.

Objective

This Report aims to provide an insight into the state of the art of road construction and road maintenance for roads constructed across peat in the Northern Periphery of Europe.

It will concentrate particularly on the problems due to inadequate drainage and the best (current) practices for improving drainage in the four specific Partner Areas of the EU Roadex Project i.e. Troms County in Norway, the Districts of Keski-Suomi and Lapland in Finland, Region Norr of Sweden and the Highland Area of Scotland.

In addition, where considered appropriate, the report will also refer to relevant information concerning drainage and related experiences from elsewhere in the world.

A part of this report was written on the basis of a questionnaire on drainage problems in the Partner areas.

Outputs

This report focuses on the problems that inadequate drainage causes for low volume traffic roads in the Northern Periphery area of Europe.

A literature review has been done on moisture content in the road structure and the relationship between moisture content and characteristics for unbound granular materials and subgrade soil. It is obvious that increased moisture content reduces the bearing capacity and changes are greatest in dense materials with a high content of fines.

Typical drainage problems in the NP-area have been addressed and proposals on how to improve the problems are made. Many of the problems are the same all over the NP-area except for in Scotland where there are problems caused by grass verges on the road shoulder.

Field observations of roads on sloping ground shows that there are big differences in rut depth and roughness on the road cut side of the road compared to the embankment side. The ground water table was much closer to the road surface in the road cut lane and therefore there was also a higher moisture content in the road structure materials and the subsoil. For 20 % of the analysed roads the rut depth in the road cut lane was 1.5 times deeper than the other lane. Just 12 % of the roads had greater rut depth in the embankment lane.

Prediction models have been used to demonstrate that the lifetime of the pavement structure (calculated as number of standard axles) will increase considerably when drainage is improved. The Swedish design system has, among others, been used to calculate some examples and by improving only the drainage the lifetime will increase by a factor of 2.2-2.6 times.

All other prediction models show the same or an even greater effect. Both field observations and prediction models show that improving the drainage will increase the pavement lifetime. On the basis of the observations and models, a table for estimating the increase in lifetime when the drainage is improved is presented.

In this paper the life cycle cost calculations, made only for one pavement life cycle, show that both drainage maintenance and improvements of the drainage system will reduce the life cycle costs. There may be no other road condition improvement measures that are more profitable that can be done on an existing road.

The conclusion is that maintaining the drainage system is cost effective and must be prioritised among other maintenance activities. The first step in strengthening a road should be to make the drainage system function properly and this should be done 1-2 years before paving.

Links

Roadscanners Oy

Acknowledgments

The authors would like to thank Johan Ullberg, Sweden, Geoff Potter from Scotland and Taina Rantanen from Finland for answering the questionnaire and for the input to this report. A major contribution to this report was made by Sami Kari from the Technical University of Tampere who has made a comprehensive literature review on the subject.

This report was written by Geir Berntsen from the Public Roads Administration in Norway and by Timo Saarenketo from Roadscanners Oy, Finland.

Finally the author would like to thank the ROADEX II Steering Committee for its encouragement and valuable guidance in this work