Overview
The federal guideline for water protection from road runoff entitled "Gewässerschutz bei der Entwässerung von Verkehrswegen" published by the Federal Office for the Environment FOEN was analysed specifically regarding the design of infiltration over the road shoulder. Information was gathered, e.g. information about priority of measures and modern drainage concepts. Furthermore, expert knowledge on common layouts of infiltration over the road shoulder, and on soil filters with infiltration into the ground, e.g. into the road slope was collected. This research set the basis for the
Swiss Standard SN 640 354, Strassenentwässerung, Entwässerung über das Bankett.
The project has 2 crucial objectives:
- To adjust the flow problem and infiltration of ground water. Collect all the information resulting from recent and ongoing research, regarding constitution of the aisles, supplemented by existing achievements in analysing and adding innovative solutions while taking account of the criterion cost / benefit.
- To prepare the technical basis and give examples for the design and the practical and hydraulic design:
- Various types of seats, shoulders and side adjustments
- Slope and infiltration works.
For research to meet the objectives, the methodology should be able to:
- To incorporate the results of the two research mandates No. 2001/202 and No. 2001/203, particularly with regard to the possible structures of the aisles, building embankments, problems with the purifying soil protection, springs, groundwater mats, operation and maintenance
- To take into account the knowledge acquired abroad, particularly in France, Germany and Austria
- To ensure implementation of the 'Instructions: Water pollution in the drainage channels of communication "SAEFL 2002
- To give constructive guidance on various embodiments of aisles
Funding
Results
The most important conclusions are as follows:
- The road shoulder can be constructed with an impervious or pervious pavement.
- For road shoulders with impervious pavement it is recommend to using clayey surface course, or a layer of material stabilised with cement, which is only partially impervious.
- Pervious road shoulders can be constructed with gravel turf, gravel turf with grid, and grid pavers.
- The highest priority should be on using clayey surface course.
- It has to be proven that the material used for the construction of clayey surface course is suitable. A mix of gravel, sand, and clay must not be used under any circumstances.
- Soil horizon A (topsoil) and B (subsoil) are used to build a soil filter. The soil horizon A should be 0.25 m thick, or under special circumstances up to 0.30 m. The thickness of the soil horizon B depends on local situation and soil characteristics, and has to be carefully
- The humus proportion of soil horizon A must be at least 4%, the clay proportion should be between 10% and 30%, ideally 25%, and the silt proportion should be maximum 50%.