In road rehabilitation, it is important to design the drainage at the same time as the other rehabilitation measures (e. g. strengthening of the structure). The designer should aim to recognise locations where poor drainage is the major cause of road damage. In cold regions the springtime is usually the best time for field studies of the drainage system, since the water level is high, frost damage can be seen, vegetation is low and the bearing capacity and slope stability are lowest. Very wet/soft slopes can indicate a wet structure. There may even be water pressure inside the structure, as in Fig. 13.45 where water is pouring out from the slope of a highway just before a culvert (which is acting as a water barrier).
The appearance of certain vegetation (e. g. rushes and willow trees) on the slopes can also be a sign of excess moisture in the geotechnical structures, appearing typically on low permeability slopes. Video or photos can help to record the conditions. Ground radar surveys may also be used to identify extra moisture on
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Fig. 13.45 Water exiting from an embankment slope where it has collected due to a culvert (in the background) acting as a barrier |
road structures and in subsoil or on rock surfaces and the level of the groundwater. Bearing capacity measurements can be used to identify weak (moist) locations and rock locations (maybe channelling water) below the road. The designer should analyse available observations, measurements and the requirements for both the road and its surroundings.
