Page 173 - RoadCem Manual - PCT BV

6.2.6 Shoulders
Construction of shoulders needs to be undertaken carefully if typical drainage problems are to be avoided. Preferably, the granular base should extend to the embankment slope with sufficient height above the ditch to prevent water intrusion. Trench, canal or “bathtub” construction, in which the pavement layers are confined between continuous impervious shoulders, should be avoided as this has the undesirable feature of trapping water at the pavement/ shoulder interface and inhibiting flow into the drainage ditch.
Shoulder materials should be selected which have a permeability similar to that of the base course, so that water does not get trapped within the pavement.
However, the material properties for unsealed shoulders may well be different from those required for the base for reasons of durability. Unsealed shoulders are similar to a gravel wearing course and require material with some plasticity, which is a property that might be considered less desirable for road base material.
A common problem is water infiltration into the base and sub base, which occurs for a number of reasons as, illustrated in Figure 6.8. These include:
• Rutting adjacent to the sealed surface.
• Build up of deposits of grass and debris.
• Poor joint between base and shoulder (more common when a paved shoulder has been added after initial construction).
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