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Based on their ambient material, aquifers can be classified into three types, i. e. open, A confined aquifer is bounded both above and below by relatively impermeable materials or confining beds (such as clay or unfractured rock.) The confined water is under pressure thus a tube extended from the surface down into the aquifer would allow the water to rise inside the tube to a level above the top of the aquifer.
• An open aquifer is one without a confining bed above so it can be directly recharged by rainfall.
• A semi-confined aquifer is a confined aquifer where one of the confining beds is saturated material with low permeability which, thus, impedes the movements of the water.
Most road structures or road embankments can be considered open aquifers. Only under some special circumstances do they act as a semi-confined or confined aquifers.
For pavements and their relation to groundwater (from the geometrical point of view) perched-type aquifers are of importance. These aquifers are the consequence of some lower permeable lenses (e. g. clays) inside a permeable aquifer. As a consequence of a high coefficient of permeability of the aquifer material and favourable infiltration into the ground, water mounds appear above the lenses. These aquifers have no direct connections with lower lying groundwater. Usually they are very near the surface and may cause several problems for the construction and maintenance of the roads.
