As indicated previously, subgrade drainage is designed to handle surface water inflow, whereas subdrains are designed to accommodate encroaching groundwater. Surface water can enter the pavement subsection through joints, cracks, and infiltration of the pavement. Rapid drainage of the pavement structural section is necessary to minimize piping and swelling of the subgrade material, and the subsequent increased deflections and cracking of the pavement surface. This rapid drainage can best be achieved by placing a highly permeable drainage layer under the full width of the pavement and allowing it to drain the infiltration to an edge drain. Figure 5.10 illustrates edge drain designs using either a pipe (perforated or slotted) in a trench filled with a permeable material, or a geocomposite panel drain.
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(b)
FIGURE 5.10 Typical pavement edge drains. (a) Pipe edge drain; (b) geocomposite panel drain.
