15 March 2001
12.1. Purpose. Water is a fundamental factor in most problems associated with pavement
performance and is responsible directly or indirectly for many of the distresses found in pavement
systems. One of the most prevalent sources of pavement distress is the loss of support to the
pavement structure caused by removal of underlying fine-grained material by pumping. The
infiltration of water through the pavement causes saturation of the base and subbase. When
traffic loads are applied, pumping occurs unless these pavement systems are very porous and
able to quickly remove the water from the system. Repeated cycles lead to loss of support for the
pavement structure with deflection and cracking (Figure 12.1.).
12.2. Need for Pavement-Edge Drainage. Pavement-edge drainage may be required where:
12.2.1. Surface drainage facilities within the vicinity are inadequate.
12.2.2. Water table may rise.
12.2.3. Surface water may enter the pavement system at joints or cracks, at the edges of the
surfacing, or percolate through the surfacing and shoulders.
12.2.4. Water may move vertically in capillaries or interconnected water films.
12.3. Drainage Systems. Drainage systems consist
of two major classifications: surface
subsurface. When both types are required for efficient maintenance and protection of the
pavement, it is generally a good practice for each system to function independently.
12.4. Subsurface Drain Functions. Subsurface drainage
is provided to: intercept, collect, and
remove any ground water from the subgrade or base, lower high water tables, drain water