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Proper Drainage Around Pavement

An Important Concept

The collection and diversion of surface drainage away from roadways, parking lots, and sidewalks is extremely important to good performance of pavements.  The subsurface and surface drainage systems should be carefully designed to ensure removal of the water from paved areas and subgrade soils.  Allowing surface waters to pond on pavements will cause premature pavement deterioration. 

A primary cause of early pavement deterioration is water infiltration into the pavement system.  The addition of moisture usually results in softening of the supporting soil and the eventual failure of the pavement.  Any drainage design should include ways to rapidly remove surface runoff.

Curb and gutter should be backfilled and the backfill compacted to reduce ponding adjacent to pavements.  Final grading of the subgrade of pavements should be carefully controlled so that surface slopes are maintained and low spots in the subgrade which could trap water are eliminated.  Seals should be provided between curb and pavement and at all joints to reduce moisture infiltration.  Landscaped areas and detention ponds in paved areas should be avoided.

AASHTO is the Top Authority on Pavement Design


American Association of State Highway and Transportation Officials (AASHTO), Guide for Design of Pavement Structures provides the following guidelines and criteria for maintaining good drainage around pavements:​Drainage of water from pavements has always been an important consideration in road design; however, current methods of design have often resulted in base courses that do not drain well.  This excess water combined with increased traffic volumes and loads often leads to early pavement distress in the pavement structure.And;Water enters the pavement in many ways, such as through cracks, joints, or pavement infiltration, or as groundwater from an interrupted aquifer, high water table, or localized spring.  Effects of this water (when trapped within the pavement structure) on pavements include:(1) reduced strength of unbounded granular materials,(2) reduced strength of roadbed soils,(3) pumping of concrete pavements with subsequent faulting, cracking, and general shoulder deterioration, and(4) pumping of fines in aggregate based under flexible pavements with resulting loss of support.Less frequently noticed problems due to entrapped water include (but are not limited to:(1) stripping of asphaltic concrete,(2) differential heaving over swelling soils, and(3) frost heave.And;Methods for treating water in pavements have generally consisted of:(1) preventing water from entering the pavement,(2) providing drainage to remove excess water quickly, and(3) building the pavement strong enough to resist the combined effect of load and water.When all possible sources of water are considered, protection of the pavement structural section from water entry requires interception of groundwater as well as sealing of the pavement surface.  Considerable attention has been given to intercepting groundwater; whereas less attention has been given to sealing the surface to exclude infiltration from rain and snow melt.  As a result, a considerable amount of water often enters the pavement substructure, resulting in a need for some type of drainage.And;To obtain adequate pavement drainage, the designer should consider providing three types of drainage systems: (1) surface drainage, (2) groundwater drainage, and (3) structural drainage.  Such systems, however, are only effective for ‘free water.’  Water held by capillary forces in soils and in fine aggregates cannot be drained.  The effects of the ‘bound’ moisture must be considered in the design of pavement material properties.  Most existing pavements do not include drainage system capable of quickly removing free water.Most existing design methods have relied on the practice of building pavements strong enough to resist the combined effects of load and water.  However, they do not always account for the potential destructive effects of water within the pavement structure.  As a result, increased emphasis is needed to exclude water from the pavement and provide for rapid drainage.

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