What is meant by pavement drainage?

Pavement Drainage holds ample significance, as it prevents the accumulation of water or any liquid on the surface of pavements and ensures proper drainage system. With proper design and gradual slopes provided, the water gets easily removed from the surface into the drains, which are essential during heavy rains and unusual weather conditions keeping it less prone to accidents and increasing the durability of the pavement structure.

History of pavement drainage

Romans were the first pioneers when it came to building structures, planning, and constructing long-lasting roads. But as this concept came into existence, engineers recognized the absolute necessity of a proper drainage design of pavements that can resist harsh weather, traffic volumes, and hassle-free experience over long journeys.

The pavement designers are required to understand and examine the conditions under which the pavement structure has to function for appropriate pavement design. Pavement or highway geometrics, non-pavement subsurface drainage, surface drainage, climatic conditions, sub-base rainwater, and various soil properties, everything has a powerful impact on the drainage design. With the previous information, the designer is capable of predicting the free water amount that enters the pavement structure, predicting surface free water runoff; and establishing the moisture content of the design sub-grade.

The main source of water in pavements is usually rain and it may enter the pavement structure through many ways like infiltration, cracks, penetration from shoulders and ditches, higher groundwater level and so on, the water can also be moved by certain energy gradients, like capillary forces, shear pressure differences, and so on which, in turn, seeps into the sub-grade.

By a combination of various equations and principles, the criteria that are selected have an ample amount of influence over the equations used. Thus, the drainage criterion needs to be selected cautiously. The material specifications have to be checked so that all the permeability, strength, load distribution, and construction stability requirements are met.

Types of pavement drainage

Surface drainage

The surface drainage includes the removal of all water that is present on the pavement surface and nearby area or from other surfaces through which the water can flow elsewhere but has no relation with underneath layers and the permeable base. The water needs to be disposed of off in an orderly manner to avoid accumulation underneath and prevention of pavement weakening. Three major ways used to stop water collection and infiltration are impermeable HMA (Hot Mix Asphalt), grade, and slope.

Subsurface Drainage

Subsurface drainage is the disposal of water that penetrates inside sub-base pavement layers, permeable base and, nearby soil. This water can enter through the adjacent porous substance, from the underground due to gravity flow or capillary rise action.

Hot mix asphalt pavements may tend to fail since the sub-grade support deterioration occurs due to extreme moisture content and various water-related issues. They can be avoided by minimizing water infiltration and providing a subsurface water drainage system of the pavement.

Pavement surface drainage design

For conservation of the pavement structure that is not full­-depth asphalt from the surface water-related action can be simply achieved by a full-width asphalt surface which means that the topmost layer of the pavement, inclusive of the shoulders, is made to provide an impervious covering that would prevent the surface water from entering the pavement from the sides and corners. On the embankment, asphalt spillways with the assistance of asphalt curbs or dikes receive the diverted water and these are made on the ends of the shoulder.

If a full-width asphalt surface is not used for some reason, the pavement designer must create alternative provisions to remove the water.

For conservation of the pavement structure that is not full­-depth asphalt from the surface water-related action can be simply achieved by a full-width asphalt surface which means that the topmost layer of the pavement, inclusive of the shoulders, is made to provide an impervious covering that would prevent the surface water from entering the pavement from the sides and corners. On the embankment, asphalt spillways with the assistance of asphalt curbs or dikes receive the diverted water and these are made on the ends of the shoulder.

If a full-width asphalt surface is not used for some reason, the pavement designer must create alternative provisions to remove the water.

Methods for surface drainage system control

Pavement Crown and Slopes

Pavements have to be built alongside a crown or a slope to divert water flow from them. The most frequently used design practice allows the surface water to flow over the shoulder structure into a drain or gutter present at the sides. Specifications of pavement design are given below:

Shoulder drainage

The best way is to waterproof the entire shoulder with an asphalt coating. This asphalt covering will prevent any water seepage. An alternative but minor method is to cover the shoulders with an aggregate grade to reduce the seepage into the sub-grade.

Curbs and dikes

In certain cases, a raised lip or curb whose height is four inches or more, may be made at the outside shoulder end to direct the flow and guide it to some desirable outlet

Medians

In modern multi-lane highways, wherever possible, this widespread median strip should be depressed and its valley must be lower than the sub-grade surface. If unfavorable, underdrains may be installed.

Roadside ditches

Similar to drains, they are built along the sides of the roadway to gather the runoff from the pavement surfaces and water from subsurface drainage in order to achieve a suitable drainage system. Sometimes they are semi-covered for safety purposes. V-shaped side ditches should not be used since they encourage erosion by concentrating water flow towards their bottoms where the water seeps inside the permeable base layer but if the capacity requirement is more then just widen the side ditches rather than deepening them.

Parking lot drainage design

Here, the most economical pattern must be chosen and after that, the drainage grades that remove patrons stepping from cars into ditches can be designed. Since the permeable base layer of the pavement is in existence, the stormwater runoff can be prevented and the untreated water can be collected and treated, if necessary, then used for other purposes like washing, watering plants, and so on. ASTM E2380 / E2380M - 15(2019) is exclusively used for reference in Standard Test Method for Measuring Pavement Texture Drainage Using an Outflow Meter.

To avoid any puddle formation during monsoon season, a minimum of 2% (1/4” per foot) grade is required for all the places used by the pedestrians.

Design considerations

• During the preliminary soil survey, decide the location of all the seepage areas that causes water to percolate the pavement.
• Determine the maximum flow rate of water which can enter the structural section from any cracks or joints and infiltration places.
• Locate an aggregate source suitable for filtration to avoid clogging of drains or silt deposition by soil
• Locate an aggregate source that, if required can be used as drain rock for disposal of the water underneath the pavement.
• Put together all these materials into an adequate capacity design to meet all the requirements for the long durability of the pavement

Context and Applications

The topic is taught in courses related to:

• Bachelors of Technology (Civil Engineering)
• Masters in Technology (Geo Technical Engineering)
• Masters in Technology (Transportation and Highway Engineering)

Practice Problems

Q1. Which of the following requirement(s) is/are required to be selected for the appropriate design of the pavement drainage?

1. Load-distribution
2. Permeability
3. Both a and b
4. None of these

Correct Option- c

Explanation: Load-distribution and permeability requirements are required to be selected for the appropriate design of the pavement drainage.

Q2. What are the two major types of pavement drainage?

1. Surface drainage and sub-surface drainage
2. Permanent sub-grade drainage and temporary sub-grade drainage
3. Impermeable base drainage and permeable base drainage
4. None of these

Correct Option- a.

Explanation: Surface drainage and sub-surface drainage are the two major types of pavement drainage.

Q3. Who was considered to have the latest knowledge about durable roads?

1. Greeks
2. Romans
3. Egyptians
4. Mughals

Correct Option- b

Explanation: Romans were considered to have the latest knowledge about durable roads.

Q4. The percentage slope (in %) for the shoulder structure should be within the range of?

1. 1 to 2
2. 2 to 3
3. 3 to 4
4. 4 to 6

Correct Option: d

Explanation : The percentage slope (in %) for the shoulder structure should be within the range of 4 to 6.

Q5. For what the ASTM E2380 / E2380M – 15, 2019 version used ?

1. The Standard Test Method for Measuring Pavement Texture Drainage Using an Outflow Meter
2. Consolidation and Pavement sub-grade Design
3. Building Design Codes
4. Paving Sub-grade Systems

Correct Option: a

Explanation : The ASTM E2380 / E2380M – 15, 2019 version is used for the Standard Test Method for Measuring Pavement Texture Drainage Using an Outflow Meter.

Related concepts

• Drainage Systems
• Pavement Drainage and Design
• Transportation Planning and Engineering
• Soil Mechanics