Keeping Roads Dry
by Clare Coppa
Clogged drains can turn highways into ice rinks. State officials from New York and Texas describe how ASTM standards for geosynthetics and plastic pipes support safe highways.
L. David Suits is supervisor, Soils Engineering Laboratory, New York State Department of Transportation Geotechnical Engineering Bureau, Albany, N.Y., and chairman of ASTM Committee D35 on Geosynthetics.
The D35 standards apply to all forms of geosynthetics used in the construction of transportation facilities, says Suits. The geosynthetics of concern as related to drainage include geotextiles, geonets, and geocomposite drainage materials. The critical questions that need to be answered when considering the use of these materials is: How will they perform?, and How do I know if I am getting what I specified?
That is where the D35 standards come into the picture. As related to drainage, they provide information as to the ability of the geosynthetic to transmit water, retain soil, and survive installation and design stresses. They also provide the engineer with simple material properties such as mass/unit area, and thickness which can be used a quick quality assurance check on the materials.
Drainage plays some role in almost all applications using geosynthetics in highways, continues Suits. Water within the pavement system is a primary cause of deterioration, and loss of pavement life, as well as the cause of unstable slopes along the highway, or embankments on which the highway is placed.
Geosynthetics used in edge drains under the shoulder sections of pavement carry water, which drains from under the pavement, away from the pavement, thus creating a more stable base on which the pavement rests. As a separator between the in-situ soil, and the drainable base section of the pavement system, it allows water to escape, while preventing the base materials from becoming clogged with the finer in-situ soils. In both scenarios, before the advent of geosynthetics, much more costly solutions, such as graded aggregate filters, were used to address the problem of drainage.
Gary N. Oradat is deputy director, Engineering, Construction and Real Estate Division, City of Houston, Texas, Department of Public Works and Engineering and chairman of ASTM Committee F17 on Plastic Piping Systems. When F17 standards are used for highway construction, Oradat says, more specifically the culverts which are installed underneath highways, transportation officials can be assured that the pipe will perform as intended. F17 standards (i.e., specifications, practices, test methods, etc.) ensure uniformity in pipe design, manufacturing, installation and/or acceptance testing.
A typical scenario would be a drainage culvert for highway, frontage road, etc., he says. Its unusual for water and/or sanitary sewer lines to be within the right-of-way for highway construction, but in those instances where it does happen, designers can be assured that the pipelines will perform and provide an enviable service life.
Copyright 2003, ASTM