The demanding role expected of drainage culverts is to ensure the control of free-flowing water, guarding against flooding and soil displacement. Culverts complement the creeks and channels that intersect roads and highways, rural driveways, runways, and paths, enabling safe and easy auto crossing.
An engineered drainage plan may include several types of drainage structures, usually combining natural flow channels with culverts—sometimes called “cross drains” because they facilitate waterway crossings. Careful planning is required to establish correct sizes, lengths, and end treatments of buried culverts to achieve the site's storm-water management objectives. Good design also involves selecting culvert materials with a history of value and dependability.
For more than a century, more than a third of the drainage culverts installed in the United States have been corrugated steel pipe (CSP) in round and pipe-arch shapes. The popularity of CSP drainage culverts relates to their value and durability, the latter benefiting from enhanced corrosion resistance for service life expectancies of 75 years or more. A variety of protective coatings and linings allow designers to match CSP materials and site conditions for optimum reliability.
Care and Maintenance
The assurance of long-term storm-water control by a drainage system depends on care and maintenance. Any impairments, such as damaged or aging components, will hinder the drainage process and can result in property damage.
According to Brent Brewbaker, P.E., vice president of marketing for corrugated metal pipe for West Chester, Ohio-based CONTECH Construction Products Inc., keeping culverts working starts with routine inspections. “While an inspection program will not ward off the common effects of aging, it provides adequate forewarning about any remedial needs,” he said.
Most factors affecting the permanence of buried culverts are related to changes in the post-construction service environment. Some concerns include increased volume of stormwater directed to the culvert, chemicals and debris transported by runoff water, damaged or modified culvert inlet or outlet structures, changes in soil chemistry, and stray underground electric currents. Other matters affecting performance include more obvious things like trash and brush accumulations in the culvert and excessive vegetative growth at pipe ends.
Inspection and Rehabilitation
A regular inspection and maintenance program will keep culverts free-flowing and provide early notice when attention is needed. When inspection reveals signs of distress, such as excessive invert wear, the most practical response is early rehabilitation.
Drainage culverts are one of many civil infrastructure systems benefiting from rehabilitation techniques that allow in place restoration in lieu of replacement. “Corrugated steel drainage culverts are one of the easiest infrastructure items to maintain and rehabilitate,” said Ben Pocisk, manager of corrugated metal pipe products for CONTECH. “The most popular rehabilitation technique involves inserting a steel or plastic pipe within the existing pipe—a process called ‘sliplining'—to restore reduced flow capacity and protect the culvert's load-carrying capacity. The typical relining process involves little equipment and personnel and can be accomplished without disturbing the surface, which permits uninterrupted traffic flow.”
Pocisk adds that the most suitable liner materials have proven to be spiral-rib steel or PVC pipe; both have smooth interior surfaces and profile wall (ribbed) exteriors that offer better deflection control and are easier to install. Cement grout usually is used to fill the void space between the existing culvert and the new liner pipe. Spiral rib pipe's longer individual lengths and fewer secure joint connections facilitate easy installation in steel culverts.
All types of pipe culverts, including concrete and plastic, should undergo periodic inspections. Preventive care is the best way to achieve long life. Virtually all culvert failures result from insufficient maintenance or unidentified harmful changes in service conditions. If the need arises, the hydraulic performance of buried culverts typically can be restored with liners. The characteristics of corrugated steel culverts make relining relatively fast and economical, saving the cost of excavation and replacement without sacrificing drainage capacity.
— Ted DeVilbiss is senior vice president of sales for CONTECH Construction Products Inc., and board member of the National Corrugated Steel Pipe Association.