Since the construction of early paved roads some 100 plus years ago, it quickly became evident that drainage was the number one element that must be addressed in assuring the long-term performance of roadways. Today, drainage is designed into and encompasses multiple parts of our roadway systems. These drainage systems are defined as two categories: surface and subsurface drainage systems.
Surface drainage systems are the large water movers that are designed to transport, channel and/or collect surface water from streams, slopes and road surfaces. Surface drainage systems include intercept ditches that divert water and prevent it from reaching the road and roadside ditches (transportation ditches) that carry water away from the road. Curbs, gutters, deck drains, slotted drains and drop inlets are designed to remove surface water from bridges and pavements. Culverts, cross drains, storm drains and entrance pipes are used to transport, channel and/or collect water and move it away from the roadway.
Subsurface drainage systems are designed to collect subsurface water that, when left in place, can cause unstable embankments and premature pavement failures. Subsurface systems consist of deep embankment drains to remove water from within large fills, perforated cross drains to remove troubled water spots and shallower under drains (edge drains) to remove water from within and under the pavement structures. Subsurface drainage systems also include bridge end drains and wall drains designed to remove water from under and behind large structures such as bridge end bents, bridge approaches and retaining walls.
As previously mentioned, under drainage systems are an integral portion of the roadways, and are the number one element that must be addressed in assuring the long-term performance of our roads. It is critical that these systems be properly designed, construction, inspected and maintained. Improper design, construction and maintenance can significantly reduce the life of the roadway and can cause dangerous/life-threatening conditions for motorists.
Quality control specifications are on the rise across the nation for highway drainage systems. As a result of poor culvert performance in several states, the American Association State Highway and Transportation Officials (AASHTO) recently added video inspection requirements to their new standards for culvert pipe structures. The new standard will address deflection in flexible pipe structures and cracking in rigid structures. Until recently, these structures have gone relatively unchecked in that they have not undergone any post construction inspection.
Video inspection of the smaller 4-in. under drains has been a common practice by several DOTs since the mid 1990’s after numerous pavement failures resulting from damaged drainage structures. DOTs found that 40 to 50% of their subsurface drainage systems were not completely functional. Drain video inspection standards today typically require the system to be videoed prior to the final surface being placed. Any observed distress is repaired at the contractor’s expense.
These quality control specifications are also impacting design and construction procedures. DOTs and contractors are opting to go with higher-grade outlet pipes and better backfill to reduce induced construction damage. In addition to constructing a more robust system that will pass more stringent quality control tests, designers and owners should specify systems that will reduce future maintenance cost and look at the long-term cost benefits of specified and selected materials.
Research conducted by the Kentucky Transportation Center indicates that a properly installed and maintained under drain system will increase the life span of the road by approximately 10 years.
With the onset of more stringent installation and performance specifications, new technologies are being utilized and are becoming readily available to assist the engineers in evaluating not only new construction but also our aging infrastructure.
New camera and inspection technology is quickly being evaluated and adopted by DOTs to provide quality assurance of storm drains and cross drains on new construction projects. High-resolution pipeline inspection cameras with low barrel distortion and high intensity lighting are being utilized to provide a continuous detailed video inspection in pipeline drainage structures.
It is evident that crack widths, joint separation and pipe deflection can not be determined with pipeline video inspection cameras alone, but must be partnered with image processing technology.
Pipeline inspection cameras are being equipped to work with video micrometers to measure cracking in rigid structures and laser ring technology to provide continuous internal profiles and deflection analysis.
Our aging infrastructure
Roadway infrastructure is expanding at a rapid rate, and the older infrastructure built in the late 1940’s through the 70’s is aging. Some problems due to this aging in our road surfaces have been addressed over the decades, but little has been done with our roadway drainage systems.
A paper published by the Transportation Research Board in 2004 entitled “The Economic Costs of Culvert Failures” discusses the total cost, including emergency replacement cost and user delay cost of various culvert failures throughout the U.S. and Canada. Emergency replacement cost ranged from $90,000 to $4,200,000, and estimated user delay cost ranged from $870,000 to $15,099,000. Consider the possible economic impact a major culvert and roadway failure would have on our busier interstates, parkways and major connectors.
A recent study conducted by the Kentucky Transportation Center for the KY DOT evaluated approximately 830 (30 to 50-plus-year-old) cross drain structures. Of these 830 structures, approximately 313 (37%) needed remedial action, 134 (16%) needed repair work (isolated point repairs, lined or replaced) and 179 (21%) needed to be cleaned and possibly repaired.
In evaluating various rail failures and road slope failures in Kentucky, it was found that faulty cross drains were the possible cause or a contributing factor to the unstable conditions. Large slope embankment repairs can range from tens of thousands of dollars to as high as $1.5 million. Several of these failures could have been prevented through measures such as better quality control specifications and periodic maintenance inspections.
With the new interest by many DOTs in evaluating and repairing the existing infrastructure, new cleaning and lining technologies are also becoming more widely available. Technologies have been developed utilizing directional drills to clean large rocks and other debris from cross drain structures. This technology is quickly being adopted into the highway and rail industry throughout the U.S.