Who thinks about culverts — those anonymous-like structures motorists traverse over daily without likely giving a thought to their age and condition or the general purpose?
Often overlooked and not routinely prioritized in maintenance and construction planning over the years, these ubiquitous, yet essential structures have been a part of our infrastructure landscape since the advent of the federal highway system during the 1940s and 1950s.
More than just part of the highways we travel on, culverts serve a critical purpose, as they allow water to flow under roadways, railroads, trails or any other obstructions. They are, in fact, also labeled by many Departments of Transportation (DOTs) as “bridges” in their official paperwork as these structures may be used as bridge-like structures to carry traffic. Taken for granted by the general population, structural deterioration or other damage to these structures can result in catastrophic road failures.
Back to the question of who thinks about culverts — DOTs do, or at least they have in recent years.
Trenchless methods have been a part of pipe rehabilitation and replacement for more than 40 years; federal mandates and consent orders have aided in this push over time, forcing owners and municipalities to address their systems. But culverts and other drainage structures have been a different tale and were virtually ignored during a time when sanitary sewer and water line repairs took center stage.
Culverts, as most of our underground infrastructure, are in dire need of attention as they continue to age and deteriorate. Slow to realize the benefits of trenchless technology for these structures, owners today are now turning to it to install new culverts or rehabilitate existing ones that can be saved.
We spoke with a few industry experts about the state of the culvert market and its place within the trenchless industry. All agree that trenchless technologies are playing an important role in this rapidly growing market sector, with one estimating that it holds up to 20 percent of the trenchless rehab market. This part of the trenchless market — often referred to as the “DOT market” — is on the rise.
“Almost 15 years ago, most major DOT and public works agencies began to recognize the importance of rehabilitating their underground infrastructure before or during these large resurfacing programs in order to avoid damaging newly paved roads,” says Ian Lancaster, senior vice president of sales at Aegion Corp. “Due to this change, trenchless technologies have experienced rapid, double-digit growth year-over-year over the past decade as the agencies continue to recognize the importance of rehabilitating underground infrastructure in their regular roadway replacement and maintenance programs.
“Currently, the rehabilitation of storm water pipelines and culverts is estimated to be 15 to 20 percent of the overall trenchless rehabilitation marketplace,” Lancaster notes. “This percentage could drastically increase over the coming years should agencies continue to recognize the importance of renovating underground pipelines/culverts and how this can offset their ever growing need to maintain failing roadways.”
“State and local governments have become more aware of and are utilizing trenchless rehab methods for repairing their aging and deteriorated culverts and drainage systems,” says Stephen Boggess, director, Snap-Tite Culvert Lining Division at ISCO Industries. “However, most are just ‘scratching the surface’ when it comes to proactively addressing these issues. We’ve seen an increase in asset management plans that include culverts and drainage structures. Tracking the condition of your culverts is the key to getting ahead of the problem. Great strides have been made the last few years but we have a long way to go.”
Culverts are primarily made out of corrugated metal pipe (CMP) or reinforced concrete, but brick and stone can be found in some of the older ones. Some of the newer culverts are made out of PVC, HDPE or galvanized metal. Their shapes and sizes are equally diverse. Shapes of culverts include elliptical, flat-bottomed, pear-shaped and box-like constructions, with single or multiple barrels, depending on the need. Their sizes are typically no smaller than 24 in. in diameter, with most ranging 48 to 72 in. in diameter.
The overall condition of the some 4 million miles of culverts in the United States varies, with those constructed of concrete seemingly in better shape than those of corrugated metal. There are some culverts reaching 100 years in age but those that are candidates for renewal are usually in the 30- to 70-year range.
General consensus of our culvert panel is that the culverts and drainage structures are in critical need of rehabilitation as they have outlived their intended lifecycle — yet they are still in use. The average age of these structures, according to our experts, is between 30 and 50 years, with some older than that. Corrosion is at the top of the list of problems associated with culverts made of corrugated metal, with the corrosion occurring on the bottom invert, virtually disintegrating it and necessitating a new bottom of the pipe.
“Some of the most common issues include rusted or failed culvert bottoms, corrosion and joint separation. These occur because of age, usage and simply the conditions around these pipes,” says Sekisui Western Regional sales manager Jacquie Jaques.
“Culvert problems vary throughout our country. As urban growth continues hydraulic capacity needs to be evaluated on a continual basis,” says Contech Engineering Solutions vice president of pipe promotion and distribution Wayne D. Peterson. “Abrasion and corrosion issues that ultimately lead to structural integrity degradation is an ongoing concern that requires agencies to constantly review current infrastructure needs.”
He adds that plastic materials require agencies to look at stress cracking that can also lead to structural and hydraulic issues. “Ultraviolet degradation becomes an ongoing concern with aged plastic culverts, too,” Peterson says.
The Role of Trenchless
Trenchless technology has been the go-to method for water and sewer pipelines for more than 40 years. The same cannot be said for culverts but the tide is slowly and steadily turning in this direction as more and more owners are applying trenchless technologies to its culvert and drainage structure work. Among the trenchless options for rehabilitation are sliplining, pipe bursting, cured-in-place (CIP) lining, shotcrete and grout-in-place (GIP); on the new installation side, options include pipe jacking, directional drilling, microtunneling, pipe ramming and tunneling.
“When direct bury is not cost-effective or site conducive, trenchless technology is the go-to option. Trenchless technology methods and options are site dependent,” says Peterson.
Lancaster notes that the two most utilized trenchless applications for culvert repair are CIPP and sliplining, with geopolymers and other spray-applied technologies gaining momentum. “Both CIPP and sliplining have a proven track record in this type of system in addition to well documented testing related to their lifespan as a fully structural system, which is important when the host pipe has reached its useful life,” he says. “Over the last five years, additional trenchless products and process, like geopolymers and other spray-applied techniques, have begun to be utilized more often in cases where relining is needed but the structural conditions of the host pipe are not nearly as severe.”
To determine which trenchless application works best for your project, Boggess suggests consulting the guidelines provided by American Association of State Highway and Transportation Officials (AASHTO). “AASHTO approved methods and products have been approved by DOTs in all 50 states and an AASHTO approval immediately signifies that that the solution has proven itself over the years,” he says. “Any repair method and applicable product should, at a minimum, have an ASTM that allows for the designer to establish a proper assumption base for design thicknesses and final material selection. Designers always need to consider the condition of the host culvert of structure before applying these equations to the final design.”
When determining how to proceed with rehabbing a culvert, there are several considerations to look at, such as hydraulics and structural requirements and issues. “This is especially true in corrugated metal pipelines as they tend to ovalize and collapse over time due to improper bedding during the initial installation, as well as shifting soils and dynamic loading from above ground traffic conditions,” says Lancaster. “On the other hand, it’s rare to find structural concerns in concrete host pipes, due to the construction of this material. In these cases, join infiltration, which can bring migrating soils and other media, tends to be the biggest issue which can cause less major road problem (i.e. sinkholes, depressions, etc.).”
Infrastructure projects are all about need and prioritizing those needs. Owners and municipalities have a limited number of funds to spend on projects each year and the list of infrastructure needs continues to grow. So, yes, money is always a key issue for culvert and drainage structure work, as any other infrastructure work. But there are other issues.
“The challenge for state DOTs is typically funding. Each state funds highway and infrastructure projects differently,” says Jaques. “Another challenge includes the various regional environmental concerns. The state has many ecological considerations when rehabilitating culverts. These include fish passage, wildlife protection and sensitive environments.”
Boggess also stresses the need for culvert inspections, which are a key part in determining which structures require immediate attention. “Proper inspection, identifying the problems and making proactive repairs is a major issue that needs to improve. Government agencies have made strides in improving these areas but we still have a long way to go,” he says.
But funding remains at the forefront of issues culvert repairs face — now and in the future. Our panel is clear on that aspect of this growing trenchless market segment.
“[Culverts are] a significant, though overlooked market that will require billions of dollars in infrastructure investment to meet federal and state requirements,” says Jaques.
“The greatest benefits of rehabilitation of culverts via trenchless technologies are extensive,” Boggess says. “The ability to minimize the impact in the community, work in a safe work space, funding, environmental impacts, other surrounding utilities proves as just the ‘tip of the iceberg’ for benefits with trenchless solutions.
“Culverts and/or storm sewers are synonymous to roads,” Peterson says. “If an agency has a road within their jurisdiction, they eventually will have a need for trenchless technology. The market is vast and involves every county within the United States, private and public entities.”
“As the state DOTs continue to gather funding in order to improve roadway surfaces, due to the ever-growing population, storm water pipelines and culverts will continue to gain more attention,” Lancaster says. “In order to continue to grow this market, our industry needs to continue to educate and market the wonderful advantages of the trenchless industry in the storm water pipeline and culvert market.”