Culverts and storm sewers have been a part of our infrastructure even before the advent of the federal highway system in the 1940s and 1950s, when the demand and the necessity for drainage pipes sprang from the growth in the number of automobiles traveling the roadways.
Culverts and storm sewers today are an important facet of an infrastructure, allowing water to flow under roadways, railroads, trails or any other obstruction. Larger size ones are labeled by many Departments of Transportation (DOTs) as “bridges” in their official paper work as culverts may be used as bridge-like structures to carry traffic across waterways.
A vital part of the infrastructure, these structures are need of attention as they continue to age and deteriorate. Slow to realize the benefits of trenchless technology, owners are now turning to it to install new culverts or rehabilitate the ones that can be saved.
Trenchless technology has been a part of pipe renewal and replacement for more than 40 years as municipalities and utility owners faced with federal mandates and consent orders to fix their water and sewer lines. But culverts were a different story and were virtually ignored as their sanitary sewer and water brethren were looked after.
But over the last 10 years, the trenchless industry has seen an influx of culvert and storm sewer work — a growth area for an industry continually expanding its reach.
Using trenchless technology to address the aging and deteriorating culvert and storm sewer market has been described by industry insiders as a natural extension for the cost-effective and minimally invasive rehabilitation and construction industry that has proven itself over and over through its growing soaring acceptance.
Trenchless technology is now at the forefront of rehabilitating our country’s underground infrastructure, in particular the sanitary sewers. Using the gamut of rehab trenchless methods, municipalities, owners, engineers and contractors know and accept the benefits of these methods, which makes the move into culvert acceptance much smoother.
“I believe it to be an untapped market for trenchless technology,” says Dr. Mohammad Najafi, professor and director of the Center for Underground Infrastructure Research and Education (CUIRE) at the University of Texas at Arlington. “And in most cases, trenchless may be the only solution to address [culverts and storm sewer]repair, replacement or rehab needs. The only other alternative is to dig the roads, which would generate traffic disruption and safety issues. The [state]Departments of Transportation don’t want to do that. Trenchless is the only solution.”
“Essentially I think it is under-utilized,” says Insituform Technologies senior applications manager Lynn Osborn. “Although culvert rehabilitation has occurred for years, it’s starting to catch on. Storm water and culvert issues were really put on the backburner for the last 20 to 30 years” as attention was given to the water and sanitary sewer lines.
“People are discovering other sectors of our infrastructure that need attention,” he says.
Following highly publicized infrastructure disasters, such as the collapse of a Minnesota bridge in 2007, regulatory agencies have cracked down and begun requiring mandatory annual inspections on structures, including culverts, in recent years. Getting a good look at their condition, DOTs can no longer put aside these projects but instead assess and address them.
Trenchless professionals such as Najafi have worked directly with some DOTs in studying and finding solutions to culvert conditions. Najafi worked with the Missouri DOT in 2002-2003, Michigan DOT in 2004-2005, the Midwest Regional University Transportation Center in 2006-2008 and Texas DOT in 2010-2014 on such projects. The Trenchless Technology Center (TTC) was authorized in 2008 by National Cooperative Highway Research Program to study culvert rehabilitation to maximize service life while minimizing the costs and traffic disruption. The researchers are tasked with developing the design methodology, or methodologies, for the trenchless renewal of culvert pipes that will ultimately find its way into AASHTO’s LRFD Bridge Design Specifications.
“The invisible critical components of culverts have been neglected,” Najafi says. “The location and condition of these pipes comes to notice only when there is a problem such as settlement or complete failure of a roadway. The deterioration of culvert pipes and other components is a growing problem for transportation agencies. Their deterioration, because of their increasing age or change of service conditions such as increasing flow due to changing watershed conditions is increasing the wear and tear of these pipes. Additionally, higher service loads and corrosion are other major issues.”
Trenchless technology has come a long way from its early days when manufacturers had to “sell” municipalities, owners and engineers on its potential and benefits. Around the country, now the no-dig techniques for rehab and new installation are widely accepted and, in many cases, are now the first options for repair of underground infrastructure. The technology’s proven track record and capabilities are well documented.
Methods for Culverts
Trenchless technology offers culverts and storm sewers a multitude of options when it comes to the structural rehabilitation of existing structures and the construction of new ones. Closing down highways, diverting and delaying traffic and digging up the earth are not attractive in the eyes of DOTs, so the minimally-invasive trenchless methods have come to the forefront of available choices as they map out their construction plans.
Culverts are primarily made out of corrugated metal pipe (CMP) or reinforced concrete, but brick and stone can be found in some of the much 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 barrels 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. Corrosion is the No. 1 problem for culverts made of corrugated metal, with the corrosion occurring on the bottom invert, virtually disintegrating it and necessitating a new bottom of the pipe.
So which trenchless methods work best on these structures? Cured-in-place pipe (CIPP), spiral wound, spray-on cementitious or polymers, sliplining, fold-and-form, shotcrete and grout-in-place are among the methods that avail themselves to rehabbing culverts. On the new installation side, pipe jacking, microtunneling, pipe ramming and tunneling are pretty common techniques used to replace the ailing structures.
“All of the methods can perform well,” says Osborn, noting that there are design issues for each method and each type of culvert. Osborn has been with Insituform for more than 30 years and spent nine years prior to that as a consultant in the water and wastewater industry. He says that culvert work has been a part of Insituform’s repertoire since the mid-1980s, just not one that has seen significant growth and interest until the last 10 years.
Sliplining culverts was successfully used by DOTs long before trenchless technology was a recognized industry; however, this method has one significant drawback that limits its use — diameter reduction. “The problem with this technique is that you give up so much hydraulic capacity. When it comes to culverts, anytime you give away hydraulic capacity that’s a negative,” explains independent trenchless technology consultant Ed Kampbell, owner of Rehabilitation Resource Solutions, Columbus, Ohio, and longtime trenchless technology professional. “As a general rule, the more an area develops, the more [water]runoff you have. Therefore, [DOTs] are very reluctant to give up any hydraulic capacity. The options early on weren’t that good.”
Najafi says that use of CIPP has the highest potential of trenchless methods due to its diverse application of water, steam, heat and UV, and, most importantly, the pipe’s diameter is not significantly reduced. “CIPP can enhance structural capacity and at the same time it doesn’t reduce the diameter of the pipe,” he says. “It can actually improve the pipe flow capacity because it will be smoother than what the existing pipe was.”
Handling culverts and storm sewers through trenchless produces an entirely different set of challenges for contractors, manufacturers and design engineers to ensure the structure fully rehabilitated. As stated above, culverts are not all round, as are most sanitary sewers, but come in a multitude of shapes, which make the traditional CIPP application, for instance, a bit trickier to make sure the CIPP liner fills every nook in it — i.e. having a round peg fit in a square hole. Culvert work is also done in remote and hard-to-reach locations of short shots usually no more than 150 ft in length, making cost a factor in setup, location and application.
Cost seems to have a determining factor early on. “For a contractor, no matter what system you are using, you are setting up in a location and mobilizing and demobilizing. It doesn’t matter if it is 50 ft or 1,500 ft. It still costs you to set up and you may have a series of culverts to do. Costs you to move from one to the other. Short ones are actually more expensive per unit price per linear foot than the same size in a long run,” says Mike Spero, president of Danby LLC Kampbell concurs. “The real cost for CIPP, which is the setup, is spread out in sanitary sewers and it isn’t in culverts because they are much shorter segments,” he says. “That and the remote access of culverts, makes bringing materials, including water, to the site that much more expensive.”
But it appears that owners are now seriously factoring in the costs outside the actual rehab of the pipe, such as disruption to traffic and the public, as well as landscaping costs. Also, the evolution of the technology and products that the trenchless industry offers has made these options even more attractive to the owners paying the tab.
Spero offers another difference in rehabbing culverts vs. sanitary sewers — what they find inside the pipe. “It’s not as nasty to work in culverts as it in sanitary sewers. You don’t have to deal with the bacteriological slime, organic sediment or hazardous waste; however, you do have different issues such as snakes for one,” he says. “One time we discovered a 6-ft alligator on the job. We had cleaned out the pipe and came back the next day to line it. Our guy crawled in and came right back out, saying they had a problem!”
As the culvert market started to grow, trenchless companies began offering more technology and products to cater to that need. Insituform had been working with state DOTs since the mid-1980s but it wasn’t until 2002 that it developed its own CIPP process for the culvert market, which uses steam as the heat source for curing. “What we have learned is that when you rehab culverts with our standard water inversion method, you at times have to truck water in and once the CIPP is cured, you have truck it away. With steam, there is just less water to deal with,” Osborn says.
Osborn refers to Insituform’s CIPP process for culverts as the “DOT Method,” which involves not inverting the full tube, which takes a lot of laydown space for materials and equipment. The tube is wetout off site and brought to the jobsite and pulled in, where it is inflated and steam cured.
Kampbell says there are a plethora of technologies available and one of the trenchless methods he is keen on these days is the use of centrifugally cast-in-place cementitious liners, such as Permaform’s CentriPipe system, which is designed for corrosion protection and complete structural renewal of storm and sanitary sewer pipe between 30 to 120 in. in diameter. “Unlike shotcrete, which DOTs are familiar with using a nozzle man standing in the pipe and spraying it on the pipe’s walls, now [the industry]has mechanized robots that precisely place the material against the periphery of the host pipe at a much greater velocity with minimal rebound, which gives them a more densely packed cementitious mortar lining,” Kampbell says.
Danby LLC has a grouted-in-place lining (GIPL) method that it has been using in North America for more than 25 years. Spero says it is a structural lining method that uses a PVC liner to provide a water-resistant and corrosion-resistant interior shell. The annular space between the pipe and liner is filled with high-strength grout.
“[Manufacturers] have tweaked their products and technologies so they can be used for culvert and storm sewer applications,” Najafi says. “This is a huge and untapped market.”
The trenchless industry likes the potential of the market segment and sees sustainable growth in the coming years, although acknowledging that it will not reach the percentage of the sanitary sewer market. “It’s a segment we definitely keep our eyes on,” Osborn says. “It’s a good segment, not a huge one. It is definitely a niche market.”
What makes trenchless an easier sell to culvert and storm sewer owners is the overwhelming acceptance of trenchless applications in the sanitary sewer market — they know the technology works. “The familiarization of the technology and techniques is key,” Spero says. “Because they have used the technology for sanitary sewer rehab for many, many years, engineers, are more familiar, as are the public and government officials.”
And money is always an issue, as it is with all underground infrastructure and culverts fall into that category. “Keep in mind that it has been and probably always will be that the politicians control the money and they will put the money where it is visible, like for roads, bridges and parks — where people can see where their tax dollars are going. They don’t like to put money underground because people can’t see it and especially with trenchless where you almost never see the work being done,” Spero says.
“The DOTs woke up a little later to the process of trenchless but they are trying to catch up and understand the value of it. They are getting there,” Kampbell says.
Sharon M. Bueno is managing editor of Trenchless Technology.