Everett Litton, Vice President and National Practice Lead for Trenchless Technology at WSP USA, discusses the upsides of using trenchless technology construction
By Everett Litton, PE
I firmly believe that we should all be good stewards of the environment. Additionally, it’s important to also recognize that infrastructure and their continual improvement is critical to society and our way of life.
That’s precisely what excites me about the trenchless technology industry: it allows us to construct necessary infrastructure while minimally impacting our communities and the environment. These technologies allow us to cross sensitive areas with minimal to no impact on the environment, and when done properly, are both extremely meaningful and beneficial for our society.
Future Ready with Less Disruption
Trenchless technology is a series of construction techniques used to install or rehabilitate underground infrastructure – primarily pipelines and underground utilities – with minimal disruption to surface traffic, businesses, residents, and the environment.
This technology offers numerous benefits for both clients and communities. It minimizes disturbances to the existing environment, as well as traffic impacts and contributes to less disruption in congested urban areas. It also reduces the need for new space underground and problems associated with pipeline routing; requires less overall space underground, which minimizes the chances of interfering with existing utilities or abandoned pipes; requires less exposed work area and is therefore safer for workers, communities, and the environment; significantly reduces the need for excess spoil removal; and minimizes damage to pavement and disturbances to other utilities.
Trenchless Technology inherently supports WSP’s Future Ready® principles, as the methods of installation are resilient and environmentally sensitive, and often help to reduce the carbon footprint of the construction project by minimizing impact and reducing spoil removal, while also being capable of dealing with a wide range of constraints and challenges.
WSP recently used trenchless technology to help Indiana and North Carolina construct their first curved microtunnel projects. Microtunneling includes the use of remotely controlled microtunnel boring machines, which are commonly used to install pipelines less than 96 inches in diameter, and usually too small for manned tunneling operation. While using trenchless technology for these projects is not uncommon, curved microtunneling is relatively new within North America and poses greater difficulties that we are now able to overcome.
The first curved microtunnel in Indiana — was the State Road 37 (SR37) Improvements Project — included years of collaboration between the cities of Fishers and Noblesville, Hamilton County and the Indiana Department of Transportation. This led to a concentrated effort to address traffic congestion and public safety challenges along SR37 in Hamilton County.
The at-grade intersections at 126th, 131st, 141st, and 146th Streets were redesigned as underpasses to allow for the free flow of traffic on SR37. For this project, WSP was selected to design two offsite gravity drainage storm sewers to carry drainage from the depressed underpasses to natural water bodies, and trenchless construction methods were chosen to provide drainage for the newly depressed interchanges.
Gravity outfall sewers were selected instead of pump stations, which eliminated long-term operation and maintenance costs. Two drainage outfall storm sewers were designed and successfully constructed, at inverts of 17 to 44 feet below grade, to carry roadway drainage westward to its natural surface water bodies, Shoemaker Ditch, and the White River.
The SR37 project used two trenchless construction methods: two-pass tunneling and microtunneling for installation of the 54-inch diameter storm sewers. The project included the installation of 6,500 feet of storm sewer, which successfully navigated difficult ground and groundwater conditions for the existing 2,650-foot-long south drainage line and the 4,700-foot long north drainage line.
Trenchless success was achieved in this project by overcoming boulders and groundwater conditions, and successfully installing a record-breaking 2,304-foot long curved microtunnel. The project won Trenchless Technology magazine’s 2020 Project of the Year, New Installations Honorable Mention, and the American Council of Engineering Companies’ 2021 Indiana Engineering Excellence Honor Award.
Similarly, in North Carolina, WSP served as engineer-of-record working with Charlotte Water for several one-pass sanitary sewer tunnels. The 3,592-foot-long by 48-inch diameter reinforced concrete utility pipe was installed using a Herrenknecht AVN-1200 microtunnel boring machine, within variable subsurface conditions that consisted of granitic rock with strengths up to 30,000 pounds per square inch, as well as soft alluvial deposits. Construction is ongoing and included an already complete 1,155-foot-long curved microtunnel, which was the first planned direct jack curved sanitary sewer in North Carolina.
Trenchless technology projects are less impactful to the community as compared to open-cut construction projects. Many communities already require trenchless construction as a normal practice, and the technology is being adopted in others, albeit at a slower rate.
Contributing to that slower rate in some communities is an impression that trenchless technology is more expensive than open-cut construction, requiring specialty contractors to perform the work. At small diameters the installation cost is actually quite similar to open-cut installation, but only becomes more costly on a per-foot basis at larger diameters.
And when the full social costs are considered, such as community and environmental costs, trenchless technologies are often less impactful and competitive — if not more favorable — than open-cut installation methods. There are also significant advantages to both cost and schedule, mostly from permitting efficiencies, when using trenchless technologies for crossing wetlands, roadways, railroad tracks, streams, rivers, and other obstacles or sensitive environmental areas.
We are witnessing continual advancement of trenchless technologies based on our experience and innovations developed through previous project successes, which leads to continuous improvements and efficiencies within the industry. Tooling developments are allowing for excavation in a wider variety of geologic conditions, methods are being refined for longer lengths, and longer reaches and more adaptive tooling continue to reduce the impacts of trenchless technology by reducing the areas disturbed at the surface, along with the carbon expended on each project.
Today, when the full spectrum of costs and potential community and economic impacts are considered for the life span of a project, trenchless technology installations are emerging as the most viable and practical option for pipeline projects throughout North America and worldwide.
WSP’s capabilities related to trenchless technology include planning, program management, risk management, detailed design and onsite services during construction, resulting in an in-depth understanding of local geology, ground-structure interaction and construction technologies, combined with the systematic application of investigative, scientific, engineering and risk management techniques for multiple trenchless projects.
WSP can point to continuous growth and expansion in tunneling technology, from its earliest roots in the US, more than 130 years ago, to its vast international presence today. The firm’s work in the late 1800s includes substantial design and construction of the first New York City Subway.
That heritage in tunneling continues to this day and WSP is proud of the advances it is making using modern trenchless technology techniques to assist clients and owners.