C+S March 2023 Vol. 9 Issue 3 (web)

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 drain - age 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, Shoe - maker 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 En - gineering Excellence Honor Award.

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 installa- tion 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 previ - ous 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 adap - tive 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. Trenchless Offerings 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 tech- nologies, 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 tech- niques to assist clients and owners.

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 mi - crotunnel 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 microtun - nel, which was the first planned direct jack curved sanitary sewer in North Carolina. Considering Cost 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 impres - sion that trenchless technology is more expensive than open-cut


March 2023 csengineermag.com

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