Pittsburgh’s South Side needed new pipes. During a rainstorm in the neighborhood, water poured through downspouts on many houses and buildings, off their properties onto the sidewalks and into the street. It pooled and froze creating dangerous icy sidewalks. Underground, the neighborhood has a combined sewer: wastewater from nearby homes and stormwater on the ground mix into the same pipe.
Pittsburgh Water, the city’s water agency responsible for those pipes, has been working on a solution to separate the sewer — with a dedicated storm sewer and a separate wastewater sewer. And, where they can, take those downspouts and plug them into the new storm sewer. The water that now spills onto the street would flow straight into a pipe. The South Side Flats Sewer Rehabilitation Project has been underway since last summer and construction is about halfway done.
But the recently completed work on Wharton Street looked a little different. Typically, a crew would dig a deep trench along the entire length of the street between 18th and 21st streets. The project was expected to take three months to complete. “But when we got towards the end of the design process preparing for construction, it was determined that that approach was not going to work,” said Mora McLaughlin, construction communications project manager at Pittsburgh Water.
Instead, they decided on an innovative approach called microtunneling.
Microtunneling is a way to install a pipe underground without having to dig a long trench and chew up an entire street for blocks. Instead, a remote-controlled boring machine digs through earth, sucks up the dirt and water and brings it back to the surface, while plugging in pipe in its wake as it tunnels away.
“It's perfect for an urbanized setup,” said Hiva Mahdavi, regional conveyance leader at Stantec, an international engineering firm. “It's perfect for a sensitive environment like river crossing. It's perfect for a rail crossing, highway crossing. It has so many safety features that kind of enable the contractor to install the pipe without really disturbing the neighborhood, without really disturbing the existing structure.”
Microtunneling begins with two deep shafts about a block-long. On Wharton Street, workers dug one near 18th street and one near 21st. A crane lowers the microtunnel boring machine into the starting shaft. On the surface, an operator navigates the machine remotely. This is a huge advantage, according to Mahdavi. “It means you don't need workers and personnel down the tunnel, which was kind of a safety issue.”
On the front of a machine is a cutting disk to grind through the soil that can be swapped out to cut through different types of soil, rock, or clay, Mahdavi said. After the machine is lowered, a hydraulic jacking system behind the machine starts jacking the machine into the ground. They pump fluid through the machine and the pressurized fluid takes the soil and water back up to the surface.
The crane lowers the pipe, connects it right behind the microtunnel machine, and the hydraulic jack expands, then pushes forward. And again. The hydraulic jack “stretches itself, pushes into the ground, and then retrieves back, next pipe comes down, next pipe connects to the pipe that is already installed, and pushes forward again,” Mahdavi said. It’s a cycle, one piece of pipe at a time, until the microtunnel boring machine peeks out at the bottom of the shaft on the receiving end and the pipe is installed.
On Wharton Street, the work took 11 days instead of the estimated three months by the traditional trench method. Microtunneling is more expensive, McLaughlin said, but in this case, a quicker installation and minimal disruption to locals made sense. Right now, Pittsburgh Water has no plans to use microtunneling on any other pipe installation projects.
“It's good we have this experience now,” McLaughlin said. “We know how, for example, how to set up the stabilization of the pits. We've worked with a contractor and we know the right questions to ask. So, I certainly imagine we'll always keep it in the back of our minds as a potential in the future.”
Work continues on other sewer repair projects throughout the South Side and is expected to wrap up by spring 2026.
