In early 2024, a 91-metre (300 ft) long and 1.2-metre (48”) diameter underground gas pipeline was installed beneath the most congested highway in the United States, the Cross Bronx Expressway in New York City. This east-west running highway is notorious for its slow-moving traffic that doesn’t stop even at nighttime.
When energy company Con Edison decided to upgrade the original 11-kilometre (7-mile) long north-south running gas pipeline built in 1948, one of the biggest challenges for bringing it up to modern standards was how to get over – or in this case, under – the Cross Bronx Expressway. The city of New York could not afford any disruptions on this critical road.
Underground Surprises
The initial plan was to use micro-tunneling technology for the pipeline installation. However, during the excavation of the launching and receiving shafts, it became apparent that the ground was more challenging than the geological information had indicated: large boulders, fractured ledge rock, and dense soils were found. Micro-tunneling is best suited for soft ground like sand or clay, so these findings posed significant challenges to the geotechnical engineers.
Luckily, the solution was not far away. New York-based horizontal drilling company Bortech Inc proposed to Con Edison the use of a DTH method, a percussive hammer powered by pressurized air. The key feature of the proposal was that Bortech uses Mincon’s hammers, shock absorbers, and casing systems equipped with Spiral Flush air control technology, which is crucial in urban DTH drilling.
The great advantage of trenchless methods is that they allow for the construction of infrastructure under existing roads without causing major disruptions to traffic. This saves time, money and the city dwellers’ nerves. Furthermore, Mincon’s tools offer advantages when compared to micro-tunneling: they are effective in all types of ground conditions, including rocky terrain. Another benefit is reliable air control, which makes air drilling possible even in complex situations.
DTH Drilling Needs Air Control
Mincon’s patented Spiral Flush air control technology is needed to prevent over-drilling when the pressurized air flushes the cuttings away from the drill hole. The excessive removal of soil would quickly lead to ground subsidence, something that would be catastrophic under a busy street where people and goods need to move around the clock.
Spiral Flush works by avoiding the discharge of high-pressure air directly into the ground. Instead, the pilot bit is designed to direct the airflow and the cuttings back into the casing. In addition to this safety-increasing feature, the drilling efficiency and fast penetration rates come from the fact that the air-powered hammer, together with the pilot bit, effortlessly crush the rock of any hardness while maintaining the directional stability.
Time to Prove
But let’s come back to New York. The Con Edison project, where CAC Industries Inc was the main contractor, was the first ever utility tunnel in New York City that was drilled with DTH hammer technology. This meant there were high expectations placed on the method, tools and the people doing the work.
Finally, in late March, when Mincon’s horizontal casing system saw daylight again on the other side of the Cross Bronx Expressway, the project could be called a success. Drilling went as planned, without interruptions to the traffic, neighboring structures, or surrounding ground. After the drilling phase, the actual gas line was installed inside the strong steel casing.
The president of Bortech’s trenchless division, Robert Titanic, commented on their experience: “We have been very pleased with the performance and the peace of mind that Mincon tool has given us, especially with their Spiral Flush air technology.”
We have been very pleased with the performance and the peace of mind that Mincon tool has given us.
— Robert Titanic, Bortech Inc.
This project serves as an excellent demonstration that air-powered DTH hammers can be used in tight urban environments, as long as air control is taken care of, and the constructor is experienced enough with the method. Contact your local Mincon expert to learn more about Mincon’s drilling solutions and Spiral Flush air control technology.
Also, watch the video below, to see more details about the different drilling steps and the tools used in the project.
Learn more about Mincon’s horizontal casing system HERE.
Learn more about Spiral Flush air control technology HERE.
