SSC Underground Utilizes Trenchless Technology On Job

PHOENIX from page 1

The tunnelling portion of the job came to $4.3 million.

SSC Underground was tasked with using trenchless technology to burrow through the earth, allowing traffic and everyday life to continue overhead with minimum interruptions. This approach used small skid steers to dig through the rocks and dirt. Workers then used jackand-bore equipment to push the steel casing into the newly created hole. In the Sundt project, the enormous casings were 10-ft. long and 86 in. in diameter, tall enough that the entire Phoenix Suns professional basketball team could walk through without having to stoop.

Once the tunnel construction began, precision digging was required. On the Sundt section of the job, the workers needed to dig a tunnel so that the casings would connect the pipe being laid by Sundt in open-cut trenches with approximately 1-in. tolerance.

SSC Underground began working on the project in 2019 and wrapped it up at the end of 2022. SSC’s consulting division worked closely with design engineers and other contractors to devise an underground road map for the work. Using its underground potholing fleet, the crew located existing utility lines so that they could be relocated or pipeline alignment could be designed around them.

“Every dollar spent on pre-construction potholing/SUE saves $7.82 in construction costs,” said Arvid Veidmark, president of SSC. “Often when tunnelling, we will find previously unknown infrastructure, even gas lines, which of course can be quite dangerous.”

The tunnel crew installed the steel casings underneath major arterial roadways and intersections, neighborhood streets and an active water treatment plants. Ground conditions ranged from caliche, cemented cobbles, alluvium and hard dirt. Each day seemed to bring its own set of challenges as workers changed strategy to fit the soil requirements. The job required more than 12 trenchless installations. Workers managed each operation to minimize disruption to the public while considering time, cost and risk.

SSC kicked off the tunnelling with a 105-ft. installation of 66-in. casing for a 48-in. waterline under Glendale Avenue at the base of Piestewa Peak Mountain, using a motorized boring unit from Robbins to perform this crossing as the ground was solid rock. Working for Kiewit, this crossing was a key connection as this section ran through neighborhoods and had a major impact to residents.

The second segment included six 86-in. diameter tunnels under intersections along the 32nd Street alignment for a total of 834 ft. for a 66-in. waterline. These tunnels were constructed using an S70 Bobcat skid steer equipped with either a hammer attachment or a rotary head to do the digging in hard dirt conditions. Production varied between 3 ft. to 9 ft. of installation per shift. As a subcontractor to Sundt Construction, SSC worked as a partner to sequence the tunnels to minimize traffic lane closures and keep access as open as possible to the many businesses along this corridor.