Google Fiber, an Alphabet division that is entering the internet service provider (ISP) market, relies on a special fiber installation technique to be competitive with existing ISPs: shallow trenching. Shallow trenches are much faster to construct than traditional methods of fiber installation, such as mounting cables on utility poles or digging deep trenches. They minimize site disruption and accommodate multiple conduits for fiber. Use of shallow trenches has enabled Google to roll out its broadband service very quickly in several cities.
When fiber was being laid in Salt Lake City, micro-trenches measuring 2 in. wide by 9 in. deep—a common dimension for micro-trenches—were cut into pavement on various roadways, both municipal roads and those overseen by the Utah Department of Transportation (UDOT). After conduit was laid, the trenches required backfilling. However, the 2-in.-wide trenches were too narrow to easily backfill with concrete, which often has aggregates measuring 1 in. in diameter and could have resulted in unfilled areas in the trench.
The solution was Rapid Set® Flowable Fill, a high-performance backfill where Rapid Set® cement is mixed on the jobsite with aggregate and water. Sixty cu. yds. of Flowable Fill (4 tons of Rapid Set cement) were used, mixed with a volumetric mixer and requiring no finishing or curing.
Salt Lake City’s micro-trenching work occurred between Feb. 12, 2020 and March 2, 2020, when Utah was still experiencing winter weather. Not only did Flowable Fill flow well into the trench’s small space, but it set up quickly despite the cold weather, achieving the specified flexural strength requirement of 500 psi in 28 days, with half the maximum strength at opening, which was a few hours. Achieving the specified opening time to traffic would not have been possible with conventional portland cement flowable fill because of the severe winter temperatures.