DPR Utilizes Industrial Fabric to Stabilize Soil for Willamette Industries’ Manufacturing Facility in Arizona

Before footings could be laid for a 225,000-sq.-ft. manufacturing and distribution plant in Tolleson, Ariz., DPR had to decide between three options for stabilizing the soil—lime stabilization, over-excavation, or the installation of a woven fabric, known as Mirafi.

For more than a century, the 5.2-acre site had been heavily irrigated for growing cotton, making it wet and unstable, so DPR investigated its options. “Lime stabilization and overexcavating were both too expensive and too time consuming,” said DPR Project Manager Brent Banning. “The Mirafi solution made the most sense, it was economical and allowed us to monitor a test area before installing it.” DPR excavated a test point and tracked the area’s movement. After two weeks the soil had not moved, so crews proceeded to stabilize the soil with the fabric, overlapping work on the north and south halves of the building’s footprint.

Mirafi’s origins date back to 1953 in Holland where tough industrial textiles are used to reinforce and retain dikes. In the 1960s, a North Carolina firm developed and took its name from an experimental fabric known as Miracle Fibers. In 1991 the Dutch company and Mirafi joined forces and, as part of the Royal Ten Cate, is known as TC Mirafi.

Mirafi helps distribute soil load while allowing water to percolate through, similar to putting plywood over mud. To build up the soil’s bearing capacity, DPR crews excavated five feet of native soil below subgrade and reinstalled the soil in lifts—installed wet soil, compacted it, and added more soil—back to subgrade. The subgrade then was proof-rolled using a water truck, one or two layers of the Mirafi were installed by Ricor, Inc., and the task completed by putting in three feet of imported soil lifts on top of the fabric.

By using this method, Banning says DPR saved the owner, Willamette Industries, six to eight weeks on the schedule and was able to complete the project within the tight nine-month schedule.