WATCH: What exactly is that giant black mound along I-5 in Tacoma?
My 7-year-old son calls it the Great Wall of Washington.
It’s that huge black rampart rising on the north shore of the Puyallup River near where Interstate 5 crosses in Tacoma.
Drivers can’t miss it, whether they’re headed north out of Tacoma or south into the City of Destiny.
So what the heck is it, anyway?
Neal Uhlmeyer, a project engineer for the state Department of Transportation, dished the dirt last week.
It is an earthen abutment for the new bridge that will carry northbound I-5 traffic across the river, Uhlmeyer said.
“It will create a smooth profile to tie the bridge back into I-5 on the north side of the river,” he said.
It will create a smooth profile to tie the bridge back into I-5 on the north side of the river
Neal Uhlmeyer, DOT project engineer
Crews hired by the Transportation Department have been working on the bridge for more than two years and hope to have it open to traffic by fall 2017.
The work is part of two projects on I-5 between South M Street and Port of Tacoma Road that will pave the way for carpool lanes eventually to be extended from Fife through Tacoma.
Nine of 10 concrete piers that will take the interstate across the river on the new bridge have been constructed, Uhlmeyer said, and workers have begun installing the more than 120 girders needed for road bed.
“Those will just keep marching across the valley,” he said.
And they’ve been building that big berm.
For six months, a steady stream of dump trucks towing trailers called “pups” have been unloading dirt onto the pile.
Uhlmeyer said the abutment will hold about 270,000 cubic yards of material when finished. That’s about 11,800 truck-and-pup loads, he said.
270,000 Cubic yards of material needed to build the abutment
The highest part of the wall will reach 45 feet.
The black coloring comes from large synthetic bags and industrial-strength plastic mesh workers are using to complete the outside of the abutment. The system, which stretches from 10 to 40 feet into the wall’s structure, reinforces the soil.
Eventually, a concrete fascia wall will be poured to cover up that system, Uhlmeyer said.
He said the fascia wall will have a “random board finish,” which a Transportation Department manual describes as “natural looking, rough-cut wood textures.”
The dirt is coming from a variety of places, the majority from local borrow pits, Uhlmeyer said.
“They’re happy to sell it to us,” he said.
So why not just build more concrete piers instead of moving all that dirt?
As with most things, it comes down to money.
The abutment is much more inexpensive to build and maintain than additional piers, Uhlmeyer said.
Drivers can expect to see construction on the great wall continue for several more months, he added.