Digging deep
Poured-in-place parking deck built into UA hillside

By Mark Friedman

Before Baldwin & Shell Construction Co. of Little Rock could begin work on the $25 million nine-story concrete parking deck at the University of Arkansas at Fayetteville, it had to remove nearly 120,000 cu. yds. of dirt and rock from a hillside.

University officials wanted to preserve the panoramic views from the academic buildings, which meant the deck had to be built into the side of the hill, said Craig Curzon of Polk Stanley Rowland Curzon Porter Architects, the project architect.

The poured-in-place, 750,000-sq.-ft. parking deck - the largest in Arkansas - has 2,149 parking spaces and opened in late August.

"On the west end, you actually drive in off the street onto the sixth floor of the deck," said Ted Grumbine, a senior project manager for Baldwin & Shell. "On the east end, you drive in on (the first floor) and on the north side there's an entrance on the fourth and a second levels."

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"The deep excavation will help to maintain a lower profile, in respect for the Fayetteville-wide views of this important UA promontory," said Rick Hamilton, UA construction coordinator. "(The contractor and architect) have been tremendous in assisting layout and design to request the important aesthetic heritage of the UA."

The university's master plan called for several new parking areas on campus, said Gary Smith, the university's director of transit and parking.

"We could continue to build surface lots (but) here we can put a lot more parking in a condensed footprint, and it provides it relatively close to people's destinations," Smith said.

Because of the size of the structure, 385 ft. by 435 ft., the architect split the deck into two halves and created a 30-ft.-wide shaft between the two sections to allow light and air to reach the lower levels.

Before construction began on the deck, the contractor drilled 250, 36-in.-diameter retention piers on the three sides of the hill. The retention piers formed a retaining wall around the hill, keeping the dirt in place. The piers varied in length, but some were as long as six stories, Grumbine said.

To remove the dirt, Baldwin & Shell used controlled blasts, which marked the first time the university had allowed blasting on campus.

"Before we started blasting, there was a preblast survey done," and 1,200 photos were taken, Grumbine said. "We have a picture of every house, of every wall, of every structure within three blocks in any direction of (the parking deck) so that nobody could come in and say, 'You cracked my walls.'"

Next, the dirt, shell and a hard limestone strata were hauled from the hillside and a 3-ft.-thick, 60-ft.-tall, 120-ft.-long wall was erected in the hole, Grumbine said. Baldwin & Shell then began constructing the parking deck 60 ft. below grade.

"The foundation is nothing more than big pad footings" measuring about 15-ft. wide and 6-ft. thick, he added.

Using ready-mix concrete that was brought to the site premixed by a subcontractor, Baldwin & Shell poured the concrete into a form where post-tensioned cables were placed.

"Then we stressed these tendons and put the concrete in compression," Grumbine said. "That's what holds this whole mess together. The placement of these tendons is supercritical. After the concrete sets workers stripped the forms and reused them on the next floor."

The 6-in.-thick deck slabs required 4,000 psi concrete, and the 30-in.-diameter columns were 6,000 psi. The distance between the floors is 11 ft., 4 in.

Also, Arkansas Precast Corp. supplied more than 600 pieces of architectural stone and 230 pieces of precast for the deck.

To assist with the pours, Baldwin & Shell used a tower crane with a 270-ft.-long boom.

"We had to set it in one location, build two-thirds of the deck, move the crane and take the other third up," Grumbine added. "That's because we couldn't get a crane big enough to reach across all of it."

A limited laydown area made the timing of material deliveries critical.

"The site is so small we had to bring in the rebar and the post tensioning cable just a day or two before we needed them," Grumbine added. "We had no place to stockpile it."

The contractor coordinated with suppliers in Tulsa and San Antonio to ensure that shipments arrived on schedule. It also used a new testing method to monitor concrete maturing rates.

Baldwin & Shell implanted a sensor from intelliRock, which is sold by Engius of Stillwater, Okla., into the wet concrete. Using a handheld device, workers were able to monitor the strength of the concrete from the embedded sensor without having to ship a cylinder to a lab for testing.

The electronic test could be done several times a day - at virtually no cost - until the desired strength was reached, Grumbine said.

"That allowed us to get the forms off and moved up faster, and time is money," he added. "Usually you would wait three days before you break a slab. We reached 75 percent in as little as 30 hours on some of our pours."

A two-story transit facility and bus stop are included in the parking deck.

"The original plan called for the bus pullout lane to have been a bridge structure from the ground over to the deck," Grumbine said. "The university decided it didn't want it as a bridge structure, so we had to build (the 60-ft.-tall) wall so we could put fill behind it."