SBJ/June 4 - 10, 2001/No Topic Name

Cards’ stadium on solid ground

Imagine a football stadium supported by 700 concrete stilts built on the side of a mountain, and you've conjured up a picture of the foundation needed for the Arizona Cardinals' new home in Tempe.

The 73,000-seat stadium is so large and has so many parts to it that "it's like building a small city," according to one environmental consultant.

For this project, the "stilts" actually are 700 reinforced concrete columns reaching deep underground, and the "mountain" is the sloping bedrock under the soil.

Some columns could go as deep as 45 feet before hitting rock. Those will be at the south end of the structure. At the north end, the columns will be shorter because the bedrock is closer to the soil surface.

Those are some of the details in a report Tempe-based Geotechnical and Environmental Consultants Inc. is preparing for Hunt Construction Group. The report should be ready in the coming weeks, GEC principal Donald Spadola said.

The $334 million stadium and multipurpose facility is planned for 60 acres at the southeast corner of Washington Street and Priest Drive. In recent weeks, GEC crews drilled in several places on the property to determine the depth of the bedrock and to obtain rock samples, as well as confirm the level of the groundwater table.

"We will drill down into the rock, and we will socket [the columns] into the rock 10 to 15 feet," Hunt contracts manager Dennis Gilbert said. "What that does is put the load on rock throughout the whole facility."

GEC senior project manager Tim Anderson said loads will vary from 200,000 pounds on the smallest columns to 5 million pounds on the largest.

"The whole stadium is going to be supported by bedrock," he said. "There is no better material to build a stadium on."

The rock core samples obtained by GEC were subjected to pressure tests at the company's laboratory. The tests showed that the rock "is as strong or stronger than concrete," Anderson said.

Spadola said the Tempe site, while challenging because of the slope as well as the angled bedrock, has its advantages. One is the relatively short distance to reach the rock. In the West Valley, where developer John F. Long offered to donate land for the stadium, it could be 80 feet or more from the surface to solid rock, Anderson said.

Once holes are drilled for the concrete columns, the holes will be lined with steel casings to keep out ground water, sand and gravel while concrete for the columns is poured.

Spadola added that since the stadium is under the flight pattern to Phoenix Sky Harbor International Airport, the north end of the site will be excavated enough to keep the stadium under the Federal Aviation Administration's 200-foot height limit.

A unique feature of the stadium is that its field will be mounted on rails. The football field will be rolled out of the stadium on a huge structure so the stadium can accommodate concerts, conventions and other activities. Electric motors will move the field back and forth, and hydraulic systems will help start and stop it.

CMX Group Inc. is helping design the retractable field. It will be sod and an irrigation system on a mammoth concrete tray. The field, weighing an estimated 14 million pounds, will remain outside the stadium most of the time to expose the grass to sunlight. Each game day, the 240-foot by 360-foot field will be wheeled back inside the stadium, Spadola said.

One analyst said Hunt and its subcontractors will employ 1,000 workers during construction. Work is to start in August, with completion in time for the 2004 football season.

Mike Padgett writes for The Business Journal in Phoenix.

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