Justice On The Trinity River

McCarthy Building Companies, Inc. broke ground on the new $61.7-million Dallas County Detention Center South Tower this past spring. Upon completion in fall 2008, this 335,000-square-foot, four-story dormitory-style detention center addition will serve as a replacement for two older facilities that must be retired to make way for the Woodall Rogers Freeway expansion and Margaret Hunt Hill Gateway Bridge designed by Santiago Calatrava.

Massive Substructure

The building itself will stand at only 88 feet, yet the piers are almost twice as deep as the building is tall. The building will use about 50,000 cubic yards of concrete, and about 25,000 of those cubic yards are in the 285 piers, according to Val Eldridge, project manager for McCarthy Building.

Because the original Lew Sterrett Justice Center, to which the new construction adjoins, actually sits atop the Trinity River levee just west of downtown Dallas, the piers must be bored down through sand, gravel and loose soil, through the fractured shale layer, and into hard shale.

"The piers are 160 feet deep, and they have to be cased down to 110 feet, the depth at which we encountered fractured shale," explained Eldridge. "Shutte Drilling, who McCarthy subcontracted to drill the piers, had to bore through the fractured shale to penetrate the hard shale. The water table was encountered at about 40 feet."

"It was definitely up there as one of the hardest projects we have worked on because of the soil conditions and depth issues," said Shutte's Matthew Stevenson. "When we have caving soils like this we have to case the piers and these were exceptionally deep. We had to bring a couple of rented service machines into this very tight work area to be able to pick up the 90-foot-long, 60-inch-diameter casing."

It was a slow process according to Stevenson, due to the area perhaps having been a landfill many years ago. "We had to core through concrete and other material, and brought up steel railroad sections and other debris."

"The reason that the piers used so much concrete was because of the voids, or caverns, that could be as large as a room," according to Eldridge. "As Shutte drilled, pockets of sand, gravel and loose soil associated with a river bottom would cave in on the auger." Because the piers are not cased until the auger reaches the fractured shale, the concrete escapes into the caverns as it is pumped in, creating a very deformed substructure.

Terramodel

To lay out the piers, McCarthy utilized Trimble Terramodel, a powerful software package for the surveyor, civil engineer or contractor who requires a CAD and design package with integrated support for raw survey data. With the integrated 3D Visualizer, an engineer or contractor can view their project as an interactive 3-D model.

"The Terramodel helped us tie the new structure into the existing jail structure," explained McCarthy engineer Alfonso Sanchez. "With the Terramodel you are using real time coordinates, not a drafting program, so a foot is a foot, which makes things a lot easier. Since we were able to import the architect's drawings to the computer, it eliminated mistakes and made the survey process go much faster."

"We set the instrument on an established point on the job site," said Eldridge. "From there, we could turn radiuses, pinpoint every pier and every corner. It's come a long way from the old days of surveying."

Tight Site Complexity

The facility will be constructed according to regulations set forth by the Texas Commission on Jail Standards, and will include special materials and security features such as heavy-duty electronic doors that can be remotely secured. Complex tunnels will facilitate transport of prisoners from the sally port, or receiving area, to the secure facility via elevators.

Other challenges include building an underground elevator and a single-level parking garage which will provide additional parking for up to 27 law enforcement vehicles. An unexpected challenge arose when the crew encountered a phone duct bank during the garage excavation.

"We had to relocate the conduits," Eldridge explained. "The phone company pulled the lines, terminated and hooked up the new lines."

"The new four-story, South Tower will connect to the existing Lew Sterrett West Tower," explained McCarthy Project Director James Leppo.

A portion of the new building is key-shaped and is designed to fit into and completely fill an open area 35 feet wide and 44 feet long between existing buildings. After completion of the new building, doors on each level will be cut between the new and existing building.

"Our focus throughout this project will be to minimize disruption to the existing facility during the construction," Leppo concluded.