|John Bunje, project manager for Rudolph & Sletten, points out tied-in root that makes the exhibit's shotcreted walls look like an African mesa.|
Tour buses at the San Diego Zoo are making a detour to view rarely seen creatures at the park these days: human construction crews in hard hats operating yellow CAT wheel loaders, Hitachi excavators and a variety of other equipment. The human species looks at home in this habitat as it prepares some 7 acres of a former 50-year-old site that had exhibited giraffes and other hoofed animals and is now being prepared as a habitat for elephants and other animals.
About three of the acres will be the elephant's portion. The rest will become home to pronghorn sheep, tapir, capybara, California condor, turtles, snakes, and more. There will also be a new merchandise area, restaurant, two filtration yards supplying life-support systems to the exhibit pools, as well as new water features.
Shotcrete crews, wheel loader operators and excavators have to be quiet at certain times on this job site. After all, the San Diego Zoo is home to rare and exotic animals that don't like a lot of noise and vibration. And visitors from around the world want to experience a quiet trip to the Zoo.
“That's one of our major challenges,” says John Bunje, project manager for Rudolph and Sletten, Inc., overseeing construction management for the Elephant Odyssey. “We've learned when to sequence moving to different parts of the work site to keep noise to a minimum. We've also had to shut down equipment while a nearby daily animal show is being conducted just on the other side of the south drop-off, at the Hunte Amphitheatre. This happens sometimes two or three times per day.”
But Bunje says his major challenge is the 7-acre site itself. With elevation differences, it's difficult to see the entire operation from a single vantage point.
“With so much construction going on in various places, plus a lot of underground work right now, we're having to coordinate site utility systems while we are preserving (animal) life support systems – irrigation piping, electrical work, structural footings and foundations, and various retaining walls at different elevations.
“Coordinating all of the designers and specialty consultants that a zoo project needs requires more time and attention than with a 'standard' building project. Many of the ideas that go into basic design and construction are not applicable due to designing for keeping exotic animals in the exhibits, not to mention dealing with the strength and size of a 10,000-pound animal. This requires some serious structural work, beyond that of anything I've built in the past.”
Crews of up to 200 workers per day are on site. There is some off-haul of soil to other Zoo locations, and some recycling, including former concrete buildings (approximately 1,000 cubic yards of crushed concrete from the old exhibits), has been used as base on site.
There is a series of 10- to 14-foot wall sections stubbed into footings with a keyway underneath to resist rotational overload, Bunje said – with 4,000 psi cast-in-place shotcrete.
Shotcrete is hosed into place in 4-foot lifts. Once concrete sets (in about a seven-day cure time), natural-looking tree roots are tied-in and a plaster coat is applied that has an earth tone color. While still wet, earth is applied, giving it a natural mud-bank finish.
The shotcrete is a 4,000-psi mixture, compliant with ASTM C-150, the same as other structural concrete. It uses a water-reducing admixture to help it stand up and has a 2-inch slump (versus the standard 4-inch slump for most pumped mixes). The mixture consists of 3/8-inch aggregate, fly ash and sand. It is supplied by Vulcan Materials Company and applied by SJ Rocks.
Shotcrete is applied at approximately 200 psi for the structural concrete, and 60 psi to 100 psi for the topping coat. Rebar sizes vary with wall height, mostly No. 3 and No. 4 bars.
“Trying to build, keeping in mind that animals will be housed on one side of this project and families with small kids will occupy the other side is a challenge,” says Bunje. “You've got to think about what a two-year-old would want to grab onto, climb over, etc. When doing the design review, changes happen constantly as a result.
“But, it's a lot of fun to be a part of, and to construct what people from all over the world will see and experience here at the San Diego Zoo,” he said.
The Elephant Odyssey project began in September 2007, and completion is scheduled for spring 2009.