The largest privately funded construction in the U.S.
The construction is already a small city. Clark County Fire Department will be located onsite, the county has an office for permits and inspections, emergency medical help is available, and there is a ready-mix plant. But with everything under construction at the same time and congestion a major problem, employee parking is offsite and building materials are stored in staging areas on properties near the jobsite. Keeping track of materials and getting them to the site when needed is a large concern. Grantham says that one staging area inventories a large number of structural steel pieces. “We use a bar code system to track each piece so that we will know where they go,” he says.
CityCenter is Perini's first experience with a LEED project so several staff members had to become LEED certified in order to understand the expectations. They had to locate new sources for materials and find out what was used to make them. For instance, Grantham says they had to search out new sources for plywood.
Concrete constructionConcrete is the most used material on the site. Here's how some of the productivity and engineering issues are being handled.
Foundations. In the past, casino foundations consisted of either mat slabs or spread footings. That changed several years ago to include caissons, in part because buildings are taller now. The depth of soil and silt in the Las Vegas valley makes it impossible for caissons to reach bed rock so engineers rely on the “skin friction” between concrete and soil plus attachment to caliche lenses (a local calcium aggregate-based rock) where they occur, to provide additional support. At CityCenter, the foundation system includes 3226 caissons to date, 60 to 100 feet deep and 4 feet in diameter connected in clusters by pile caps and grade beams, supporting mat slabs that the towers are constructed on.
Grantham says that underground congestion has been a major issue involving caissons, underground tunnels, electrical lines, and utilities. In addition, there are sewer lines running through the construction area serving Bellagio.
Forming systems. The tower floors are all “flat plate” construction to reduce the vertical height needed between floors. Aluma Systems', Concord, Ontario, Canada, column-supported table forms are being used for all of the tower construction. For core wall construction, self-climbing EFCO steel forms, Des Moines, Iowa, are being used. EFCO forms also are being used for shear walls and both cylindrical and rectangular columns. The Veer Tower poses special forming challenges due to the tilt of the towers and Doka USA, Little Ferry, N.J., is supplying the forming system for both horizontal and vertical work. The Mandarin Oriental Tower walls and special areas is using Peri Formwork Systems, Elkridge, Md., and Waco Scaffolding Equipment, Cleveland, forming systems.
Concrete requirements. Rinker Material, Las Vegas, is the ready-mix producer for the job and has a batch plant located onsite that provides most of the concrete needs for the project. They supply the rest of it from other locations in the area. More than 60 mixes were developed, with all but a couple of them including some portland cement replacement with fly ash to meet the requirements of 5000, 6000, and 7500 psi compressive strength decks, and 7000, 8000, and 10,000 psi compressive strengths for vertical applications, all depending on location.
Slumps can be as high as 9 inches with the inclusion of superplasticizers for placements with congested reinforcing steel. There is controversy in the concrete industry about where concrete samples should be taken for testing: at the ready-mix truck or at the point of placement. On this project, Perini requires them to be taken at the point of placement to ensure specified performance.
In addition, some architectural concrete is being placed at the Veer tower, requiring special care with regard to forming and placement. Closer to the grand opening, there will be significant amounts of decorative concrete.
Perini is using both crane buckets and concrete pumps with deck-mounted placing booms to place concrete at the towers. Both are in use for the Pelli Tower floors, which are long and narrow. Workers place concrete in the center deck areas with a placing boom and at the ends by crane bucket. For low-rise construction, truck-mounted boom pumps also are used.
