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by Clair D. Urbain Developers are digging deeper and building taller than ever before on Las Vegas Boulevard, changing the face of the Las Vegas Strip. You wouldn’t expect water problems in Las Vegas, which gets on average less than 6" of rain per year. But if you dig more than 16' below the surface, you’ll quickly run into groundwater that, until now, has discouraged casinos and hotel developers from digging deeper on some of the country’s most valuable real estate. But just like the skyline of Vegas, that’s also changing. “Las Vegas is becoming more urban in its construction methods,” reports Steve DeWees, Perini Building Company project executive who is responsible for the $3 billion Cosmopolitan project. Perini Building Company is a wholly owned subsidiary of the 113 year-old Perini Corporation. “The Cosmopolitan is one of the largest contracts that Perini has ever had. Our portion of the project is approximately $1.9 billion.” As the real estate value on the strip climbs and building sites become more scarce, developers are digging deeper and building higher, and the Cosmopolitan is going where no other building in Vegas has gone – five stories below the surface. The Cosmopolitan is rising on the corner of Las Vegas Boulevard and Harmon Avenue. The 8.5-acre site is bordered by the Bellagio to the north, the new City Center project to the south, and is built around the ’70s-era Jockey Club, which sits almost in the middle of the construction site, says DeWees. The facility will be a full-service casino resort in a mixed-use, high-rise development that will feature:
2005 start date “The soil on the site is varied, ranging from caliche to sand to clay and cement-type soils in the first 20', and then varied soil types below that. With this varied soil, we had to make sure it could support the buildings, so we drilled more than 3,000 holes from the Strip level to 150' deep. These holes were 8" to 12" in diameter in which a 6"-diameter pipe and 2" rebar were placed in the hole and filled with non-shrink grout. These micropiles support the mats that will carry the weight of the complex,” he says. “Eighty percent of the micropiles were put in place from the Strip level; the remaining 20 percent were placed once the excavation was complete. An earthen ramp allowed trucks to enter the excavation, and once the soil was removed, we had to place the micropiles in areas where the ramp was located,” he says. Once the micropiles were placed, crews began excavating the site to 65' deep, which required removing more than 900,000 cu. yd. of soil. “There is an underground river that flows through the site, so starting at between 16' and 20' down, we encountered groundwater. As the ‘bathtub’ excavation continued, we built a slurry wall that was first held in place by tiebacks every 10' that go back into the soil 65'. Also, metal decking will tie the slurry wall to the box columns that also support the building. These are placed on 30' centers,” he says. “The slurry wall is the first of its kind in Las Vegas,” says DeWees. “This is the type of construction you’ll see in bigger cities where the space for the building footprint is precious. With the five floors of underground space, the Cosmopolitan will have nearly 40 acres of parking and holding areas.” Soil from the excavation was relocated to a closed aggregate pit, which took an hour for each round trip. However, during the excavation, that site was no longer available, so the new location was a 1.5-hour round trip from the site. The permanent dewatering system is the first of its kind in Las Vegas, where sloped corrugated pipe that’s covered with porous plastic cloth is covered with pea gravel. The corrugated pipe drains the water into sumps where it is pumped into the storm sewer and eventually finds its way back to Lake Mead. “The water is tested to assure it’s not contaminated and the tests show this water is extremely clean,” he says. Once the excavation was complete, box column construction began. “The box columns are between 2"- and 4"-thick steel and are 3' or 4' square or rectangle columns that weigh 2,000 lbs. per lin. ft. It takes 48 hours of continuous welding to join two sections of box columns together. Once they are assembled, they are filled with concrete. We started them first because they are a part of the critical path. Once they are completed, the rest of the towers and buildings will tie into them using conventional steel construction,” DeWees explains.
Jobsite logistics To expedite deliveries, Perini has modified the building process to increase lay-down and delivery areas and carefully stages incoming loads so materials come off trucks on a just-in-time basis so they can be installed practically as they are unloaded. Loads carrying 60 to 80 pieces of steel start arriving at 5 a.m. to get ahead of the heavy traffic on the Strip. “We even bus our employees in from remote lots because there is no parking available here. We also prefab the concrete forms offsite so they can be just put in place when they get here,” DeWees adds. “We had the southeast corner of the parking garage at the Strip level to be over-designed to support the weight of cement and delivery trucks. In the west tower, we are leaving out some of the lower steel structure so we can actually pull into the tower with trucks and move materials up the towers with manlifts. Tower construction is a 24/7 operation and we plan to have them completed in a year,” he says. Of the 44,000 tons of steel on this project, the box column steel comes from Japan and almost all of the other structural steel comes from U.S. sources. It’s first delivered to a 20-acre lay-down area about 20 miles away from the site. It’s loaded onto trucks in the order that it will be needed for construction so it can be delivered to the site, offloaded and installed almost immediately. “We are working on a five-day cycle per floor. We can really pour a floor a week in each of the towers, so the towers will be completed in one year,” he says. “We are prefabbing much of the work in the towers because of lack of space on the site. Mechanicals, fire protection and even the cooling towers are being prefabbed offsite. The exterior window walls are panelized and the layout of the hotel and condos allows all of the pipe and wire to be precut and labeled for installation. All the plumbing trees are prefabbed,” he adds.
Worker challenges “There were big projects announced in Las Vegas at the same time and everyone thought there would be problems getting material and manpower. We talked to the unions and subcontractors, and luckily the labor shortage eased. Plumbers are hard to come by, but we have worked closely with union halls all along the West Coast and they are getting workers here. We are also finding paper hangers in short supply,” observes DeWees. Crews are working six-day weeks and some are on seven-day workweeks. “There is a full-blown day shift and a partial night shift. There is always something going on at the site,” he says. As the lower floors’ structural steel and decks are put in place, the site, which is about 35 percent complete, is already receiving glass walls and decorative Sicilian stone used throughout the towers. The facility will have 2,200 luxury condos starting at $1.6 million and 800 hotel rooms. The condo space can be rolled into the hotel room pool and both will be managed by Hyatt. With a scheduled opening date of January, 2009, DeWees and Perini remain on track. “We’re getting the exterior glass from China, and it comes to us in containers in order ready to install. The stone and glass curtain walls are starting to onsite now. It appears we will remain on schedule,” DeWees concludes. Published in the March/April 2008 issue of Contractor Tools and Supplies magazine. |
Digging
deep on the strip
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