Las Vegas, host for the 2003 World of Concrete, is a showcase for concrete construction. Nearly every casino on the strip begins construction with a structural concrete frame and finishes with the installation of decorative concrete hardscapes, lakes constructed with structural concrete bottoms, and exotic features such as artificial concrete mountains, statues, and countless other themed features requiring artistic concrete. Excavation and caisson construction are now in progress for two projects on the strip: Steve Wynn's Le Reve Casino, located on the old Desert Inn site, and a new 42-floor tower for the Mandalay Bay Resort and Casino owned by the Mandalay Corporation.

Todd Nisbet, executive vice president for Wynn Design and Development, says, "The Le Reve Casino is an all-new project covering 55 acres and is projected to take 30 months to complete. It will be the pre-eminent luxury hotel and casino resort in Las Vegas, featuring a 3-acre lake, an 8-story mountain on a structural concrete frame, a 1-million-gallon aquatic theater, and a cast-in-place parking garage." With a 36-foot spacing between columns to accommodate larger guest rooms, it will be a heavy building with thicker-than-usual columns and floor slabs. Nisbet adds that the focus throughout the project will be on cost, constructibility, good use of materials, time management, and high utilization of concrete. Marnell Corrao, Las Vegas, is the general contractor for the low-rise structure and the tower and will perform its own concrete work.

In contrast to Le Reve, at Mandalay Bay, Lee Monford, senior project manager for general contractor Mandalay Development, Las Vegas, notes that for construction of the tower, "Our focus will be fast-track, lightweight construction." Mike Dean, president of M.J. Dean Construction, Las Vegas, the concrete contractor for the project, said that its plan is to place one floor every 4 days. The building is scheduled for completion in November 2003.

Soil conditions and caissons

Lochsa Engineering, Las Vegas, is the structural engineer for both Mandalay Bay and the tower at Le Reve. Jess Haldeman, a partner in the firm, states that bedrock isn't available in the Las Vegas valley at a depth to support buildings, only occasional beds of caliche--a cemented soil very common to the Las Vegas area. Given the weight of the structures, Lochsa decided to use caissons as the primary foundations for both buildings instead of "mat slabs," the traditional foundation method for casinos in the valley. When caissons aren't bearing on bedrock, they depend on "skin friction" between the concrete and the rough edges of the caisson hole to carry the load.

At Mandalay Bay, the owner and the engineer decided to use a standard "Kelly Bar" caisson construction method. Drills for this system have auger lengths of 3 or 4 feet. In the Mandalay tower, caissons will be 4 feet and 6 feet in diameter. To install each caisson, the operator of the rig drills 3 or 4 feet into the ground, pulls the bit up, clears the dirt from the auger, lowers the bit back into the hole, and repeats the procedure until the proper depth is reached--as much as 100 feet for this project. If soft material is encountered, the operator inserts a steel sleeve (casing) to prevent collapse. When the borehole has been drilled to the required tip elevation, a reinforcing steel cage is lowered into the hole, and the hole is filled with 8000-psi concrete. Haldeman states that 120 caissons will be needed to support the structure. Each pile cap will be connected to other pile caps by a 2x2-foot reinforced concrete grade beam. Lochsa approved M.J. Dean's request to incorporate a "rat slab" with the grade beams--needed for the start of construction work.

On the Le Reve project, much heavier than the Mandalay tower, original specifications called for the construction of 100 caissons with an average depth of 100 feet. Sixty of these would be 4 feet in diameter, and 40 of them, 6 feet in diameter. After the completion of the shafts, a 31,000-cubic-yard concrete mat foundation would be cast over the caissons to complete the high-rise foundation. The mat foundation was designed to be 9 feet thick, 90 feet wide, and 900 feet long.

As an alternate to the base bid foundation design, Morris Shea Bridge Co., Birmingham, Ala., a contractor specializing in design-build foundation construction techniques, submitted a value-engineered proposal (at considerable expense to itself). It proposed a system of pile caps and grade beams using "continuous flight auger" (CFA). Its proposal would shorten construction time, eliminate the need for a mat slab, and greatly reduce construction costs for the owner. It was awarded the contract after supplying extensive supplemental geotechnical analysis from Western Technologies, Las Vegas; Professional Services Industries, Denver; and STS Consultants, Chicago. It also funded a full-scale static load-testing program conducted on the jobsite.

According to Richard Shea III, the company's vice president, the CFA piles at the Le Reve project will be 1 meter in diameter with lengths ranging from 35 to 50 feet and allowable working loads up to 1500 tons per pile. The CFA pile system requires the use of special drilling rigs. The operator installs the CFA piles by drilling the bit to the proper depth in a single pass. In a process very similar to extracting a cork from a wine bottle, the auger bit is twisted in and extracted without rotation. Simultaneously, 8000-psi concrete is pumped under pressure through the hollow stem of the auger to fill the hole, which ensures that there will be no collapse of the pile walls. An on-board computer monitors the concrete injection to ensure that the proper amount is delivered into the hole. As one might imagine, special rigs are required for this work. As much as 250,000 foot-pounds of torque and 120 tons of extraction force are used to screw in and withdraw the auger.

For reinforcement, a pre-assembled steel rebar cage is lowered into the pile through the plastic concrete. The cage has special spacer wheels wired to the outside of the frame to ensure proper cover for the reinforcing bars.

"The advantage of CFA pile construction is that more `skin friction' is provided between the concrete and the side of the hole. This is possible because the sidewalls of the borehole are less disturbed because the pile is completed in a single pass. Also, concrete is placed under pressure, providing better contact with the sides of the hole," Shea adds.

For both projects, there are two or three caissons to support each column. Therefore, a reinforced concrete pile cap is cast between the building column and the caissons to equally distribute the load.

Building the structure at Le Reve

As previously mentioned, center-to-center column spacing at Le Reve is 36 feet, resulting in a heavy structure. Ceiling heights for the first four floors (the low-rise portion of the resort) will be 18 to 21 feet. Floors will be 11 to 12 inches thick with 10-inch drop panels at the columns and mild steel reinforcement. The column cross sections in this lower portion will be 42x96 inches.

The tower portion of the project has 50 floors. Although the top floor shown on the plans is the 60th floor, there are no floors starting with the number "4," a number regarded as unlucky by Asian gamblers. The tower floors will be 10 inches thick with post-tensioned reinforcement. When the concrete reaches 75% of its design strength, the post-tensioning reinforcement will be tensioned and the formwork removed. The columns for the tower are also larger than the typical column cross section: 24x36 inches for those on the perimeter and 24x96 inches for interior columns. Each deck placement on the tower floor will be 55,000 square feet, requiring 1 week to complete a forming and placing cycle, according to Travis Cubley, Marnell Corrao's project manager.

Claude Trudeau, vice president of Atlas Construction Supply, San Diego, states that his company is providing specialty forms for this project, including wall and column forms and all suspended slab shoring systems. This includes two complete floor levels of flying forms engineered to accommodate both the tower floors and the high shoring heights of 18 and 21 feet for the low-rise portion of the project. The tower has a gentle curve, so the table decks are trapezoidal in shape to allow for curving edges. And, in an effort to allow quick adjustment of column form dimensions and thereby allow Marnell Corrao to stay on schedule despite frequent column height and dimension changes, Atlas is furnishing pre-assembled column forms in four separate increments.

Building the structure at Mandalay Bay

Each floor in the Mandalay Bay tower is 28,000 square feet. Mild steel reinforcement will be used for the first two floors and post-tensioning reinforcement for all the rest. Dean intends to complete a floor every 4 days on the 43-story structure. Patent Construction Systems, Paramus, N.J., is providing the flying table forms for this project. "In order to eliminate the need for reshoring, the tables are being supported by the columns," states Charlie Strandburg, Patent's director of marketing. "Each column is cast with two circular voids, which extend completely through the column. Jack mounts to support the tables will be attached on either side of the column with bolts passing through the holes. A roller pad located on the top of each jack allows for easy placement of the table forms as they are positioned, rolled out, and removed afterward. Up to eight jacks support each form table."

Each form table is 23 feet wide (the width between columns) and 72 feet long. The table is constructed of two structural steel beams that rest on the jack mounts on either side of the table, connected by steel trusses. Aluminum joists are positioned on top of the steel trusses parallel to the columns, with plywood deck attached to the aluminum joists.

The advantages of using column-mounted form tables, according to Patent's director of engineering, Roger Johnson, are:

* No center supports are needed.

* There is less forming material to erect and move.

* Since reshoring isn't needed, other trades can begin their work on the newly constructed floor more quickly.

Shims can be added to the column jacks if column sizes change, but at Mandalay Bay the center-to-center column spacing is 25 feet everywhere, and the column thickness is 24 inches. Only the height of the columns changes to meet structural requirements. Patent is supplying enough table forms to form two floors at a time.

Concrete

Nevada Ready Mix (NRM) is the concrete supplier for both projects. Mike Sherwood, vice president for sales, says that Le Reve will use over 300,000 cubic yards of concrete to complete the project. Mandalay Bay will use approximately 80,000 cubic yards. To supply concrete for the Le Reve project, NRM moved a batch plant onto the site with a 250-yard-per-hour capacity. Sherwood anticipates that the project will need 500 to 700 cubic yards of concrete each day, 6 days a week for the duration of the construction. "An unusual aspect of the Le Reve caisson work," he states, "is that the CFA piles will use an 8000-psi pea gravel mix."

Concrete strength requirements for both projects will range from 3000 to 8000 psi. Mix requirements above 6000 psi will include fly ash, with ultimate strength requirements to be achieved in 56 days. When asked whether there were any other special requirements for the concrete at either Le Reve or Mandalay Bay, Sherwood responded by saying, "In Las Vegas, the word fast is the unique requirement!"

Construction in Las Vegas

As in other parts of the country, Las Vegas' commercial construction market has been slow. The start of these two major projects may propel several other casino projects now in the planning process to follow.

For more information about forming systems contact

Atlas Construction Supply, 602-256-0600 or circle 1 on the reader service card.

Patent Construction Systems, 900-969-5600 or circle 2 on the reader service card.

PROJECT PARTICIPANTS

Le Reve

Owner: Wynn Resorts Limited, Las Vegas

Architect: Butler-Ashworth Architects, Las Vegas

Structural Engineer: Lochsa Engineering, Las Vegas

Geotechnical Engineer: Western Technologies, Las Vegas

Concrete Testing: Owens Geotechnical, Las Vegas

General Contractor: Marnell Corrao, Las Vegas

Concrete Contractor: Marnell Corrao

Caisson Contractor: Morris Shea Bridge, Birmingham, Ala.

Forming Systems: Atlas Construction Supply, San Diego

Mandalay Bay

Owner: Mandalay Corp., Las Vegas

Architect: Klai Juba Architects, Las Vegas

Structural Engineer: Lochsa Engineering, Las Vegas

Geotechnical Engineer: Western Technologies, Las Vegas

Concrete Testing: DSI Inspections, Las Vegas

General Contractor: Mandalay Development, Las Vegas

Concrete Contractor: M.J. Dean, Las Vegas

Caisson Contractor: Anderson Drilling, Las Vegas

Concrete Pumping Contractor: Thornton Concrete Pumping, Las Vegas

Forming System: Patent Construction Systems, Paramus, N.J.

COPYRIGHT 2003 Hanley-Wood, Inc.
COPYRIGHT 2003 Gale Group