A Clever Approach
A Clever ApproachAlternate Traffic Route Developed Near Hoover Dam via an Arizona and a Nevada Construction Approach
STURTEVANT, Wisconsin (October 10, 2005) - Busy, busy, busy … that best describes U.S. Highway 93, which crosses over Hoover Dam. The four-lane, blacktop road serves as a major connector between Arizona, Nevada and Utah, and it is also designated as a North American Free Trade Agreement (NAFTA) route between Mexico and Canada.
However, the heavy traffic volumes and sharp curves on U.S. 93, especially near the highly- visited Hoover Dam, have resulted in a growing number of accidents - 500 in total since 1964. It has also contributed to concerns about potential catastrophes that could cause damage to the Dam and its facilities, contamination of the surrounding waters, and interruption of the power and water supply for the Southwest. After 9-11, commercial vehicles were banned from going over the dam and forced to travel via other routes significantly out of the way.
As a result, the Hoover Dam Bypass Project was initiated to provide an alternate crossing of the river near the Dam. The project is a complex endeavor comprising 3.5 miles of roadway (two lanes in each direction), eight bridges, wild-life crossings, a 2,000-foot-long bridge over the Colorado River and various pedestrian and visitor improvements.
Due to the project's magnitude, it is being constructed in four distinct phases: the Arizona Approach, the Nevada Approach, the Colorado River Bridge, and final roadway surfacing.
In the initial phase, the Arizona Approach highway will work toward the east while the Nevada Approach highway will head west. Both will be connected in the middle at the new Colorado River Bridge, which will span the Black Canyon about 1,600 ft. south of the Hoover Dam.
Construction of the $21.5 million Arizona Approach began in early 2003. The contract for construction services was awarded to the joint venture team of R.E. Monks Construction and Vastco Inc. of Fountain Hills, AZ. Their responsibility encompassed 1.8 miles of four-lane roadway, which leads from Arizona U.S. 93 to the new Colorado River Bridge crossing.
Mountains were literally moved to make way for the roadway and bridge; however, the terrain left behind was extremely steep and rocky. Often, a trail built one day for special access was moved the next. Obviously, these were less than ideal conditions for concrete placing equipment to traverse and set up.
However, the concrete boom pumps used on the job never succumbed to the obstinate terrain and were on-site working about four days a week over a 14-month period. All pumps were supplied by Quinn Concrete Pumping of Las Vegas - the exclusive pumping contractor for this phase. Although every boom pump size from 32 to 58 meters from Quinn's fleet was employed, the BSF 52Z-Meter and BSF 58-Meter Putzmeister boom pumps did the lion's share of the work.
Two-thirds of the concrete placing was devoted to the grid structure, which included underground diversion channels for water drainage. However, the more visually apparent concrete work could be seen on the Sugarloaf Mountain Bridge, a 900-foot-bridge spanning a canyon on the east side of Sugarloaf Mountain. The bridge required eight sets of columns, wide at the base and tapered toward the top. They were constructed in a hopscotch manner, as the specialty beveled formwork jumped from one to the next.
Although all concrete pours were important, the final deck pour of the bridge was by far the most critical. To the casual observer, nothing unusual was evident. To experienced construction personnel, great care was taken to ensure the concrete placing equipment did not break through the new bridge situated 140 ft. above ground.
“The concrete on the bridge was fresh,” notes Steve Heimark, Operations Manager at Quinn Concrete Pumping. “Therefore, instead of nosing up to the edge of the last deck pour and using a smaller boom pump to finish the last 60 foot by 100 foot section, we felt we had to take all danger out of the equation.”
Heimark continues, “As a result, we alerted the general contractor's engineers to help calculate the structural integrity of one of the bridge's column. If structurally sound, this would be a safer alternative for positioning concrete placing equipment over the top of it.”
The column was deemed worthy of withstanding the pressure exerted when pumping concrete along with the combined 260,000 lb. weight of two ready mix trucks and a BSF 52Z-Meter boom pump. With the revised setup spot over top the bridge's column, the larger BSF 52Z-Meter was now needed for more reach.
Although the new setup equation meant a larger sized boom pump, two ready mix trucks could now simultaneously discharge into the pump's hopper. This was in contrast to accommodating only one mixer at a time with the original plan.
Being exceptionally conscious about safety, Quinn also positioned five-foot by eight-foot steel trench plates under the boom pump's front outriggers. This added insurance meant spreading the load over a wider area.
Casino Ready Mix trucks supplied the concrete from a special batch plant set up near the job site. Quinn, owner of the pumping company says, “Even the best Vegas mix is the worst mix almost anywhere else in the country, and the mix specs for this project were no exception. A brutal combination of coarse aggregate and coarse sand proved unpumpable for concrete boom pumps originally sent out on the job. However, when our Putzmeister pump with its Big Mouth S-Valve arrived, it gulped the tough mix down without a problem.”
The Nevada Approach project began in October 2003 and is still in progress. This $30.1 million portion of the project involves roadway construction from the Nevada side of U.S. 93 to the new Colorado River Bridge.
In January 2005, the Colorado River Bridge, which is the heart of the Hoover Dam Bypass Project, started and will take three and a half years to complete. The entire Hoover Dam Bypass Project is expected to be complete in June 2008 at a cost of $234 million.
SPECS - ARIZONA APPROACH
General contractor: R.E. Monks Construction and Vastco Inc. - Fountain Hills, AZ
Concrete pumping contractor: Quinn Concrete Pumping - Las Vegas, NV
Ready mix supplier: Casino Ready Mix, Inc. - Las Vegas, NV
Equipment: Putzmeister BSF truck-mounted concrete boom pumps with models ranging from 32 meters to 58 meters