Preplanning, teamwork and communication enable NV Energy to successfully bury six T&D lines for a customer-driven project.
In the 1950s, Las Vegas Boulevard was a two-lane road with a handful of new hotel casinos. Years later, this glittering neon-lined 4.1-mile thoroughfare is alive with visitors and residents 24 hours a day, 7 days a week, 365 days a year.
Over the years, as the Strip has evolved, so have the energy needs and expansion opportunities of local businesses. For example, Harrah's Entertainment, the world's largest provider of branded casino entertainment, owns hotel casinos on three of the four corners of the intersection of Flamingo Road and Las Vegas Boulevard. Repeatedly, Harrah's considered how to expand its guest offerings by further developing this coveted corner of the Strip, but it was confronted with the same barrier time and time again: overhead transmission and distribution lines dissected its properties.
Harrah's turned to NV Energy to bury the power lines. The lines carried three 12-kV distribution circuits, one 69-kV and two 138-kV transmission circuits, all critical to maintaining reliable service to businesses in the vicinity. Burying these lines, which stretched nearly 1 mile, and removing 41 structures would be costly and difficult, but Harrah's Entertainment and NV Energy were determined to make it work.
NV Energy faced two main challenges when trying to bury the lines for Harrah's. First of all, the utility had to discover a way to dig up both sides of a major road that services tens of thousands of vehicles each day. Also, it had to find a way to work and manage traffic in one of the most populated intersections in the West.
The task at hand for NV Energy was to relocate existing distribution and transmission lines underground within the same span of Flamingo Road, without causing any significant outages, while minimizing the impact on businesses within the construction corridor. In addition, the utility was tasked with executing a lengthy and complicated construction plan on one of the city's busiest streets and intersections without the benefit of lengthy daytime road closures.
Solid Planning Sets the Stage
In 2006, representatives from Harrah's Entertainment and NV Energy met with Clark County officials to discuss the project requirements. In addition to the technical and engineering aspects, it was important the NV Energy team develop a plan that would expedite the work in a safe and cost-effective manner. Under ideal conditions, the 1-mile section of Flamingo Road would be closed to traffic during construction and work would take place around the clock. However, given the work would take place in the heart of the Las Vegas Strip, road closures were not an option, nor were 24-hour work schedules.
It was clear from initial meetings with the county that a more creative plan had to be developed.
Using a competitive bidding process, NV Energy chose Wilson Construction as the engineer/procure/construct contractor for the project, with Stantec Consulting as the project engineering firm. Wilson had completed similar projects in San Diego, San Francisco and Vancouver, Canada, and had expertise in underground transmission line construction as well as substation and overhead line work.
NV Energy and the Wilson team had to find a way to avoid underground facilities. This was made all the more challenging by the fact that some facilities had been buried 50 years earlier, and as built records were not available. Crews also would need to excavate across Las Vegas Boulevard multiple times, which meant an increased level of coordination. It also meant crews would need to work overnight to minimize the overall traffic impact.
The initial planning and coordination phase of the project took almost as long as the actual construction, but ultimately, it was well worth the time and effort. Initially, the county assumed directional boring was the only logical approach for this type of project because of the heavy flow of traffic. However, the size of staging areas and excavations required for boring beneath Flamingo Road would require extensive road closures. Therefore, the county approved NV Energy's request to employ open trenching. This approach helped reduce the overall impact on traffic, affecting only two of six lanes at any time during the construction process.
The final construction plan consisted of four phases: trenching, cable installation, circuit and pole removal. Trenching was the longest part of the project. Crews had to dig as many as four separate trenches at a minimum depth of 13 ft along Flamingo Road, often changing the alignment and depth to accommodate existing utilities. At the same time, they had to maintain the necessary separation required for heat dissipation of the electric cables. Each trench was designed to accommodate two transmission or distribution circuits. Unfortunately, this approach would require four separate crossings of the Strip, a proposition that had everyone concerned about traffic congestion and the impact on gaming properties.
Wilson began potholing and excavation in February 2009 using one of the largest production track-mounted trenchers available from Tesmec. Wilson cut a 36-inch-wide by 13-ft-minimum-deep trench through caliche, also known as Mother Nature's concrete. This material, which is found in the Las Vegas Valley, is a hardened deposit of calcium carbonate ranging in hardness as much as 10,000 lb/sq inch. By comparison, typical concrete used for sidewalk or road construction varies in hardness between 3000 lb/sq inch to 5000 lb/sq inch.
Wilson also constructed larger excavations measuring 13 ft wide by 27 ft long by 15 ft deep for vaults to accommodate cable splicing.
The installation of 10 transmission vaults was one of the more challenging phases of the project. The six single-circuit vaults measured 9 ft wide by 25 ft long by 9 ft high, while the four double-circuit vaults came in at 11 ft by 25 ft by 9 ft. The heavier vaults weighed about 100,000 lb. Wilson used a 350-ton hydraulic truck crane to lower each vault into an excavation.
The installation of the vaults required road closures on Flamingo Road. In these instances, the communications efforts paid off immediately. While the project significantly impacted traffic, it received few complaints from business owners, and public and private transportation.
Careful coordination was required to ensure safety throughout the project. The nighttime work — from 9 p.m. to 6 a.m. Sunday nights through Friday mornings — combined with the constant heavy flow of traffic provided continuous challenges for crews. Many times, construction crews assisted emergency vehicles traveling through construction zones.
Crews also were mindful of other utilities during trenching. To ensure the safety of the crews and public, NV Energy emphasized the need for constant communication between Wilson Construction; its civil subcontractor, ARB Inc.; Stantec Consulting; Clark County; and a variety of other businesses and properties.
Expecting the Unexpected
Flexibility also played a key role in the contractor's ability to keep the project running on track. Construction team members responded quickly to a variety of differing site conditions. By relocating work crews when unforeseen conditions arose, the team was able to maintain the project schedule.
In addition to the caliche and other underground facilities, crews contended with groundwater as well. Once crews completed their shift, water would pool in the trenches. Crews pumped out excavations at the start of each work night. The team pumped continuously over the weekend in areas where substantial amounts of water were retained.
The team's flexibility was a critical factor when dealing with construction conflicts as well. On occasion, the county would restrict road closures or require modification to traffic control plans to accommodate other utility projects in the vicinity. The team's ability to adapt and keep the channels of communication open to allow for last-minute adjustments was crucial to maintaining the construction schedule.
Cable Pulling and Splicing
Upon completing the trench and vault construction, Wilson started the cable-pulling operation by handling 30 steel reels that were 12 ft tall and 96 inch wide and about 50,000 lb. The reels were loaded on custom-built trailers that were about 2 ft wider than the average traffic lane. Wilson used a modified puller from Hogg & Davis Inc. with a 1.5-inch pull line to pull cable through the conduit. The procedure was monitored using a dynamometer to ensure tensions did not exceed the manufacturer's recommendations.
Overall, Wilson completed 30 transmission cable pulls within two months, 18 of which were made from underground vaults to self-supporting underground/overhead transition structures. With the successful installation of the cable, splicing of the 138-kV cross-linked polyethylene cable followed. Because of the technical nature of high-voltage splicing, this phase of the project required 24-hour lane closures to ensure crews could minimize interruptions during the splicing operations. The traffic controls, especially during the daytime hours, were key to the safety of the crew and area traffic.
NV Energy crews also successfully managed a complex process of maintaining distribution service while converting overhead facilities to underground. This work included dozens of distribution cable pulls (approximately 8 miles), splices and cutovers, as well as the installation of transformers, switches and capacitor banks. This work required considerable cooperation and teamwork between NV Energy and Wilson crews to clear the path for the last phase of the project.
Wilson completed the final major phase of the project, conductor and structure removal, between May 2010 and June 2010. In order to prepare for this highly visible and critical phase, crews had to do the unthinkable in a 24/7 town: de-energize three major transmission lines and several distribution circuits providing service to the Las Vegas Strip.
To prepare for the scheduled outages, crews had multiple meetings with the impacted properties to help their internal teams accommodate guests during this period. For several hotels, outages impacted air conditioning, food and beverage service, entertainment and rooms. Outages were scheduled for times most convenient to the properties, with the NV Energy and Wilson team completing most of the prep work prior to the scheduled outage to minimize the overall downtime. Thanks to this planning and coordination, the outage periods were reduced dramatically — from the initially planned six- to eight-hour window down to a mere three hours or less.
Structure removal also presented several challenges for the team. The transmission poles averaged 100 ft tall, requiring the use of a 350-ton hydraulic crane. This work required additional traffic restrictions at a time of year when visitor numbers start to increase on the Strip.
In addition to the precision work needed to remove the poles in this congested area, the noise levels that accompanied the work caused concern for hotel guests located near the work areas. Crews again met with properties to provide information before the work began, which enabled hotel staff to provide guest accommodations and enhanced customer service as needed.
Celebrating a New View
The ever-changing Las Vegas Strip celebrates out-with-the-old and in-with-the-new developments in grand fashion. No other city can boast of more building implosions and related celebrations. Yet, the successful undergrounding of such highly visible lines and towers happened with little fanfare and quiet competence. Teamwork, outreach communications, flexibility and tenacity helped this uniquely complex project be completed on time and on budget. Most importantly, the Harrah's Entertainment properties on the Las Vegas Strip can evolve with the needs of their guests.
Adelma Thom (firstname.lastname@example.org) has been with NV Energy for 13 years. As a senior project manager since 2007, her duties focus on the infrastructure requirements for the Las Vegas Resort Corridor with an annual project budget of approximately $40 million.
Ashley Carter (email@example.com) leads the underground transmission group out of Wilson Construction Co.'s Rancho Cordova, California, office. With 13 years of experience in the underground utility market with an emphasis in EHV underground transmission, Carter has managed dozens of projects ranging from distribution through 230 kV across the United States.
ARB Inc. www.arbinc.com
Companies mentioned in this article:
Hogg & Davis Inc. www.hoggdavis.com
Stantec Consulting www.stantec.com
Wilson Construction www.wilsonconst.com