Congested Power Plant Site Forces a Hunt for Space
Turning an unused pipe chase into an access tunnel for crews so they can walk safely under a busy street from the parking lot to the site epitomizes the type of workarounds that have kept the 70%-complete 500-MW replacement of the 460-MW Unit 3 Scattergood Generating Station on track. In addition, space was at a premium at the congested 41-acre site in Playa Del Rey. That set off a hunt for ways to fit in all the components of the $950-million job.
"Our most precious commodity on this project is every square foot of space," says Mike Rinehart, general superintendent for Kiewit Corp., the powerplant's engineer-procure-construct (EPC) contractor. "And one of the biggest challenges was getting everything to fit."
There were other site challenges. "The massive sloped hillside that compromised the site prior to project execution required Kiewit to design and build massive retaining walls while excavating and filling areas of the site to yield flat land," says Andrew Gardner, Kiewit's engineering project sponsor. "From an engineering perspective, this posed an incredible challenge due to the geotechnical conditions of the site, the highly active seismic zone as well as the facility's 'importance factor.'"
The project, begun two years ago, will replace Scattergood's 1970s-era Unit 3 power generator with a highly efficient combined-cycle natural-gas-and-steam turbine and two simple-cycle turbines. The equipment is supplied by General Electric under a $260-million contract.
Together, the new turbines will join the plant's existing two units to generate up to 830 MW of electrical power for the owner, the Los Angeles Dept. of Water and Power (LADWP). The turbines have fast start and ramp-up capabilities for short-term increases in electrical demand and for more flexible integration of renewable energy.
LADWP says the new turbines will be 33% more fuel efficient than the existing Unit 3. The project will also replace Unit 3's ocean cooling system with an air-cooled condenser for the combined-cycle unit and an air-cooled heat exchanger for the simple-cycle units.
Mobilizing the Troops
Before Kiewit crews—working under a $441-million contract—could begin erecting equipment and enclosures to house project components, the project leaders had to find lay-down space on a congested site while keeping the essential plant operating to provide power to the Los Angeles area.
To solve the riddle of getting up to 700 workers from the parking lot to the site, Kiewit turned to a 100-ft-long underground chase for oil pipes and other utilities that was used when the plant, which then burned oil, opened in the late 1950s. Kiewit discovered the 10-ft-dia concrete tunnel on powerplant drawings. Crews soon removed leftover piping and converted the chase into a pedestrian walkway for crews to go under Grand Avenue, which cuts across the Scattergood facility.
Because of a scarcity of space, Kiewit designed, installed and commissioned a temporary wastewater system in an unused corner of the facility that would not be disturbed by new construction, allowing LADWP's old wastewater system to be demolished.
This made room for the powerplant and the new wastewater facility that could handle both the existing powerplant and the new one under construction while not interrupting plant operations.
Next came utility work and site preparation. Many uninterruptible services required relocation to different elevations, coordinates or other areas on the site to allow for the site improvements.
"This is my third powerplant, and as far as shifting and putting in utilities, none of them compare to this one," says Tony Chan, LADWP's project site manager. "It's amazing how Kiewit was able to get in between existing utilities and find ways to install all the new utilities."
This included relocating 10,200 linear ft of utilities and installing 63,000 linear ft of underground pipe; 424,420 linear ft of below-grade conduit; 42,580 linear ft of above-grade pipe; 41,190 linear ft of above-grade conduit; 1.65-million linear ft of cable; 12,285 linear ft of cable trays; and 2,500 pipe supports.
"Some of the most challenging relocations included an aging firewater loop passing throughout the site, active aqueous ammonia lines, a high-pressure steam supply to the adjacent wastewater treatment plant and a digester gas supply line from the same neighboring facility," says Matthew Thomas, Kiewit engineering project manager.
All of these systems required intense coordination, careful integration into the final design model and "flawless execution" so they wouldn't need to be moved again, he adds.
Once the amount of space needed for the new powerplant was set, the team determined the locations and sizes of 11 retaining walls, totaling just under 33,000 sq ft. To make room for the walls, designers strategically relocated existing utilities so that they would only have to be moved once.
Selecting the final routing or location for these reroutes was critically important to ensure they didn't inhibit construction activities later in the project nor occupy precious space for remaining elements that had yet to be designed.
Often, the individual problem became a "chicken or egg" conundrum because the ideal location to move a utility required the walls to be in place, says Kiewit's Rinehart. "However, you have to move the utility before the walls could be built," he says.
The walls, some more than 70 ft in height, were designed and built around the existing facility's operational utilities, such as underground gas, high pressure steam, cooling water, condensate, ammonia and firewater lines and underground 230-kV cables.
To build these walls without risking interference with the utilities, Kiewit built a variety of wall systems, such as standard tie-back walls, cantilevered systems and a special dead-man anchor system wall that supports the primary artery of the existing utilities as well as the new facility's utilities, says Rinehart.
It took about eight months to prepare the site before the new power equipment could be trucked in from an offsite holding area in Long Beach.
The design located the combined-cycle turbine and its associated boiler unit just a few feet from a 50-yr-old, three-story-deep basement with retaining walls that were part of the existing Unit 1 and Unit 2 powerplants. The surrounding earth needed to be able to support a 400-ton crane to lift the equipment, which weighed up to 250 tons—or a total load of 500 tons.
To prevent any side loading to the existing units, "we put in a giant concrete block right next to them," says Chan. The block, nicknamed "Sluggo" by the crew, is 38 ft long by 40 ft wide by 25 ft deep and contains 1,400 cu yd of concrete.
The team had examined other options to stabilize the area, such as augered piles or precast concrete piles. Those solutions would have been adequate for the stationary loads of the final design but would not have stood up to the dynamic loads that would be applied to the soil during construction of the boilers, Rinehart says. Sluggo was "maybe not the most elegant solution," but it worked well to transmit the loads, he adds.
With the site prepped, Kiewit began bringing in the turbines, boiler modules and other heavy power equipment for the combined-cycle and the simple-cycle units. Crews used as many as five crawler cranes and a dozen hydraulic cranes to position the units.
"We've had more crane reconfigurations on this job than any other that I've been on," says Rinehart.
On a typical project, they may only have one or two reconfigurations, he adds. But because of the busy site and the size and weight of the equipment, the cranes' angles and placement had to keep changing.
Chan says it took about three months of night deliveries, special road closures and oversize trailers to bring in all the equipment from Long Beach.
Crews are also constructing 63 different structures, including the 31,200-sq-ft, 15-cell, air-cooled condenser structure and a 14,000 sq-ft, four-story control room with parking, a battery room and offices. To save space, the control room, designed by Ware Malcomb and constructed into a hillside by subcontractor Caliente Construction, does double-duty as a retaining wall. The team also built five permanent roads around the site, totaling about one mile.
The project is on schedule for the units to begin operating in December. By then, crews will have excavated 114,800 cu yd of earth and placed 25,700 cu yd of concrete, 800 tons of structural steel and 1,400 tons of rebar.
LADWP says that over the next five to 15 years, it will replace more than 70% of existing power generation with major investments to modernize its infrastructure, meet renewable energy and energy-efficiency goals and eliminate the use of coal power.
