California Crossing
California Crossing
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California Crossing
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Southern California Edison is transmitting wind power from the Tehachapi Wind Resource Area through the Angeles National Forest to support California's growing population, increased energy demand and rising expectations for renewable power resources.

California’s growing population, increasing energy demand and rising expectations for renewable power resources are the driving forces behind the Tehachapi Renewable Transmission Project (TRTP).

When the project is complete in 2013, it will have the capacity to move 4,500 megawatts (MW) of wind power from the Tehachapi Wind Resource Area in Kern County to urban Southern California.

State law requires that 20 percent of the power delivered by California’s investor-owned utilities, including Southern California Edison (SCE), come from renewable sources by 2010. Wind power also helps the state meet the requirements of the Global Warming Solutions Act of 2006, which caps the state’s greenhouse gas emissions at 1990 levels by 2020. Wind generation does not emit greenhouse gases.

Challenges

The first segment of the TRTP to be built, a 26.5-mile, 500-kV line from Antelope to Pardee, crosses the Angeles National Forest, a 650,000-acre area with diverse terrain. SCE needed to coordinate closely with the U.S. Forest Service to minimize the impact on the sensitive slopes. The Forest Service issued a special use permit for 344 acres, covering 60 towers over 13.6 miles of 500-kV line construction and 86 towers over 12.8 miles of 66-kV line removal.

“As SCE’s owner’s agent, Burns & McDonnell is helping design and construct through forest, cliffs and rocky terrain, working in remote locations and inaccessible job sites,” says program manager Ken Gerling. “These challenges make safety and construction planning even more critical.”

Burns & McDonnell is providing project oversight for the first three of the 11 segments planned, a total of 82.7 miles of transmission line scheduled for completion in summer 2010. Segments 4 through 11 are in environmental review.

Solutions

Micropile foundations support 56 lattice towers along the route. The narrow-diameter design minimizes land disturbance and enables construction in rugged environments. Commonly used in urban areas, this project is one of the first to apply this foundation system to lattice transmission towers in the U.S.

Micropile foundations were selected for construction in the forest because they minimally disturb the surrounding environment. A micropile foundation ranges from 4 to 12 inches in diameter and 20 to 100 feet in length. It consists of a casing, single reinforcing bar and neat cement grout. For TRTP, diameters of 5.5 and 8.625 inches are being used with depths between 26 to 45 feet. Groups of three to eight micropiles per tower leg are constructed, depending on the tower type and soil condition.

To further reduce the potential for damage to the terrain, vehicle use is replaced by helicopter transport of crews, equipment and materials. That creates challenges in safety as well as project planning. Weather changes could prevent transport, so sites have all necessary provisions for overnight stays, including food, equipment and first aid kits.

“Crews receive survival training to prepare for the threat of sudden weather changes or forest fires in the area,” Gerling says. “We developed custom technology to integrate satellite tracking into our OneTouchPM® program management software.”

Each crew member is outfitted with a satellite transmitter, similar to what hikers use. OneTouchPM® interfaces with Google Earth Enterprise software to enable live tracking of each person’s location. OneTouchPM® also facilitates communication of program status and schedule, and assists in monitoring sensitive biological and cultural resources along the route.

Results

These unconventional design and construction solutions are helping SCE work closely with the U.S. Forest Service to build and upgrade its transmission network throughout Southern California. The Forest Service is recommending micropile foundation systems for upcoming projects. The techniques implemented are better equipping the state to meet growing energy demands and integrate its renewable generation resources.

For more information, contact Ken Gerling, 909-923-4626.

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