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Generating Results: Collaborative Team Keeps Alta Wind Energy Project on Track

On the heels of the landmark 2015 climate accord at which nations around the world committed to reducing greenhouse gas emissions, the U.S. government extended tax credits for wind power development. These events led to an explosion of wind power development.

To the Terracon team, the increased support of wind energy as an alternative and clean power source came as no surprise. Our team had recently been a part of the largest wind farm project in the U.S. (second largest onshore wind energy center in the world), Alta Wind Energy Center, for which Terracon served as the geotechnical engineer of record for the last of the project’s eight phases. Located near the town of Mojave within the Tehachapi Mountains in California, this phase included the installation of 60, 3.3 megawatt (MW) wind turbine generators (WTG), a 6-mile transmission line, two large substations, multiple wind measurement towers (MET), buildings, and access roads.

Special Challenges, Specialized Expertise

This project presented various challenges. For example, exploring subsurface conditions for 60 WTGs, half of which had to be placed at the top of a mountain crest. Accessibility was tricky; a few locations were not accessible at all, requiring the team to wait for roads to be built before work could begin.

In order to meet the unique project needs, Terracon brought together a team including five geologists and field engineers to work onsite, two authorized project reviewer (APR) engineers, five project engineers, and five laboratory technicians.

Terracon was able to quickly mobilize multiple drilling rigs, geologists, and engineers from several Terracon offices in order to expedite exploration. The work included 126 borings ranging in depth from 10 to 52 feet and 20 test pits. In addition, geophysical surveys were comprised of Refraction Microtremor (ReMi) and electrical resistivity surveys and in-situ thermal resistivity testing.

To facilitate a quick turnaround for results, testing for soil classification, soil strength, corrosion, and thermal resistivity was performed at three separate offices. Engineering and report preparation included dynamic analysis for foundation stiffness, slope stability evaluation in static and seismic conditions, thermal resistivity evaluation, settlement analysis, deep and shallow foundation recommendations, and unpaved roads recommendations.

Building on Success

Based on the quality of geotechnical work and our strong business relationship with the prime contractor, Terracon was able to help the client with the materials testing. To expedite delivery of this highly time-sensitive project and reduce costs, a mobile laboratory was brought on site. This was especially useful given the fast pace and remote location of the project.

Materials testing was performed by more than 10 field inspectors and technicians, from three Terracon offices. This successful approach was also key during the construction phase. The materials scope of work included inspection and testing of grading operations, deep and mat foundations, concrete and steel reinforcement, bolting, and welding.

Building on our success with the Alta Wind Energy Center project, among others, Terracon continues to expand our expertise in wind energy development. The American Wind Energy Association has recorded an average annual growth of 26 percent over the last 10 years, and with that continued growth, Terracon is ready to assemble the right team for a project at any location.

Fred Buhamdan, P.E., PMP, is the geotechnical department manager in the Orange County office in Calif. He has experience performing geotechnical investigations, engineering design, and project management for various types of projects. Fred's expertise and technical knowledge is focused around power related projects including solar facilities, wind farms, powerplants, transmission lines, and electrical substations. Terracon employees from offices in Orange County and Lodi, Calif., Phoenix, Las Vegas, and Portland contributed to the project described in this article