Borrego Springs Photovoltaic Solar Power Plant
Borrego Springs, California
Scope of Work:
- Geotechnical Evaluation
- Geophysical Subsurface Evaluation
- Laboratory Testing
- Geologic and Engineering Analyses
- Written Report
Ninyo & Moore performed a geotechnical evaluation for the NRG Solar - Photovoltaic Solar Power Plant project, including the construction of photovoltaic solar power plants using solar panels at two adjacent sites. One site includes a 41 megawatt plant situated across 300 acres and the other site will include a 15 megawatt plant situated across 180 acres. The solar panels are supported on pipe piles and concrete cast-in-drilled hole (CIDH) piers. Additional improvements include the installation of underground utility conduits and approximately 1-mile of underground transmission line.
Project Challenge: To support the solar arrays, over 20,000 pipe piles were installed at the site. Due to contractor oversight, a small portion of the pipe piles were installed without the benefit of inspection. Since a few pipe piles were installed without inspection, the project plans called for their removal and reinstallation by encasing in concrete. If this process was implemented, it would have delayed the project as well as required additional construction equipment on site.
Innovative Solution: In lieu of the removal and replacement of pipe piles in a concrete encasement, a non-destructive test (NDT) method was used to evaluate pipe pile embedment. Impact echo testing equipment was used on the in-place piles to evaluate pipe pile embedment. Based on the NDT results, the in-place pipe piles were considered suitable and the project continued without interruption.
Services: Services included review of background information; a subsurface exploration including the sampling and logging of 10 exploratory borings and 40 exploratory test pits; performance of a ReMi survey to evaluate site specific shear wave velocities; performance of field resistivity testing; performance of an EM/MAG survey to locate potential buried debris; geotechnical laboratory testing to evaluate soil strength and index characteristics; geothermal testing of site soils; geologic and engineering analysis including seismicity, settlement potential, excavatibility, foundation design capacities, and soil corrosivity; and preparation of a detailed written report presenting our findings and geotechnical design recommendations.