Micropile Foundations | Geotechnical Construction
Tehachapi Renewable Transmission Project - Segment 1
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Project Description
Southern California Edison’s Tehachapi Renewable Transmission Project (TRTP) consists of upgrading several segments of high-voltage transmission line from 220 kV to 500 kV. TRTP includes several segments and is necessary to integrate new levels of state-mandated wind generation in compliance with California's Renewable Portfolio Standard. Upon completion, the transmission system will be capable of delivering 4,500 megawatts at full capacity, which is enough to provide power to over 3 million homes.
Segment 1 of TRTP entailed rebuilding 26.5 miles of 220 kV lattice tower transmission line between the Antelope Substation in Lancaster, CA and the Vincent Substation in Santa Clarita, CA. Approximately 12 miles of the alignment are located within the Angeles National Forest, where new road construction is not permitted and access by vehicle is limited to existing United States Forest Service (USFS) roads.
Team Members
Southern California Edison, PAR Electrical Contractors Inc., Crux Subsurface Inc.
Crux’s Role
PAR provided construction services for this segment and subcontracted Crux to provide foundation design and construction services on the 12-mile section within USFS land. Crux provided an alternative design option, replacing traditional excavated shaft foundations with micropile foundations at 56 tower locations. Following a design review of these micropile foundations, Southern California Edison accepted Crux's design for construction.
A key component of the design was to provide a foundation system able to accommodate variable subsurface conditions and tower loads without changing materials or equipment. The design was tailored to obtain subsurface characterization during the drilling of the first pile, allowing Crux to quickly adjust the number and depth of piles required for each site.
Due to the lack of road construction, drill equipment was transported to tower sites using medium- and light-lift helicopter support. Platforms were transported to each tower leg location to support the drill template and spin drill. Micropiles were then installed on a radial array based on the specific tower requirements. Concrete caps were used to transfer the load from the stub angle to the micropile, and proof testing of was conducted at each tower site prior to completion.
Utilization of Crux’s micropile foundation design allowed for minimized site excavation, less required concrete, reduced safety concerns associated with hand dug shafts, and a foundation system able to accommodate variable subsurface conditions and tower loads.
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