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Tehachapi Renewable Transmission Line – Segment 11

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Project Details

Location: Southern California

Client: Crux Subsurface


The Tehachapi Renewable Transmission Project (TRTP) is divided into segments and designed to add 4500 MW of wind generation to the California Power Grid.  Segment 11 involved replacing 20 miles of 220 kV transmission line with 17 miles of new single-circuit 500 kV transmission line. The segment is located within the Angeles National Forest, requiring additional environmental measures.

QS Scope

Quanta Subsurface was the foundation engineer of record for 38 structures, designing micropile foundations for 21 angled and 17 suspension lattice towers.  The design scope consisted of preparing calculations, methodologies, specifications, and drawings to be used for foundation construction.  3D modeling software was used to analyze foundation behavior, including geo-structural interaction, deflection, and pile stresses for multiple combinations of micropile sizes, foundation reveals, loading demands, and geotechnical conditions.  A modified stub angle-to-concrete cap connection was used in conjunction with analysis of site specific surveyed elevations and ground slope conditions to optimize foundation construction, reduce the potential for unsafe excavation heights, and minimize total concrete and excavation volumes for the project.

Engineering services were provided during construction to confirm that foundations were constructed within the assumed design limits, and to provide analysis and solutions for foundation components constructed out of conformance with specifications.  QS also provided construction observation during micropile drilling and installation.  This work included geologic monitoring during the drilling of the piles, observation of reinforcing steel placement, grout sampling and testing, and observation of load testing activities.  Localized geomorphological and landslide mapping was completed.  Sites were accessed primarily by helicopter.  Final compliance reports for the tower foundations were generated at the conclusion of the load testing at each tower location.


  • Foundation EOR for 38 lattice tower structures
  • Designed micropile foundations and oversaw construction activities
  • All work took place within a National Forest, requiring additional environmental measures
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