The project consisted primarily of two new 500 kV transmission lines built within existing corridors – one 111-mile line and one 42-mile line. Crux Subsurface was selected to provide micropile foundation design-build services for 43 lattice towers and 13 permanent helipad structure locations due to challenging subsurface conditions and limited access.
QS was responsible for all aspects of micropile foundation design and field support. Geotechnical design parameters were established for anticipated subsurface conditions, and a decision matrix for foundation installation was developed. Standard penetration tests were performed during installation to confirm subsurface conditions, and combined with the matrix to optimize pile quantity and length at each foundation location
Advanced analysis techniques, including the strut and tie method, were used to design concrete pile caps with less reinforcing than conventional methods. Additional design services included recommendations for an ultimate load testing program, geotechnical design review, and design support during construction. QS also supported the prime contractor in determining slope/excavation stability per Cal/OSHA standards, designing remediation and reinforcement where required.
Geotechnical variability created foundation design challenges. Conditions ranged from loose sand to highly weathered bedrock, with slopes varying from flat to 45 degrees. Using unique methodologies to determine soil resistance at sloped locations, QS was able to optimize tower elevations at micropile foundation sites. This optimization effectively decreased required excavation and concrete volume required for the pile caps, positively contributing toward project cost and schedule.