The Sunrise Powerlink included construction of a new 117-mile high-voltage transmission line in Southern California. Challenges associated with shallow bedrock, mountainous rugged terrain, and environmental regulations all contributed to the decision to use micropiles at 235 of the 438 lattice tower locations.
QS was responsible for micropile and steel pile cap design, as well as overall engineering management for foundation work. Micropile design was based on limited geotechnical data and diverse alignment geology, ranging from stiff clays and medium dense sands to granitic bedrock. The structures were grouped into seven load families, and GROUP software was used to design a matrix of foundation solutions based on the range of geotechnical units expected to be encountered. Ultimate Tests were completed to develop average ultimate grout-to-ground bond stresses in distinct geologic units, which were incorporated into foundation matrixes. This allowed the construction team to optimize pile quantity, cased section length, and bond zone length at each site.
Innovation & Quality Control
The majority of the micropile foundations used an innovative steel pile cap, which was designed to provide schedule and budget advantages over concrete pile caps. Cap design was closely coordinated with micropile design to meet design limitations and maintain tolerances required for construction. Both steel cap and micropile designs were analyzed using a 3D finite element program to virtually test the concepts prior to final design and review.
QS provided field engineering support and construction monitoring services throughout foundation construction. Engineering geologists were onsite during drilling activities to identify and monitor geologic conditions specific to the foundation design. This approach allowed for an efficient and cost-effective set of tower foundations to be installed.