Simplified Reliability-Based Geotechnical Investigation and Design of Transmission Lines

By virtue of their intended purpose, electrical transmission projects traverse large distances across widely varying geologic and geotechnical settings. Thus, the methods by which the geotechnical investigation and design of such projects should be conducted have been a long-standing question by practitioners. Transmission foundation engineers tasked with the investigation and design of projects measured in miles must balance cost effective field investigation with the production of sufficient data for foundation designs that are economical and reliable. A study of the Browning-Pinal Central (BPC) 500/230kV transmission line near Phoenix, AZ, provides insight into a practical approach toward the geotechnical investigation and design of large transmission projects. Paramount to the successful geotechnical investigation of BPC was the careful selection of field investigation locations for soil sampling and in-situ testing based primarily on geologic strata categorization. The subsequent data recovered was used to develop design soil parameters based on simplified reliability concepts. Investigation and statistically based parameter selection concepts utilized on the BPC resulted in a significant foundation cost savings over traditional design practice.