OasisLMS

Abstract: A new 20-mile, high voltage transmission line was recently designed and constructed by the Salt River Project (SRP) in Central Arizona. Drilled shaft reinforced concrete foundations were used to support the predominantly laterally loaded monopole structures that cross through several geologic regimes. SRP and their geotechnical consultants elected to optimize foundation design by following a rational approach in terms of construction schedule, total installed cost, and reliability. The process involved management of foundation data during both design and construction to minimize schedule and cost risk from unanticipated conditions that were likely to be encountered during foundation construction. This paper details the engineering approach that involved (a) a geological desktop study to select representative locations for subsurface sampling and testing (one boring for every 5 to 6 structures), (b) a statistical approach to estimate characteristic geotechnical design properties along with development of idealized design profiles, and (c) a foundation inspection program that included detailed logs of soil conditions at each structure site. This process allowed for rapid real-time design changes during construction to account for encountered conditions that differed from design assumptions. To facilitate ease of application and use by the utility and their geotechnical consultants, documentation and management of foundation data was performed using spreadsheets in lieu of typical construction management software. The paper also presents a comparative assessment of the optimized program with other approaches used in the industry (testing and sampling of all structure sites to reduce change risk; using low-bound geotechnical design properties to provide more conservative but more costly foundations to reduce construction risk). The optimized program resulted in a less than 5% change in foundation design due to unanticipated construction conditions and was less costly than the other options while providing a high level of knowledge on foundation and subsurface conditions for improved system reliability.

Mr. PETER M. KANDARIS; Mr. JAMES ADAMS

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