ABSTRACT: Newly developed EPRI capacity evaluation processes for upgrading foundations on existing transmission lines are presented in terms of site characterization and subsurface capacity evaluations. The evaluation process is presented as a series of flow charts the result of a state-of-the-practice literature review and consolidation of over 250 publications. A case history is used to illustrate the application.
GENERAL
A recently completed research study for EPRI resulted in the development of evaluation processes to increase the capacity of foundations on existing electric transmission lines. The proposed processes utilize probabilistic strategies to characterize sites, optimize foundations, minimize costs and better define system reliability. An evaluation philosophy consistent with the desired level of system reliability and potential benefits from upgrades is required. Case history examples illustrate application of the recommended processes.
This paper summarizes the portion of research work involving site characterization and foundation evaluation for rock conditions.
New strategies relying on reliability-based methodologies make use of existing data to identify the general locations of the various subsurface materials and to provide a statistical description of their properties (Spry et al. 1988). Boring sites are selected based upon the initial analysis and additional subsurface data obtained to enhance the reliability in estimates of the engineering properties.
This type of analysis is ideal for upgrading of existing transmission line foundations since initial deterministic-derived subsurface data are probably available to provide a preliminary statistical evaluation of the system. Foundation capacity evaluations are performed after combining information from prior investigations with the new geologic reconnaissance and field exploratory studies.