The Value of Structure-Specific Borings: Statistical Analysis of Electrical Transmission Line Structure Foundation Costs Based on Structure-Specific Borings versus No Borings or Variable Boring Spacing

Transmission line structure foundations are often designed without soil borings at each structure due to schedule and/or budget constraints. This paper presents a statistical analysis using soil boring data obtained at more than 2,000 structures for a high-voltage transmission line, encountering variable subsurface conditions over its 375-mile length. The analysis compares foundation designs based on structure-specific boring information to theoretical designs resulting from presumptive design parameters or parameters from borings obtained at various intervals. Soil and rock parameters for hundreds of structure locations have been regenerated, applying assumptions to reflect those that would be made if boring data was not available at every structure. The results reveal substantial schedule and cost savings when borings are obtained at each location, due to foundations that would have been over-designed or under-designed with fewer borings. In some cases, foundations could have been designed without accounting for adverse subsurface conditions, such as shallow rock, which would have resulted in construction delays if encountered without structure-specific boring information.