This report is a best practices guideline for the evaluation and selection of appropriate transmission line foundations with the least environmental impact. The methodology focuses on the review of published case studies supplemented with selected utility and consultant surveys along with the writer’s personal files on transmission line foundations susceptible to various sensitive and difficult environments conditions. Difficult environments can be classified as wetlands/waterways, mountainous/rough terrain, permafrost/frozen ground, woodlands, conservation/wilderness areas, and desert/rangeland. Utilities often use traditional foundations in sensitive conditions, controlling impacts with construction mitigation measures such as improved access or modular matted paths. Environmental impacts can be mitigated by a combination of good planning, design and construction practices (i.e. avoiding sensitive environments, minimizing activity in these conditions, etc.), or using foundation installation practices that limit construction time. Gaining access for geotechnical investigations in these conditions can be costly, but offers great potential to reduce overall foundation construction cost due to reduced uncertainty. This report details the advantages and disadvantages of both traditional foundation systems (driven piles, drilled shafts, direct embedment poles, steel grillages, spread footings and anchored structures) and alternate foundation systems (helical anchors/piles, vibratory caissons, micropiles, rock socketed anchors and auger cast piles). Local practices, economy, available equipment, and site access generally control the selection of foundation alternatives for projects in sensitive environments.
This guideline presents a great deal of information, options, and alternatives that must be assessed to select the optimal foundation alternative in sensitive environments. Organizing this information is critical to performing logical assessments that arrive at the best foundation alternative for a project. A rational step-by-step model is presented where information is organized, and numerical values are assigned to criteria for each foundation option.
Foundations, Transmission, Sensitive, Environment, Design, Mitigation