Micropile Foundations | Geotechnical Construction
Wood to Steel TL 678 Transmission Line
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Project Description
TL 678 is part of San Diego Gas & Electric's (SDG&E) Wood to Steel Replacement Program. SDG&E plans to replace more than 5,000 wood transmission poles in rural areas throughout San Deigo County over the next two to three years. The purpose of the Wood to Steel Replacement Program is to reduce maintenance expenses, improve fire safety, and reduce damage to SDG&E infrastructure during fire season.
Team Members
San Diego Gas & Electric, Crux Subsurface Inc., DCI Engineering, Fisher & Strickler Rock Engineering
Crux’s Role
The TL 678 portion of the Wood to Steel Replacement Program involved replacing the existing wood poles between the Los Coches Substation in Lakeside, California, and the Alpine Substation in Alpine, California.
Crux provided SDG&E with a design-build alternative, replacing excavated or drilled shafts with steel cap micropile foundations. Following review, SDG&E accepted Crux's design for the construction of 12 steel cap micropile foundations at 11 wooden pole locations. These foundations were typically for dead end or angle structures.
Drill equipment and supplies were transported to each foundation site by flatbed truck and all-terrain forklifts. Platforms, templates, and spin drills were accurately surveyed and positioned. Standard Penetration Test (SPT) sampling was performed during the drilling of the first micropile at each site to determine the required type and depth of micropiles within that foundation. Micropiles were then installed in a radial array based on specific pole loads and subsurface conditions. Each foundation was successfully proof tested prior to the installation of steal caps.
Specific challenges encountered during the project included accurately orienting the foundations, working within six feet of existing in-service wood poles, low overhead clearances due to energized lines, and environmentally sensitive work areas. The use of Crux's design helped to overcome these challenges, allowing for variable subsurface conditions, reduced site excavation, minimized environmental impact, and the ability to work under existing power lines where workspace was restricted.
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To request additional information, please use our Contact Page or call 866-CRUXSUB (866-278-9782).
