Erosion from rising storm water can damage or weaken existing transmission line and substation foundations. In flooded areas, drilled shafts and driven piles need to be inspected to see if there is damage. In the event of flooding, follow this foundation inspection checklist:
Ground water can degrade surrounding soil structure, and therefore reduce drilled shaft capacity. The ratio of minimum rebar spacing to maximum aggregate diameter should remain at no less than three to five, according to the U.S. Federal Highway Administration.
NOTE: The capacity of drilled shafts is developed from a combination of side shear and end bearing. In other words, as the load on the shaft increases, the load taken by the side shear is large, while the load taken by the end bearing is small.
Look for erosion that exposes drilled shaft or driven pile foundations. Exposed shafts can not only result in reduced capacity, but compromised uplift/lateral/bearing integrity.
Inspect the structure for other flooding damage, which is often evident through settlement movement.
Foundation inspection checklist: Next steps
Utility crews can do a few things when repairing structures after a storm. Solutions include:
- Augment the existing foundation using helical piles.
- Build a new foundation using helical piles and steel grillages.
These solutions often require an engineered approach from supply chain professionals, with whom transmission line owners and their consulting firms can match helical pile design to site-specific soil conditions and load requirements.