Substation Foundation Types

1. Drilled Shafts

2. Pad Foundation

3. Spread Footing

4. Driven Piles

5. Auger Cast Piles

6. Helical Piles

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Designing strong, safe substations starts long before the construction crew walks on site. And it begins below the surface.

Whether you’re a utility who regularly builds substations or a data center or renewable developer figuring out where to start, this guide is for you. Below, learn what to look for (soil types and subsurface conditions) and how to prioritize needs (budget and schedule) to ensure your project’s success.

Drilled Shafts

Drilled shafts (also known as drilled piers) are often a popular foundation choice because they can be installed quickly. Construction crews drill a circular hole, place a rebar cage inside, fill the hole with concrete, install anchor bolts in the top, and use these to attach the structure to the foundation.

This type of foundation is typically used for tall structures within the substation yard, such as single- or multi-leg structures and transmission line termination structures—offering deep anchoring support with a small surface area.

• Pros: Quick and simple installation; low cost

• Cons: Don’t work well in collapsible or sandy soil, which may cave in before you can pour the concrete

• Use Case: Transmission structures and substation structures

‍Pad Foundations

Pad foundations, or slab on grade foundations, are the shallowest substation foundation option (usually only extending 0.5 to 2.0 feet below grade). They are often used for transformers and other equipment within the substation yard that require a large surface area for support.

• Pros: Quick and simple installation; low cost

• Cons: Shallow and large surface area

• Use Case: Transformers and other equipment

Spread Footing Foundations

Spread footings are deeper than pad foundations, but still a relatively shallow option at about 3 to 4 feet below grade. Crews dig a hole, add rebar, and pour a base (usually square or rectangular). Then, they form a pier on top of the base that extends above grade.

This kind of foundation works well in conditions with a lot of subsurface rock (or the potential for it) below grade. Spread footing foundations reduce the amount of rock removal exposure while offering a strong foundation.

• Pros: Work well in rocky conditions

• Cons: Increased install complexity and cost compared to pad foundations

• Use Case: Transformers and other equipment; rocky subsurface conditions

Driven Piles

Driven pile foundations consist of a cluster of deep piles that are hammered into the ground with a pile driver (usually made of steel, concrete, or wood). Then, a pile cap and pedestal are installed on top of the pile, and equipment is anchored to the pedestals. The piles are usually long pieces of precast concrete, wood, or steel pipe (often 20- to 40-feet long). For deep foundations, one segment is driven into the ground, then the next one is affixed to the top of the previous one, and the process repeats.

Alternatively, you can drive treated timber piles. In this case, you would drill a hole through the top of the wooden pile, insert a piece of rebar in it horizontally, and cast the foundation around that.

• Pros: Foundation stability where soil is loose or area has potential for seismic activity

• Cons: Cost; installation complexity

• Use Case: Transformers and other equipment; loose soil conditions; active seismic regions

Video: 126-foot driven piles for substation project in active seismic zone

Auger Cast Piles

Auger cast pile foundations are installed by drilling an auger into the soil to the designed depth, with concrete or grout pumped through the hollow stem within the auger to fill the cavity created as the auger is removed. A reinforcement rebar cage is placed through the fresh concrete. Then, a pile cap and pedestal are installed on top of the pile, and equipment is anchored to the pedestals.

• Pros: Increased foundation strength compared to pad and spread footing foundations; quietest pile installation

• Cons: More complex and expensive than pad and spread footing foundations

• Use Case: Locations where deep foundations with low-noise and low-vibration factors are required, such as urban areas; quick installation option for sand, gravel, and clay soil conditions

Helical Piles

Helical piles (also known as helical anchors) are essentially large screws that are rotated (screwed) into the ground. Then, a base plate is welded to the top, and the substation equipment is mounted onto the base plate.

• Pros: Fast installation because no cure time is required; strong anchoring capacity due to depth; no excavation needed

• Cons: Can be more expensive than other foundation options; requires specialized installation equipment and expertise; does not work well in rocky or dense soils

• Use Case: Compressed project schedules, where eliminating foundation cure periods saves critical time

As this guide outlines, the driving factors for substation foundations are soil types, subsurface conditions, and balancing design needs with cost and schedule constraints. Using the insights above, you can make more informed decisions and identify the next steps to take as you plan, engineer, and build future substation projects.

Have questions? Reach out to Beta Engineering’s team of EPC experts to ensure your next RFP is set up for success.

About Beta Engineering

Beta Engineering is a substation EPC company headquartered in Pineville, LA, with an office in San Diego. Since 1975, we’ve helped utilities, renewable developers, and other power delivery companies across the U.S. complete high-voltage substation and transmission line projects. Contact our team to tap into 50+ years of problem-solving experience—and a proven commitment to safety.