Helical Pier Foundation
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Intro
Helical piers are essentially augers stuck into the ground, which serve as a foundation.
Basic Calculations
Take a 3" helical pier that can hold 12,000 lb/sf on rock or 1500 lb/sf on soft clay, with a safety factor of 2 [1].
- 7000 ft lb torque for screwing 8" diameter helix in [2]
- note that if the pier has 2 helices, that doubles the load bearing capacity! You can stack the helices, but need enough space between the helices.
- Helix is .217" pipe, 3" diameter. Steel Weight Calculator sez it's 6.5 lb/ft. Nice! Helix can be 3D printed with WAAM at $1/lb.
- Thus, the piers are quite affordable. The helix and couplers will be the hard part, that's where WAAM comes in.
Cost
- This article says $150-250 per house pile - [3]
- Average cost of a 20' helical pile - - around $700 - [4]
Examples