How Are Helical Piers Designed, and When Do They Beat Drilled Piers?

The design starts with the required capacity per pier — from the building loads and the pier spacing the framing allows — and works backward through the manufacturer's correlation to a minimum installation torque. I select the helix configuration (typically two or three helices of increasing diameter) to suit the soil profile from the geotechnical report: larger helices in soft soils, smaller in dense soils, with the lead section reaching the bearing stratum the report identifies. The shaft itself gets checked for buckling in soft soils and for combined axial and lateral loading where the pier sees side load. Lateral capacity deserves honest attention. Helical piers are primarily axial elements; their lateral resistance is modest, so where the structure needs real lateral support — retaining conditions, tall unbraced lengths in soft clay, seismic demands — I detail battered piers, grade beams tying pier groups together, or a separate lateral system. Pretending a field of vertical helicals will handle lateral load on its own is a common under-design I see in contractor-proposed layouts. The drawings show the batter angle, the connection to the grade beam, and the torque acceptance value for every pier location.

Underpinning is where helicals earn their reputation. The work happens in small excavated pits at the existing footing, one location at a time, so the building stays occupied and the structure is never left unsupported. The bracket transfers the footing load to the pier, and a hydraulic jack lifts the settled area back toward its original elevation in controlled increments while I monitor for distress in finishes and framing. The lift is locked off, the bracket is bolted, and the pit is backfilled — then the crew moves to the next location. Sequencing is structural, not just logistical. I specify the pier installation order and maximum lift per stage so the building is never asked to span a gap it was not designed for. On masonry or brittle-finish structures I keep lifts small and watch for new cracking, because lifting a settled building re-stresses everything above. Permitting for underpinning usually runs through the local building department as a structural repair, and in historic districts or dense urban jurisdictions the submittal may need shoring plans and monitoring protocols for adjacent structures.

A helical pier design is ready when it clears this checklist. The torque record is the foundation's birth certificate — protect it. • Geotechnical report identifying the bearing stratum, obstructions, groundwater, and corrosion exposure • Helix configuration and shaft size selected for the soil profile and required capacity • Minimum installation torque on the drawings, tied to the manufacturer's published correlation • Lateral load path detailed honestly — battered piers or grade beams where side load exists • Corrosion protection matched to the soil chemistry and the design service life