Helical Piles: Rupture after five years of installation-Video

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Video Summary

Daniel Reynoso and Howard Perko present a case study of helical-anchor failures on a transmission line in Piauí, Brazil. Five tower structures collapsed after anchors pulled out, and inspections found movement across the line. Investigations showed that the installed anchors had inadequate geotechnical capacity and insufficient installation torque; their shafts also lacked the strength needed to achieve higher safety factors. New soil borings revealed lower SPT blow counts than the original investigation, which may have overestimated soil strength. Laboratory tests further identified serious to very serious soil-collapse potential when wetted, a hazard not shown on regional geological maps. The consultants classified tower criticality and designed a retrofit using two additional anchors and a connecting spreader beam, with repairs starting at the most critical structures. The case highlights the importance of reliable soil testing, appropriate torque-to-capacity ratios, adequate safety factors, and careful consideration of collapsible soils and changing rainfall conditions.

Keywords

helical-anchor failures

transmission line collapse

soil geotechnical capacity

collapsible soils

anchor retrofit design