Helical Piles: Reinforcement of Broken Foundations After Five Years of Installation-PPT Presentation

PPT Presentation

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The presentation examines repeated failures of helical-pile guy anchors on a 328 km transmission line in Brazil’s Piauí region, where ruptures began about five years after installation. The area has dry, erosion-prone soils of sand, silt, and clay, with occasional heavy rainfall.<br /><br />Field inspections found displaced piles, misaligned tower masts, and stressed insulators that threatened power-line operation. Review of the original design and installation records identified concerns about geotechnical capacity and structural resistance to installation torque. Calculations indicated that the piles’ theoretical capacity was below the required tension loads at several locations. Installation torque requirements could also approach or exceed the shaft’s structural limits. SPT results varied between surveys, while installation records showed torque rising rapidly in some soil layers.<br /><br />Laboratory testing indicated substantial soil-collapse potential when wetted. This suggests that moisture changes, including increased rainfall, may affect anchor performance. The study also noted that collapsible soils in the region were not represented on Brazilian maps.<br /><br />The reinforcement design added two new helical piles connected by a transition beam, without relying on the capacity of the existing pile. Before permanent installation, six sites were tested to assess torque and load capacity. The reinforcement was designed with a safety factor of 1.75, and the beam was checked for structural performance.<br /><br />The authors emphasize the importance of thorough geotechnical investigation, installation verification, and clear understanding of safety and load factors. They also recommend considering soil collapsibility, rainfall-related moisture changes, and minimum pile embedment in the design of foundations in tropical soils.

Keywords

helical-pile guy anchors

transmission line

geotechnical failure

soil collapsibility

installation torque

anchor reinforcement

Piauí Brazil

power line foundations

SPT results

rainfall moisture effects