Case Study: Large Diameter Helical Pile Foundation for High Voltage Transmission Towers in Soft Glacial Deposits-Paper

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The case study describes helical pile foundations for transmission towers on PSE&G’s Northeast Grid Reliability Project near Newark, New Jersey. The sites presented challenging conditions: wetlands and restricted access, high groundwater, organic deposits, and deep, normally consolidated glacial lake clays and silts. Foundations also had to accommodate flood-level pile projections and a tight construction schedule around planned power outages.<br /><br />The piles were 12.75-inch-diameter steel pipes with 36- or 40-inch helices, installed to lengths of 60 or 90 feet. Seven static compression and tension tests were performed. Testing at different intervals after installation—up to 49 days—helped assess soil setup and establish torque-to-capacity factors for production quality control. Early tests showed capacities below initial predictions, prompting additional testing and design adjustments. A mechanical splice was also introduced to reduce installation time; inspections after testing found no adverse effects.<br /><br />The testing supported long-term torque factors of 3.0 for tension and 3.5 for compression. Although some structures required additional piles, the results helped optimize designs and limit redesign. Helical piles proved more cost-effective and required less length than alternatives for comparable allowable axial capacity. In total, 448 piles—34,320 linear feet—were installed in about three months. The mechanical connections and rapid installation enabled the project to meet its critical schedule.

Keywords

helical pile foundations

transmission towers

PSE&G

Newark New Jersey

wetlands

high groundwater

static load testing

torque-to-capacity factors

mechanical splice

cost-effective installation