765kV Load Characteristics
765kV UHVAC lattice towers experience uplift forces exceeding 200 tonnes per leg under broken wire conditions. Compression loads during normal operation can reach 150–180 tonnes. These loads demand foundation systems significantly larger than 400kV or 220kV towers.
Foundation Types for UHVAC
Pad & chimney foundations for 765kV typically require chimney sizes of 2.5m × 2.5m or larger with pad dimensions exceeding 8m × 8m. Pile foundations with 4–6 piles per leg at 600mm diameter and 12–18m depth are common in poor soil zones. Rock anchor foundations are used in hilly corridors.
Geotechnical Challenges
765kV corridors often traverse black cotton soil belts in MP and rocky terrain in Rajasthan and Chhattisgarh. Soil investigation must extend to 1.5× pile length minimum. SBC values below 8 T/m² typically trigger pile design. Seasonal moisture variation in expansive soils requires special consideration for uplift resistance.
Design Standards
IS 456, IS 2911 (Part 1/Sec 2), and IS 8009 govern foundation design. PGCIL and CTU specifications add project-specific requirements for concrete grade (M30 minimum), reinforcement (Fe 500D), and testing frequency. Third-party quality audit is mandatory on most 765kV packages.
Execution Best Practices
Sonil Buildcon executes 765kV foundations with dedicated survey teams for stub setting, daily cube testing, photo-documented progress reports, and pre-pour reinforcement inspection. Multi-leg concurrent casting reduces overall schedule by 30–40% versus sequential execution.