Flood Prone Foundations – Taking Pile Caps to New Heights-PPT Presentation

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A 161 kV transmission tower near Clinton, Missouri, was damaged by flood debris, leaving it leaning with missing bolts and bent members. Its foundations were submerged, and the line was critical to local reconstruction work. Because a replacement lattice tower would take 22–26 weeks to design and fabricate, the owner chose to stabilize the tower and plan a full replacement.<br /><br />The replacement structure was a 145-foot tubular steel tower. Engineers selected micropiles and steel pile caps instead of conventional drilled piers, citing challenging construction access, potential excavation loss, scour, concrete curing time, and the need to work beneath energized conductors. Nearby geotechnical exploration found stiff clay over alternating sandstone, shale, and limestone.<br /><br />The foundation design accounted for variable ground conditions, corrosion, buoyancy, scour, and flood loads, including hydrodynamic forces and debris impact. It used four battered, cased micropiles at each foundation, designed for multiple combinations of tower loading and flood stages. The pile caps accommodated a 16-foot reveal and enabled the tower structure to be installed soon after foundation work.<br /><br />Fabrication required careful weld inspection, including ultrasonic testing of complete-joint-penetration welds and magnetic-particle testing of fillet welds. After galvanizing, apparent cracks were investigated and ruled out as weld defects.<br /><br />Construction began in January 2022. Drilling and grouting were completed, the piles were proof-tested, and the pile caps were installed by January 24. The site was then handed over to the structure erection crews.

Keywords

transmission tower

micropiles

pile caps

flood damage

clinton missouri

tubular steel tower

foundation design

scour

weld inspection

construction access