Drilled Shaft Flexure Reinforcement Repair Case History-PPT Presentation

PPT Presentation

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This case history describes the evaluation and repair of drilled-shaft foundations supporting a 1.1-mile overhead transmission line with 16 structures. Construction deficiencies included inadequate concrete cover, too few cage centralizers, reinforcement-cage racking, and shaft squeezing. The shafts were 6–9 feet in diameter and embedded 20–55 feet.<br /><br />The team reviewed thermal integrity profiling (TIP) data, construction records, photographs, and loading information to identify sections with insufficient flexural reinforcement and compare shaft capacity with moment demand. For Shaft 5, the original flexural capacity was adequate near the top, but capacity at critical sections was only 4,000 kip-feet against demands as high as 13,100 kip-feet. The repair design added five Grade 75 No. 24 reinforcing bars, post-installed to a length of 36 feet, increasing capacity in the deficient sections.<br /><br />Repairs involved protecting anchor bolts and installing formwork, coring and drilling holes, flushing them, then placing grout and wet-setting the reinforcement. Concrete–grout bond testing was also conducted.<br /><br />Four 9-foot-diameter shafts were repaired; analysis found the remaining 12 shafts acceptable. The project concluded that post-installed reinforcement can effectively address flexural deficiencies, while TIP data can provide valuable, relatively low-cost insight into the performance and long-term reliability of critical transmission-line foundations.

Keywords

drilled-shaft foundations

transmission line

thermal integrity profiling

flexural reinforcement

post-installed reinforcement

shaft repair

concrete cover deficiencies

reinforcement cage racking

shaft squeezing

bond testing