Thermal Integrity Profile Analysis of Drilled Shaft and Options for Remedial Measures due to Questionable Results

The subject shaft was part of a large infrastructure project involving the construction of six new stations, additional tracks to accommodate to increase capacity of ridership (50,000 passenger trips per day increase), and electrifying the trains from the current diesel system. The work extends along the existing tracks for approximately 7 miles (11.26 km) between several communities and ends at a private university. The large diameter drilled shafts [7–8 ft (2.13–2.44 m) in diameter and up to 125 ft (38.1 m) in depth] support a new elevated train viaduct structure. The shafts were installed with slurry methods. The subsequent thermal integrity profile (TIP) test performed after a particular shaft was concreted revealed a potential design concrete cover issue (less than required) at a depth between 60 and 72 ft (18.3 and 21.9 m) from working grade. Several remediation measures were evaluated including jet columns to generate the required cover and replacing the exposed rebar by drilling and grouting replacement bars into the shaft. An engineering analysis was performed to confirm the shaft could perform structurally without any remediation efforts. Finally, corrosion analysis was performed to ensure the durability of the shaft was not compromised during the shaft’s service life.