Oversized Hole in a Wet Core-Drilled Pier
You are installing 5/8-inch diameter threaded rods into a new interior pier using a two-part epoxy adhesive. The general contractor core-drilled the holes with a 5/8-inch bit, but the bit wandered; field measurement with a bore gauge shows several holes are 11/16 inch in diameter and roughly 5-1/2 inches deep, against a specified 4-1/2 inch effective embedment. The concrete is 28 days old and appears damp in the lower half of each hole. The engineer's spec sheet lists a maximum hole diameter of 5/8 inch for this rod size and a minimum embedment of 4-1/2 inches, and states the adhesive may be used in damp concrete but not in standing water. The rod manufacturer's published capacity tables assume the specified hole diameter. The foreman wants to fill the oversized holes with extra adhesive and proceed.
1. What should you do about the oversized holes, and why is 'just add more adhesive' not acceptable?
Read the worked answer
Do not proceed with the oversized holes as drilled. Adhesive anchor capacity published by the manufacturer is tied to a specific hole diameter and annular gap; the bond stress model assumes the adhesive annulus is within a tested range. An 11/16-inch hole around a 5/8-inch rod creates a gap larger than the tested configuration, so the published capacities no longer apply and the installation is outside the manufacturer's instructions (and therefore outside the code evaluation report). Extra adhesive does not restore the tested geometry; it changes the failure mode and the load path. Options: re-drill to the correct diameter only if that is possible without enlarging further (usually not, once oversized), relocate the anchors per the engineer, or obtain a written engineering solution (e.g., a different anchor type or a manufacturer's oversized-hole approval) before proceeding. Document the condition and get the engineer's direction in writing.
2. The lower half of each hole is damp. How do you handle the moisture, and what would make the hole unacceptable?
Read the worked answer
The spec allows damp concrete but not standing water, so first remove free water: blow out with oil-free compressed air and, if needed, use a water-displacement method approved by the adhesive manufacturer. Then verify the hole is damp-but-not-wet and follow the manufacturer's damp-hole procedure (some systems require a specific primer or a different mixing/nozzle). Standing water, or a hole that keeps refilling, is a stop condition: adhesive will not bond through a water film, and the installation would be non-compliant. If water cannot be controlled, the engineer must approve an alternate method. Record the moisture condition and the corrective action.
3. What installation steps and records should you complete before the rods are loaded?
Read the worked answer
Sequence: confirm hole diameter and depth with a gauge; clean per manufacturer (mechanical brush of the correct diameter, then blow out, repeated); verify cleanliness visually; inject adhesive from the bottom of the hole to avoid voids; insert the rod with a slow twisting motion to the marked embedment depth; allow full cure per the manufacturer's temperature-adjusted schedule before applying any load or torque. Do not torque until cured. Records: hole locations, diameters, depths, cleaning steps, adhesive batch/lot and expiration, cartridge open time, concrete and ambient temperature, cure start/end, and the engineer's written direction on the oversized holes. Any deviation should be captured on a nonconformance report.