Surprise leaks lead to short-term rehab of a 90 year-old water reservoir

 Crack injection

Crack injection was completed with a hydrophilic and flexible polyurethane resin that is NSF certified and suitable for potable water applications. Typically, over 60 linear metres of cracks were repaired each day, using the condition assessment report as a baseline for crack locations and lengths.

The crack injection procedure began by drilling staggered holes at 150 mm centres on either side of the crack, and at 30 degrees from vertical, until the drill bit passed through the base of the crack. Then, plastic packers were hammered into the holes, followed by flushing debris from the crack with pressurized water at 2000 psi. Finally, polyurethane was injected through the packer until the white liquid became visible. The crack sealed as the polyurethane reacted with water, expanded and hardened.

On average, a crack required 0.5 litres of polyurethane per linear metre to be adequately sealed. If more than 0.5 litres flowed through a packer, then it was likely that a void was present beneath the slab at that location. Over 160 m of floor cracks were repaired in CCT#1 and another 160 m in CW#3. Roughly 40 m of very small and previously unobserved cracks were discovered and sealed during grouting.

Grouting of voids

Grouting the voids underneath the floor slab was completed in the winter months. This necessitated a heated and ventilated on-site batching plant and a water source line. The grouting apparatus was small enough to fit through the hatches in CCT#1 and CW#3. It included a grout return line to prevent freezing. Valves for throttling the flow, a magnetic flow meter and an electronic pressure transducer were key elements to ensure quality control.