A deep bronze bypass pipe positioned between two adjacent water supply shafts had a defective shut-off valve at a depth of 140 m below surface. The general contractor required the deep bypass pipe to be decommissioned by filling with cement grout that met NSF/ANSI Standard 61 for drinking water system components.
Since the water supply system could only be shut down for brief overnight periods when city water demand was low, diving activities were undertaken using two Atmospheric Diving Suits, with one “suit” working in each of the adjacent shafts in combination with remote submersibles (ROV) that provided lighting and underwater cameras to monitor work activities.
The first step in planning the deep dive grouting operation by our grouting engineer was to choose suitable grouting materials. For this project, Type I/II Portland cement and ground granulated blast furnace slag (GGBFS) were selected, both of which conformed to NSF/ANSI Standard 61. No other additives or admixtures were required for this grout mixture.
The second step was to configure appropriate cement grouting equipment to prepare a consistent high-quality grout mixture, provide for redundancy of critical equipment components and incorporate variable frequency drives to facilitate rapid and controlled adjustment of grout flow rates and grouting pressures.
The third step in planning the deep dive grouting operation was to select an appropriate grouting hose for transfer of mixed grout from the surface grouting plant to the point of injection at a depth of 140 m below surface.
After months of detailed preparations, hundreds of diving hours using the Atmospheric Diving Suits, and several days undertaking mockup trials, the grouting operation supervised by our grouting engineer was successfully completed in less than 3 hours from start to finish. The day following the underwater grouting operation, diving crews recovered grouting manifolds from the shaft bottom that were plugged solid with cured cement grout – a positive indication of the state of the sealed bronze bypass pipe.
“Deep Dive Shaft Grouting” – by Peter White, P.Eng.