Tunnel Water Inflow Recovery
By Grace Kim 0 Comments

Water Inflow Recovery in a Tunnel Construction Project

Case description

An unexpected water inflow of 1500 USGPM interrupted underwater tunnel construction for a hydroelectric expansion project when an open fracture was encountered that flooded the face of the tunnel and suspended further work until this high-volume inflow could be stopped.

The general contractor requested that Peter White come to the project site and provide hands-on direction of tunnel recovery activities.

Solution

Site inspection revealed that the 1500 USGPM water inflow was associated with a single open rock fracture that was connected to an unlimited water supply from an adjacent lake.

The first stage of recovery was to install several grouting pipes into the flowing aperture, following which a site-fabricated, steel water control gate was installed to cover the aperture location. A temporary wooden sluice was installed through the gate structure to divert as much water as possible through the open gate while subsequent preparations were made.

The perimeter of the steel gate structure was then sealed back to the adjacent rock surface using quick-setting hydraulic cement and water-activated chemical grout that enclosed additional large diameter drainage pipes. After the perimeter seal was in place, formwork was constructed and the steel gate structure was enclosed in concrete.

Prior to the start of cement grouting operations, valves attached to the large diameter drainage pipes were closed, the temporary wooden sluice was removed from the gate and the steel gate was closed and secured. After closing the gate, all of the water flow was stopped, so the only remaining requirement was to fill the water-filled fracture behind the gate.

A high density cement grout was prepared using conventional grouting equipment, with 2% calcium chloride accelerator, and pumped through the available grouting pipes. After placing several cubic meters of high density cement grout behind the steel gate, grouting operations were suspended and the cement grout was allowed to cure.

The following day, probe holes were drilled and confirmed that all open fractures had been sealed by the cement grouting operation.

Photo Gallery

Publication Article

“Tunnel Water Inflow Recovery” – by Peter White, P.Eng.

deep dive bypass grouting
By Grace Kim 0 Comments

Deep Dive Shaft Grouting

Case description

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.

Solution

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.

Photo Gallery

Publication Article

“Deep Dive Shaft Grouting” – by Peter White, P.Eng.