The intake water supply tunnel for a hydroelectric station was constructed with shotcrete ground support and a spray-on lining to minimize water loss from a high-pressure section of the tunnel constructed through weak ground conditions.
Routine inspection of the tunnel revealed that the spray-on lining had failed at certain locations, allowing water seepage to escape from the tunnel during power plant operation.
The project owner retained Peter White to develop an appropriate repair methodology and to supervise grouting work by a local contractor.
Following a site visit, Peter provided a suitable drilling pattern to accommodate specific deficiencies observed in the spray-on tunnel lining.
Initial test work was undertaken with candidate injection materials and a two-component urethane elastomer was selected that provided performance characteristics that best suited the site conditions.
Peter worked closely with the contractor’s injection crew to undertake the required chemical grouting work, monitoring injection volumes, grouting pressures and connections with adjacent drill holes and defects in the spray-on lining.