Penstock Installation With Expanding Grout
Powell Penstock 4 Repair Project – Located in Powell River, BC – Completed in March 2016
Scope of Project
• Removing and replacing two 50’ segments of pipe from under an existing bridge and log flume
• Installation of approximately 350 internal repair plates
• Chemical removal of 60 cu meters of rock adjacent to penstock and intake structure
• Removal and replacement with site assembled expansion joints at two locations
• Refurbishment of existing surge tower
The repairs to a 14 ft diameter, 1580 ft long steel riveted penstock required rock removal directly beside the pipe which could not be removed with traditional blasting methods or rock breaking machines. Due to the rate of detonation in explosions, blasting results in a high level of fly rock, shock waves, and high over pressure creating an outcome that would have left the penstock damaged. If a rock breaking machine was used to remove the rock, the vibrations in the confined space would have damaged the penstock. Additionally, the location of the penstock was in an unfavorable position where a rock breaking machine would have had difficulties maneuvering in order to efficiently operate.
Which GeoBreak Products Were Recommended
The job specifications required a non-explosive demolition where rock splitting motar was used to remove the rock safely while leaving the penstock undamaged. 110 boxes of rock splitting mortar was used on the 240 cubic meters of rock to fracture and weaken the material for speedy removal.
The expected outcome of using the rock splitting mortar was to fracture the rock, weakening the material and making it easy to excavate with a machine.
140 holes drilled, with no damage to the existing pipe. After the expanding grout was applied the contractor was able to machine excavate the weakened rock, further rock breaking was not required.
Final Thoughts From The Project Contractors
This specific job could not have been completed without rock splitting mortar because of the proximity between the penstock and the rock needing to be removed. The challenge was removing the rock without causing damage to the existing pipe, this could not have been accomplished with traditional blasting methods or rock breaking machines. Overall it was a quick and easy process that did not require blasting mats or additional crew for blasting safety procedures. We found that it reduced clean up and produced a precise fracturing of the rock, which let the contractor quickly excavate the fractured rock debris without damaging the existing piping.