Abstract:
Muskrat Falls Generating Project is one of the largest hydroelectric projects completed in Canada. Located on the Churchill River in Labrador, Newfoundland, the hydroelectric project consisted of a spillway, three dams and a powerhouse to provide 824 MW of renewable power. A grout curtain was required below the North Dam with installation from inside an existing gallery. The gallery had an opening of 2.5 x 3 m and a total length of 450 meters with access at either end only. Grouting was performed while construction of the Roller Compacted Concrete (RCC) dam continued above. Specialized drilling and grouting equipment had to be employed to allow efficient sequencing of work in a very tight work environment. Challenging rock conditions resulted in further sequencing and logistical challenges as collapsing and hard abrasive rock caused multiple phases of drilling and replacement holes. In addition to the sequencing of work in a safe efficient manner, the management of fluid transport in and out of the gallery had to be carefully planned. High volumes of water were required to be supplied to the drill rig in the gallery to support the water hammer drill method. The resulting waste water and drill cuttings then had to be moved back out of the gallery to maintain a clean and safe work environment All grout batching was performed outside the gallery in a central winterized laydown area and transferred to the grout headers in the gallery. Some significant lessons learned will be discussed with respect to drilling methods, tooling choices, grouting means and methods, grouting in cold weather conditions, quality control and assurance. The focus of this paper is on the challenges and logistics of installing a grout curtain in rock using the GIN Grouting principle from within a precast concrete drainage gallery. Keywords: Gallery grouting, grout curtain, rock grouting