Seepage Management Control for a Dam Rehabilitation Project Using Deep Cut-off Wall Construction and Jet Grouting

Morrison Dam is located on the East Poplar River approximately 12 km southeast of Coronach, Saskatchewan and less than 4 km north of the US-Montana border. The dam has experienced significant seepage throughout its history resulting in deterioration of the concrete spillway. SaskPower is undertaking a two phase rehabilitation program. Phase 1, completed in 2014, consisted of
constructing a soil-cement-bentonite (SCB) and jet grout cut-off wall through the core of the dam and underlying foundation. Phase 2 is being carried out in 2015-2016 and consists of demolition and replacement of portions of the spillway structure, and improvements to the underdrainage and seepage collection system. The SCB cut-off wall was constructed from the dam crest, through the dam core to the underlying bedrock on either side of the existing spillway structure. The SCB wall was designed to produce a low permeability cut-off barrier intercepting two pervious foundation layers (upper sand and lower gravel layers) separated by a clay zone, extending into relatively impermeable mudstone bedrock. Jet grout columns were constructed from the underside of the spillway slab to bedrock and intercepting the SCB cut-off wall, to provide a continuous cut-off wall underlying the service spillway. This paper provides a case history for the cut-off wall construction. Ongoing groundwater monitoring results have shown a reduction in groundwater levels following the construction of the cut-off wall.

Richardson, M, T. Murray, A. George. 2015. “Seepage Management Control for a Dam Rehabilitation Project Using Deep Cut-off Wall Construction and Jet Grouting”, in CDA 2015 Annual Conference, October 5 – 8, 2015, Mississauga, ON, Canada.

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