| Repair


fully fill the borehole and ultimately develop at least 325 psi (22.4 bar) of contact pressure to prevent water passage along the joint. Once hydrated, the waterstop cylinders remain


flexible and accommodate joint movements without restricting the joint. No bond is formed between the concrete and the waterstop cylinder, so the cylinders do not undergo a tension-compression cycle as the joint expands and contracts. This alleviates the fatigue experienced by other waterstop technologies that are subjected to cyclic tension and compression forces when bonded across the joint.


Drilled waterstops project The John Day Lock & Dam is a straight-axis concrete


gravity dam with a powerhouse consisting of 20 monoliths. Commissioned in 1971, the original waterstops had failed and leakage was entering the powerhouse galleries and operating floors along the monolith joints. Excessive flows from joint drains and through the exposed face of the joint was causing water to pool on the floors in critical areas that caused safety and maintenance issues. A pilot project to repair three leaking joints using the CYLutions system was performed two years prior as a precursor to this project. The effectiveness of the repair on the original three locations resulted in this project to repair the remaining joints along the powerhouse monoliths.


Scope of work


At each of 18 leaking monolith joints, a remedial waterstop was to be installed to mitigate the leakage into the powerhouse. A 152mm diameter borehole was drilled vertically along each joint from the top deck to a depth of 1.52m into the foundation. The average borehole depth was 53.9m. Each hole was inspected for voids or honeycombing in the concrete sidewalls of the borehole that could create a potential leakage path around the new seal. Where significant defects were identified, localized repairs were made by placing a neat-cement grout via the tremie method and then re-drilled after cure to reestablish the receptor hole. After a final video inspection, the CYLutions remedial


waterstop cylinders were installed in a column within the borehole up to 1m from the intake deck. A mechanical packer was placed on top of the cylinder stack to resist uplift of the cylinders as they expand in the presence of water.


In the weeks following installation, the leakage at


all joint locations was eliminated. Dye testing that was originally scoped to determine the source of leakage persisting after installation of the waterstops was cancelled, as no visible leakage remained at the joint face or from the joint drainage system at any of the 18 joints.


Looking forward An opportunity exists during the design and


construction phases of dams to reduce future risks and maintenance costs for the facility. Acknowledging that traditional cast-in-place waterstops will degrade due to joint movements and often prematurely fail as a result of construction deficiencies, a vertical small-diameter receptor hole (100mm – 150mm) should be formed along the joint to accommodate future installation of a remedial waterstop, such as CYLutions. This approach will reduce the cost of maintaining the joint in the future, eliminating the need to drill a precisely aligned vertical borehole after leakage develops. Joint leakage doesn’t have to be a persistent nuisance – there is an effective long-term solution to restore the joint waterstop. The CYLutions waterstop system is suited for use worldwide in both new and existing structures, has been installed in more than 100 locations throughout North America, and has supplied remedial waterstops to projects in Scandinavia, Europe and Africa.


Above: Receptor hole aligned on monolith joint


Below: Verifying depth of CYLutions waterstop during installation


Bottom left: Monolith joint prior to CYLutions installation


Bottom right: Monolith joint six weeks after CYLutions installation


www.waterpowermagazine.com | August 2024 | 35


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