|Underwater repair methods…
|Methods for placing concrete underwater and special mix designs allow virtually any type of concrete repair, or even construction, to be undertaken. Defects from minor spalls to extensive structural deterioration can be addressed.
|Underwater leak sealing
|A repair may involve sealing a leak at one point, or an overall surface repair covering many possible leak points. Localised repair of individual cracks can prove costly if the leakage is propagating through an extensive network of cracks.
|Pressure grouting cracks
|Chemical grouting allows extensive crack networks to be treated simultaneously. Chemical grouts are injected as low-viscosity solutions under pressure. They react with water or a catalyst after a predetermined time to form a plug. Water-activated polyurethane grouts expand on contact with water and adhere tightly to the walls of the crack. Flexible hydrophilic foams are regularly used in crack injection. Gels with a shorter reaction time are effective in stopping large-volume water flow.
|Sealing large voids
|Filling large voids usually involves the placement of concrete Concrete can be pumped to the driver continuously, minimising the surface area of the concrete in contact with the water. Divers can even manoeuvre the concrete hose onto areas where access is difficult, such as deep voids on a vertical face. Pumping distances of several thousand metres are possible if hard pipe is used over most of the run.
|There is a point where pressure grouting and concreting become ineffective and costly. An alternative is to install an impervious synthetic membrane across the full upstream dam face. If there is seepage under or around the dam, the barrier should be extended to the approach bottom and abutments.