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Western Dam Engineering <br /> <br /> <br /> <br />21 <br />etc.). Many common mechanical repairs consist of a <br />rubber seal with a stainless steel band that helps to <br />compress the rubber seal against the conduit by <br />expanding the band once in place. It is important that <br />any mechanical repairs implemented within the <br />conduit be tapered at the ends to minimize flow <br />obstruction. Because seepage can sometimes extend <br />away from the conduit, it is important that repairs like <br />these are monitored by regular exterior and interior <br />inspections to ensure no new signs of internal erosion, <br />backwards piping, or seepage into or along the conduit <br />develop. <br /> <br />Photo 7: Link-Pipe Grouting Sleeve after installation <br />over cracked conduit. <br />Metal Conduits <br />The most common metal pipe used today in <br />constructing conduits through embankment dams is <br />steel. Steel pipes are typically used as liners in RCIP <br />conduits. These conduits are typically delivered to the <br />job site with the interior painted from the factory and <br />the exterior bare steel. The pipe is typically set into <br />place and the joints welded together. The factory- <br />applied coating along the interior of the conduit stops <br />about six inches short on either side of the joints (to <br />allow space for welding) and has to be painted in the <br />field after assembly. A reinforced concrete <br />encasement is cast-in-place after the conduit has been <br />water tested and accepted for use. <br />Photo 8: Sandblasted steel surface in preparation for <br />applying new epoxy coating at joints. <br />Corrosion <br />A common maintenance issue for steel liner encased <br />conduits is deterioration of the coating system and <br />corrosion of the conduit. Because the joints are <br />painted in the field, the coating at joint locations often <br />deteriorates faster than other portions of the pipe. <br />For that reason, proper care and quality control is <br />critical during construction. Remediation of the liner <br />coating system typically includes sandblasting the <br />interior of the liner to expose the bare steel and <br />applying two coats of high solids epoxy paint (typically <br />~7 mils per coat). <br />Voided Encasements <br />Another common issue in steel liner encased conduits <br />is voids within the concrete encasement due to poor <br />consolidation of the concrete. This issue is most <br />prevalent in encasements that are constructed <br />monolithically (no horizontal construction joints). In <br />these cases, consolidation beneath the steel liner can <br />be difficult during construction. Voids behind the steel <br />liner are usually detected during a conduit inspection <br />from visual confirmation of seepage at the <br />downstream end of the encasement or the sound of <br />water moving behind the conduit. <br />Sinkholes, depressions, or cavities on the surface of the <br />embankment, along the conduit alignment, can <br />indicate piping and the potential for voids within the <br />encasement. Because of the presence of the welded <br />steel liner, seepage into the conduit is typically not an <br />issue. Repairs to voided encasements are generally <br />made by injecting grout behind the steel liner. <br />Pressure grouting behind the steel liner is done via