12.07.2015 Views

Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Chapter 12—Renovation of <strong>Conduits</strong>Figure 175.—This gap shows that the designer did not adequately considerthe potential for thermal expansion/contraction during installation of thisHDPE slipliner. To avoid this problem, the HDPE slipliner should have beendesigned to extend beyond the end of the existing conduit.Grouting.—Careful grouting of the annular space between the existing conduit andthe HDPE slipliner is essential. This can be a complex process, requiring theexperience of a qualified contractor. Full encapsulation for the entire length of theannulus rarely is achievable, and the HDPE slipliner is typically designed towithstand all internal and external loadings independently from exterior conditions.A lightweight, low density grout containing no aggregate will ensure the best result.The following guidance discusses the grout plan, mix design, sequencing, andinjection:• Grout plan.—A grouting plan detailing the contractor’s grout mix equipment,setup, procedures, sequencing, plan for handling waste, method forcommunication, and method for sealing and bulkheading the upstream anddownstream ends should be submitted for review and approval prior toinitiation of grouting operations.• Grout mix.—The grout mix, consisting of water, cement, flyash, and chemicaladmixture must remain fluid and not thicken for at least 2 hours. Prematurethickening of the grout will result in high injection pressures, and inadequatesupport of the HDPE slipliner.Cement meeting ASTM C 150, type II is generally considered acceptable foruse in grout mixes for injection. Other types may be considered based onparticular applications. The chemical admixture used will depend upon the type309

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