Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 12—Renovation of ConduitsThese parameters are further discussed in the following paragraphs. On a case-bycasebasis, the designer may need to consider additional parameters, depending onthe performance criteria and design requirements of the specific application.Seepage paths.—For a discussion of seepage paths, refer to section 12.1.1.Service life.—Research conducted by the Trenchless Technology Center atLouisiana Tech University found that the service design life of CIPP liners generallyexceeds 50 years. The inversion tube processes, in which a resin-impregnated tube iscured in place, may not be suitable for lining bituminous coated CMP conduitsunless they are prelined to prevent contamination of the resin by chemicals presentin the asphalt coating (USACE, 1990, p. 3).Initial inspection of the existing conduit.—For a discussion of the initialinspection of an existing conduit refer to section 12.1.1.Selection of the diameter and thickness.—The selection of the diameter andthickness of the CIPP liner should consider the following factors:• Size and condition of the existing conduit.—The size of the existing conduit will limitthe diameter of the CIPP liner. A determination of the condition of theexisting conduit is required to estimate the contributing support. Aconservative assumption would be that the existing conduit is “fullydeteriorated.” For this assumption, the existing conduit provides nocontributing support, and the CIPP lining needs to carry the external andinternal loads resulting from the embankment dam and hydrostatic waterpressures. A less conservative assumption would be an existing conduit in apartially deteriorated condition. For this condition, the existing conduit isassumed to be able to accommodate all internal and external loads for the lifeof the renovated conduit. If the existing conduit is large enough for man-entry,spot repairs of deteriorated areas may be considered prior to CIPP linerplacement.• Discharge requirements.—Similar discharge requirements are needed for CIPPliners as are used for the design of HDPE slipliners; see section 12.1.1 forfurther details.• Clearance requirements.—Grouting is not normally required, since the CIPP linerfits tightly against the interior surface of the existing conduit. However, thedesigner needs to closely evaluate the applicability of a CIPP liner used forlining of a CMP conduit. The CIPP liner cannot tightly fit within thecorrugations, and the ability to grout this annulus would be difficult.325