Technical Manual: Conduits through Embankment Dams (FEMA 484)

Appendix B—Case HistoriesFigure B-9.—When the “hugger band” at the most downstream conduitjoint was removed, the o-ring gasket was found to have been displaced. Inaddition, debris from the pool was found under the band, indicating thatwater may have flowed unrestricted along the outside of the conduit fromthe pool and into the joint.that confirmed that the conduit was placed in a trench with nearly vertical sides,making it difficult to obtain good compaction of the fill soils under and along theCMP and around the antiseep collars.In addition, it was determined that the antiseep collars were installed in locationssubstantially downstream of the designed location. Seepage along the sides of theCMP and under the “haunches” and the resulting loss of backfill soils caused theCMP and joints to deform. Figure B-11 shows the result of seepage along the sidesof the CMP causing loss of soil support, leading to conduit and joint deformation.Lessons learnedA private engineer designed the embankment dam to control stormwater runoffassociated with enlargement of a local shopping mall. The original design engineerwas not onsite during construction, and the contractor was to provide constructionsupervision.The contractor constructed the embankment dam for a local government highwayagency, who also planned to use the pond for stormwater management for a nearbyroad improvement project. The contractor specialized in utility construction, notembankment dam construction. The inspection firm had no control over theB-9