Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 12Renovation of ConduitsThe selection of the proper method for renovation, replacement, repair, orabandonment of a conduit is very site specific. Many factors go into the selection ofthe method to be used. This chapter will address design and constructionconsiderations for the renovation methods. Chapter 13 discusses replacement ofconduits, and chapter 14 discusses repairs and abandonment of conduits.When evaluating older structures for renovation, the designer should proceed withcaution. Previous designs may have utilized differing criterion or loadings comparedto what is used in modern conduit design. The designer should consider materialsavailable at the time of construction, and changes in material properties, designpractices, and construction methods. For example, reinforcing bars used inreinforced concrete have undergone significant changes in the last 100 years. Yieldstrengths, allowable stresses, bar shapes (e.g., plain round, old-style deformed,twisted square), and splice lengths all have changed, compared to what is used todayfor modern structures. If original design information is not available, the designerwill need to make conservative assumptions. The designer may find it beneficial toconsult references that contain information on old design and construction methods.An example of this type of reference would be the ACI Detailing Manuals (availablesince 1947) (Concrete Reinforcing Steel Institute, 2001, p. 2). The designer couldutilize these manuals to determine typical reinforcement details commonly usedduring the period of design.The understanding of a historical timeline can often assist the designer withidentifying conduits that may remain relatively free of long term deterioration andthose that may require actions for renovation, replacement, or repair. Typically,timelines cannot specifically identify exact dates or structures when changes inmethods or materials may have occurred because most of the available informationis based upon a collective understanding that evolved over a period of time.Available timelines in many cases may be agency specific. An example of a historicaltimeline developed by Reclamation is illustrated in figure 158. This timeline wasdeveloped based on significant events that have occurred in regards to theirexperience with concrete technology. Using a timeline such as this, if the designerknows the approximate date of construction for a particular conduit, a preliminaryassessment of its likely condition can be made.289