Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams188review of plans and specifications for the project. In the case of existingconduits, problems resulting from poor detailing should be handled bycorrecting the detailing and not by simply responding to the symptoms.• Poor construction practice.—Not following specified procedures and techniquesmay result in construction errors. While individually these errors may not leaddirectly to failure, when grouped together they could lead to the developmentof defects that could adversely affect a conduit’s integrity. Construction errorscan occur during new construction, renovation, and repairs. In concrete,cracking and spalling can be a symptom of poor construction practice.Common construction errors include:1. Improperly located reinforcement.—Reinforcement that is improperly located oris not adequately secured in the proper location may lead to two generaltypes of problems. First, the reinforcement may not function structurallyas intended, resulting in structural cracking or failure. The second type ofproblem stemming from improperly located or tied reinforcement is oneof durability. This involves reinforcement that is improperly located nearthe surface of the concrete. As the concrete cover over the reinforcementis reduced by wear, it is much easier for corrosion to begin.2. Improper alignment of formwork.—Improper alignment of the formwork leadsto discontinuities on the surface of the concrete. This occurrence iscritical in areas that are subjected to high velocity flow of water, such aswhere cavitation-erosion may be induced.3. Adding water to concrete.—Water is usually added to concrete at the deliverytruck to increase slump and decrease emplacement effort. This practicegenerally leads to concrete with lowered strength and reduced durability.As the water/cement ratio of the concrete increases, the strength anddurability decreases.4. Improper consolidation.—Improper consolidation of concrete may result in avariety of defects, the most common being surface air voids (also knownas bugholes), honeycombing, and cold joints. Surface air voids are formedwhen small pockets of air or water are trapped against the forms. Achange in the mixture to make it less “sticky” or the use of small vibratorsworked near the form has been used to help eliminate surface air voids.Honeycombing can be reduced by inserting the vibrator more frequently,inserting the vibrator as closely as possible to the form face withouttouching the form, and slower withdrawal of the vibrator. Obviously, anyor all of these defects make it much easier for any damage-causingmechanism to initiate deterioration of the concrete. Frequently, a fear of“overconsolidation” is used to justify a lack of effort in consolidating