Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 9—Inspection and Assessment of Conduit-Related ProblemsAn instrumentation program should involve instruments and evaluation methodsthat are as simple and straightforward as the project and situation will allow.Instruments selected for use should be accurate, precise, and provide forrepeatability of measurements. Beyond that, the designer and embankment damowner should make a definite commitment to an ongoing monitoring program. Ifnot, the installation of instruments will probably be wasted. Increased knowledge ofany deficiency and emergency condition of the embankment dam acquired throughan instrumentation and monitoring program is extremely useful in determining thecause of the deficiency, the necessary or probable remedy, and monitoring duringand following corrective actions. Involvement of qualified personnel in the design,installation, monitoring, and evaluation of an instrumentation system is of primeimportance to developing and achieving a successful and meaningful instrumentationand monitoring program.A wide variety of devices and procedures are available for use in monitoring thebehavior of and deficiencies along a conduit and at an embankment dam. Table 9.1provides a listing of potential deficiencies and conditions and their causes that couldbe encountered along the alignment of a conduit. The table also provides a briefdescription of where the condition could be encountered and the instrumentationthat could be used to monitor the condition. Additional discussion of eachmeasurement is provided in the following sections. Most of these measurements aretypically done for embankment dam concerns. However, there is some applicabilityto conduits. Further information or instrumentation and monitoring is available onASCE’s Guidelines for Instrumentation and Measurements for Monitoring Dam Performance(2000).9.8.1 Structural deformationStructural deformation of a conduit could lead to crack development or jointsopening up along the alignment of the conduit. These deficiencies could result inthe potential for internal erosion or backward erosion piping of embankment dammaterials into or along the exterior of the outlet conduit. In the case of waterseeping into the conduit through open joints or cracks, an unprotected exit point forthe seepage exists, which could allow for the internal erosion or backward erosionpiping of embankment dam materials into the conduit. For pressurized conduits,open joints or cracks in the conduit could allow for the saturation of theembankment dam materials around the conduit under a high seepage gradientcondition, which could also lead to the internal erosion or backward erosion pipingof embankment materials. Structural deformations may result from foundationsettlement, lateral deformation of the embankment slopes above or below theconduit, or a collapse of the conduit due to a structural defect in the conduit orgrowth processes within concrete, usually resulting from alkali-aggregate reaction.235