Technical Inspection
From ASDSO Dam Safety Toolbox
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- “A visual inspection is hands-on and requires careful and close examination. The inspector should look closely at the members of connections and not just view them from a distance. Inspectors should use various measuring scales, and other hand tool to identify, measure, and locate areas of concerns. Boroscopes, flashlights, and mirrors bay be necessary to inspect areas of limited visibility. Weld gauges should be available to check the dimensions of weld beads. Critical areas should be cleaned prior to inspection, and additional lighting should be used when necessary”.[1]
- “It is important to look at the entire surface area of an embankment. The general technique is to walk over the slopes and crest as many times as is necessary in order to see the entire surface area clearly. From a given point on the dam, small details can usually be seen for a distance of perhaps 10 to 30 feet (3 to 10 meters) in any direction, depending on the roughness of the surface, vegetation, or other surface conditions. Therefore, to ensure that the entire surface of a dam has been covered, several passes must be made. It is not really that important what approach is used, as long as it is systematic such that all of the surface area is covered.[2]
- “At regular intervals while walking the slope and crest of a dam, an inspector should stop and look around in all directions to: observe the surface from a different perspective, which sometimes reveals a deficiency that might otherwise go undetected; check the alignment of the surface. In addition, viewing the slope from a distance may also reveal a number of anomalies such as distortions of the embankment surfaces and subtle changes in vegetation. Often these types of observations are not apparent when viewing them close up.[2]
- “The areas where the embankment contacts the abutments (sometimes referred to as the groins) should be inspected carefully. Inspection of the groins is important because: these areas are susceptible to surface runoff erosion; seepage often appears along the groins because the embankment/abutment contacts are more susceptible to seepage. When checking the alignment of the crest of a straight-axis dam, as well as any berms on the upstream and downstream slopes, an inspector should center his/her eyes along each shoulder of the crest or berm and move from side to side in order to view this line from several angles.[2]
- “Some tools or techniques that are helpful in sighting are: binoculars and telephoto lens: the use of binoculars or a telephoto lens can help in observing misalignments because distances are foreshortened and distortions perpendicular to the line of sight become more apparent. Reference lines: the use of a reference line can also be of great assistance in sighting. Reference lines can be existing features such as guardrails, a row of posts, pavement stripes on a roadway on the crest of the dam, parapet walls, etc.[2]
- “The sighting techniques described above are also useful for detecting a change in the uniformity of embankment slopes. The contact between the reservoir waterline and the upstream slope should parallel the alignment of the dam axis. In other words, the reservoir waterline should be a straight line if the dam has a straight axis.[2]
- “The alignment of the slope at the waterline can be checked by standing at one end of the dam and sighting along the waterline. Non-linearity of the waterline may indicate erosion or movement of the slope.[2]
Citations:
Revision ID: 6543
Revision Date: 02/21/2023