First Filling and Monitoring

"If an embankment dam were to fail under conditions that could be appropriately defined by a limit-equilibrium analysis, it would do so at one of three critical periods... during construction... first filling... [and] achievement of maximum pore pressure under a full reservoir."^[1]

"The second critical period is the first filling of the reservoir. If the dam survives the initial filling and if there is no blowup at the toe, the dam can be considered safe (in effect proof-tested) against failure by piping due to heave... Under many circumstances, including the presence of relatively thin cores or ample well-drained downstream shells, pore-pressure maxima follow so rapidly after the first filling that the survival of the first filling can be considered to be a demonstration of the ultimate safety of the dam under full-reservoir conditions. However, if the impervious section of the dam is thick and impermeable enough to create a time lag between the rise of the reservoir and the rise of piezometric levels in the core or supporting downstream zones, pore-pressure equilibrium may not occur for several years after the reservoir is first filled and the critical period may be delayed."^[1]

"The factor of safety of a dam that survives its first filling and the associated increases in pore pressure will increase with time, unless this factor of safety is so close to unity that cyclic loading produced by fluctuations in the level of the pool causes strain softening and a critical loss of strength."^[1]

"Some very loose sand foundations may also be collapsible under static loading. They sustain the load from construction of the embankment and then, during wetting or saturation during reservoir filling, they consolidate rapidly or 'collapse.' These types of foundation soils must be identified and accounted for in the design."^[2]

"Experience has shown that dumped rockfill dams often settle and deflect downstream significantly during initial filling. Consequently, many of these high lift embankments have developed leakage problems, and experience has indicated that rock material placed in thin lifts (1 to 4 feet thick) and compacted by vibratory rollers provides a more stable mass in which settlement is minimal."^[2]