When seepage takes place through the body of an earthen dam, it leads to
The most preferred soil for the central impervious core of a zoned embankment type of an earthen dam, is
Zoned embankments are usually provided with a central impervious core, covered by a comparatively pervious transition zone, which is finally surrounded by a much more pervious outer zone. Clay inspite of it being highly impervious, may not make the best case, if it shrinks and swells too much. Due to this reason, clay is mixed with fine sand or fine gravel so as to use it as the most suitable material for the central impervious core.
During the construction of an earthen dam by hydraulic fill method, development of pore pressures become important in the
In hydraulic -fill method, the dam body is constructed by excavating and transporting soils by using water. Pipes called flumes, are laid along the outer edge of the embankment. Since the fall is saturated when placed, high pore pressure develop in the core material, and the stability of the dam must be checked.
The base width of a rock fill dam, incomparison to that of an earthen dam is:
Rockfill dams have characteristics lying somewhere between the characteristics of gravity dams and those of earthen dams. They are less flexible than earthen dams and more flexible, then gravity dams. Their foundation requirements are not a strict and rigid as are required for gravity dams. But the foundation requirements are more rigid than those for earthen dams which can be constructed almost on any types of foundations.
On moderate foundations, and particularly in seismic areas, the type of dam which can preferably be considered for construction, is
Rockfill dams are very useful in seismic regions, as they provide high resistance to seismic forces because of their flexible character
The centre of pressure of wave pressure due to wave of height hw acting on a gravity dam will be at a. height above the maximum still water level of
If the uplift pressure is neglected, the base width of an elementary profile of a gravity dam of height H, having relative density of the dam material = Sc, and coefficient of friction = μ is
Hence, if B is taken equal to or greater than no tension will be developed at the heel
with full reservoir.
When, C = 1
If uplift is not considered,
For the dam to be safe in sliding,
If C = 0, i.e., no uplift is considered then,
If full uplift pressure is considered, the base width of an elementary profile of a gravity dam of height H with relative density of dam material = Sc and coefficient of friction = μ is
The limiting height of a low gravity dam of elementary profile neglecting uplift conditions
If fc represents the allowable stress of the dam material, then the maximum height (Hmax) which can be obtained, without exceeding the allowable compressive stresses is given as:
For the upstream slope of an earth dam the most critical condition is