Seepage in Dams
Seepage in Dams
(OP)
I am assigned to design a small dam: 10 mts high and about 70 mts long.
Other than slope stability analysis, I understand I need to run a seepage analysis.
I have been wondering when seepage values are too small or too high for this small dam?
Are there any boundaries?
Other than slope stability analysis, I understand I need to run a seepage analysis.
I have been wondering when seepage values are too small or too high for this small dam?
Are there any boundaries?





RE: Seepage in Dams
RE: Seepage in Dams
A seepage analysis can determine the hydrostatic uplift pressure under the downstream slope for use in your stability analysis and the seepage gradient at the toe to be sure the ground won't be heaved and/or boiling occur. The seepage quantity can be estimated to evaluate water loss.
This is a good learning opportunity for you, but you need an experienced dam engineer to check your work. There are a lot of pitfalls, and a failing dam is dangerous.
RE: Seepage in Dams
RE: Seepage in Dams
I've been meaning to ask, are you from the town of Eolian TX? I never knew there was such a place until I saw it on the map while looking for Breckenridge. Does the wind blow a lot there?
RE: Seepage in Dams
For an embankment dam (i.e., with an unbound phreatic surface), the construction of a flow net is a touch difficult. I have successfully used numerical modeling (i.e., Modflow 3-d) to solve the quantity problem. You can consider the confocal parabala solutions for a back-of-the-envelope approach. The confocal parabola is really an approximation and best applied on a homogeneous dam design.
Solving flow problems to address the critical gradient is usually the bigger engineering concern. I usually would have internal drainage design to address critical gradient issues.
f-d
¡papá gordo ain’t no madre flaca!
RE: Seepage in Dams
RE: Seepage in Dams
RE: Seepage in Dams
I didn't know Eolian, TX was there. I looked on Google Earth, and I don't think you could call it a town nowadays.
I would guess that the wind blows a lot there. Take Google Earth to the Sweetwater area and see all the wind turbines just east of town.
I agree that a chimney drain is a good feature, although we seldom see one in a 35-foot high dam. A toe drain in a trench can be OK if you have a creek channel to spill into. If the soil is very sandy, a dam with no formal drain usually results in a marsh at the toe.
RE: Seepage in Dams
Maybe against the total aquifer capacity?. So if for example, my aquifer is 35000 gallons as total vol capacity, it means that only from seeping action, the aquifer will be filled in around 100 mins?, which might be too fast, considering all the utilities that need to evacuate (assuming this is the case).
Therefore in this case the seepage value is too high.
I haven't found a straight answer of this and text books don't provide this very clear answer. If anyone can provide any input, it is appreciated.
RE: Seepage in Dams
you need to calculate the exit gradient of your seepage to determine if the toe of the dam will blow out and fail.
you need to calculate slope stability with your assumed phreatic surface
you need to estimate the hyd conductivity to analyze if the reservoir will hold water
you need to evaluate the abutment and foundation to see if water flows in and through them
RE: Seepage in Dams
Internal erosion causes about half of all embankment dam failures. (Spillways cause about half, by inadequate capacity or poor design causing erosion in bad places, which leaves a very small fraction from all other causes like slope instability or earthquake.)
RE: Seepage in Dams
RE: Seepage in Dams
Unless it is justified to do numerical modelling as suggested by fattdad, which still going to depend on the reliability the parameters used on your model.