Design of Gravity/Hollow Gravity Dam 2

[gemeda]

Dear Sirs,

I am designing a small dam for an irrigation project in Ethiopia.At the selected dam site,the valley is V-shaped with 240m wide at the top and maximum depth of 67.5m.The foundation consists of sound rock overlain by shallow/colluvium deposits.Both the right and left abutments at the dam site are very steep with average slope of 1V:1.7H and there is no saddle in the area.

Question;

Is there any possiblity to use embakment dam for this project?


Thank You,

 

[cvg]

what will you use for the fill material? do you have a borrow source nearby that is suitable for a zoned earthfill embankment? The amount of fill will be large and maybe concrete will be cheaper. Where will your spillway be located? over the embankment? how will you divert the stream? You will need to do preliminary designs and estimate the cost and feasibility of these items. It all comes down to construction economics.

 

[msquared48]

At over two hundred feet high, I'd be very cautious, very, very cautious.

I would have to ask - should the dam breach, which is more probable with an earthen dam as opposed to a concrete gravity system, what would be the downstream social and economic impact?

Mike McCann
MMC Engineering

 

[gemeda]

cvg,

Thank you for your comment.The feasibility study is already conducted and a rock fill dam is found much cheaper.However,the steep topography at the right and left abutment creates difficulty for provission of separate spillway.What do you suggest if the spillway is made to partly run over the dam body at the right or left abutment?

 

[GeoPaveTraffic]

This is a large dam and needs to be engineered by people with considerable dam design experience. There are multiple dam and spillway configuations that might be possible, but will depend on the the geology, local materials, storm paterns, water shed size, etc.

 

[cvg]

spillways over an embankment dam are generally discouraged. you might consider facing the dam with RCC to allow overtopping. However, this will be very expensive. Additionally, design of the spillway should be an integral part of the feasiblilty study and may make the rock fill option less desirable when you find out how much it will cost to protect the dam from overtopping. Spillway requirements can also be greatly affected by the height of the dam and the amount of freeboard as well as by changing your operating rules. you can maybe reduce the size of the spillway by making the dam taller or by increasing the amount of freeboard (by reducing the elevation of the normal operating pool).

 

[msquared48]

You could make a gravity section with a spillway partway and fill in the rest with the earthen structure.

Mike McCann
MMC Engineering

 

[GoldDredger]

I have no practical experience in dam building but a few thoughts come to mind.

First is what geopave up there wrote, in that this is a considerable project, not just a small water reservior for a tiny community. This should be designed by an engineer(s) with considerable experience in dam building. Forgive me for saying, but not by an engineer who would need to post a question about dam design on this site.

That being said, in a gorge situation like this, with solid sides, I would be concerned how the embankment interacts with the sides. Seems like there would be potential for water migrating (and eroding) at the interface between solid rock sides and embankment.

 

[gemeda]

GoldDredger,

Your concern is correct.However,i dont see the danger of posting a problem for free discussion.Here ,its professionals who are discussing,and I think we are in the process of learning.Appologize if I miss your point.

 

[cvg]

it is recommended that all dams (embankment or concrete) be founded against rock at the base and at the abutments. The abutment contact areas are always of concern for seepage, piping and internal erosion. This is something that can be addressed with proper design and construction plans. That said, I agree that design and construction of dams is a very high risk business and should be done by a team of experts. I know of very few dam engineers (no pun intended) that would do it by themselves.

 

[twopie56]

Gemeda,

Good Topic you raised here,I am surely interested on all
the comments and advice they will give you.
I for one had experiences on Hydro Dams built in the Southeast.
I can say that you are on the early stage of the feaseble study.
Good luck on this project of yours i'll be checking on this topic and the possibility of embankment type for this situation and i'm excited to know that it could be possible, someone out here for sure is a master in this.

 

[Apakrat]

Contact the U.S. Bureau of Reclamation, Golden, Colorado for design criteria listing Your known info. They have similar completed projects on file.

Re: earth fill versus concrete structure. Erosion can be re-filled but usually concrete cracks are a &#x%

Re: earth fill abutting existing. Grout Cap, Grout Cap, Grout Cap.

Last but not least. With reference tools,it takes one imaginative person a little time to prepare a design that takes a team of engineers much longer to approve and then paying a contractor $$$ to see if it works properly!!!

My earth fiill dam foot prints--------
335 ft high X ~1.5 miles, Canadian River, Sanford, Texas
165 ft high X ~ 0.5 miles, Book Cliffs, Rifle, Colorado
185 ft high X ~ 1.5 miles, Colosseum Mine, Clark Mountain, Ca​

At 74th year working on IR-One2 - - UHK PhD - - -