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[Ferno]

Hello,

I always wanted to know how dams can hold an entire lake or sea without cracking. What I know is that it has something to do with the shape, but many different shapes of dams can be observed?

[webmaster]

Hello Ferno,

You are on the right way when talking about shapes.

A dam can have different shapes and can be built out of different materials.

For non-engineers to understand how a dam is withstanding the water pressure is difficult but can be explained as follows:

Common point for all dams: Good and impermeable foundation material required.

Gravity dams like the famous Three Gorges Dam in China withstand the water pressure due to their own weight being that huge that the dam can neither be pushed out of its foundations nor be turned around.
"The water pressure is directly absorbed by dam itself"
The usual triangular type of shape (thin top and fat bottom) is given to minimise the quantity of material as the top of the dam receives no pressure from the water. Further optimising of the shape is only for commercial aspect when as an example one wants to integrate the power generation inside the dam body. The concrete dam is constructed in seperate independent blocks, the concrete is not steel reinforced. So called vertical waterstops are built between the blocks to prevent the lake water from escaping.
This type of dam can be constructed using other materials such as selected earth, rock, or in composition with concrete.

Arch dams are usually more cost effective than gravity dams due to their thiner shape but are restricted to very good foundation properties such as hard rock and can obviously only be made out of concrete. The dam curved shape is calculated so that the water pressure is diverted towards the foundations.
"The water pressure is diverted through the dam and absorbed by the foundations".
Here also, construction in blocks is carried out but blocks are not independent, as block contact is needed to divert the water pressure to the foundation.

Other dams shapes are generally a combination of the above depending on foundation properties, materials availabilities and budget.

Hope the answer is of help to you.

[Ferno]

Thanks for the info.

Could you advise where I could find a book with nice pictures of arch dams.

Ferno

[webmaster]

The best book you can have about dams is supplied by the International Commission on Large Dams and is called: "World Register of Dams"
This book is filled with great pictures and technical data on all large dams worldwide, curved, gravity, earth dams, etc.

This book can be ordered here: http://www.icold-cigb.net/listepublications.aspx#reg