The galleries located inside the Hoover dam are pretty amazing, right? Are they used for inspection purposes? Well they are responsible for draining water from beneath the dam body as shown.
Fig. 1 : Galleries drain water from under the dam body.
If these seemingly simple galleries were missing from the structure design, what would happen? The seepage water would flow freely. If water seepage flows the way shown above there would be devastating consequences for the dam as shown.
Fig. 2 : Damaging effects of the dam.
A Small Experiment
I did a small experiment to test this. I created a basic dam like structure in the soil as depicted below. This dam stands strong within the soil and then I added water to observe the outcome.
Fig. 3 : Dam within the soil and adding water.
When I release my hand the dam just lifts up as shown below.
Fig. 4 : Releasing of the hand and dam uplifts caused by water seepage.
The Concept of Uplift Force
When water level at upstream and downstream are different, seepage water flows below the dam body. Seepage water is very difficult to control and it happens due to the pressure differential. The seepage water exerts an upward force on the dam body. This is known as uplift force. Uplift force causes a huge instability to the dam. This is the reason the dam got lifted up from its original position in the experiment.
Fig. 5 : Uplift force causes uplift in the dam.
In a gigantic dam like Hoover dam, such untreated uplift force may not topple the dam instantly, but over time it can lead to crack and instability of the dam.
Reducing the Uplift force with the help of inspection galleries
This is why they gave provision for the drainage or inspection galleries during concreting of the dam. How can they reduce uplift force? That’s the duty of drainage holes which are shown in the image below.
Fig. 6 : Inspection galleries help to reduce uplift force.
These grout-filled holes suck seepage water from the dam’s foundation and greatly relieve the uplift pressure. This obviously reduces the uplift force.
Fig. 7 : Grout holes drain seepage from the dam's foundation.
The collected water is eventually pumped out downstream as shown below.
Fig. 8 : The collected water is pumped downstream.
These galleries are also used for inspection. It is amazing to know how such simple technologies provide great stability to the dam.
That's all for this article. I hope you get a clear understanding why the inspection galleries are the life saviour of this giant structure. Thanks for reading.
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