How can water seeping beneath a gravity dam create uplift pressure?

Uplift pressure in a gravity dam occurs when water from the reservoir seeps beneath the dam’s base or into its horizontal joints. Because gravity dams rely on their own weight to resist the horizontal thrust of retained water, this seeping water exerts a buoyant upward force that can destabilize the structure.12

This phenomenon is a critical concern for engineers, particularly because rock foundations are often permeable to varying depths, making it difficult to create a perfectly impermeable seal. To manage these pressures, engineers employ several strategies:12

• Cutoffs: A downward projection of concrete into the rock foundation or the use of grouting to seal fissured rock can help block seepage paths.12
• Underdrainage: Drainage systems are installed to relieve the buildup of pore water pressure by safely channeling seepage away from the base of the dam.12

Many modern gravity dams utilize a combination of these methods to ensure structural integrity against the destabilizing effects of uplift.12