How does a concrete gravity dam resist the pressure of reservoir water?

A concrete gravity dam, such as the Three Gorges Dam, is specifically proportioned to resist the horizontal thrust of reservoir water primarily through its own massive weight.12

By relying on its substantial mass, the structure prevents overturning and sliding forces. The stability of the dam is maintained by the balance of three primary forces: the horizontal thrust of the stored water, the weight of the dam itself, and the pressure exerted by the foundation. In addition to its weight, the dam utilizes the inclined reaction of its foundation to counteract the water's pressure.12

Engineers must also account for other factors that could destabilize the structure, such as buoyant uplift from water seeping beneath the dam, seismic activity, and pressure from silt or ice. To manage these risks, designers often incorporate systems like grouting to seal fissured rock and drainage mechanisms to relieve uplift pressure. While gravity dams are typically constructed of unreinforced concrete, they can be further strengthened using posttensioned steel rods anchored into the foundation to resist overturning tendencies.1