In a buttress dam, the impounded water's weight is used to resist which forces?

In a buttress dam, the impounded water's weight is used to resist which forces?

• A. Lateral and vertical thrust as well as sliding at the base
• B. Sliding and overturning by its own weight
• C. Thrust from the water being held and stress at the base due the weight of the dam and the water
• D. Vertical strain and lateral thrust

Answer: (B)

The key idea is that stability against sliding and overturning in a buttress dam comes mainly from the dam’s own weight. The water behind the dam creates a strong horizontal hydrostatic thrust on the upstream face, which tends to push the structure downstream and overturn it. The vertical load provided by the dam’s mass increases the friction at the base and creates a restoring moment about the toe, helping to resist those horizontal and rotational tendencies. The impounded water’s weight does not act to resist these forces; in fact, the water’s pressure is what drives the need for resistance. So the buttress dam relies on its own weight (and the foundation reactions) to counter sliding and overturning.

The key idea is that stability against sliding and overturning in a buttress dam comes mainly from the dam’s own weight. The water behind the dam creates a strong horizontal hydrostatic thrust on the upstream face, which tends to push the structure downstream and overturn it. The vertical load provided by the dam’s mass increases the friction at the base and creates a restoring moment about the toe, helping to resist those horizontal and rotational tendencies. The impounded water’s weight does not act to resist these forces; in fact, the water’s pressure is what drives the need for resistance. So the buttress dam relies on its own weight (and the foundation reactions) to counter sliding and overturning.