Question

a wall of dam is broad as it's base

Answer 1

A thicker wall is required to with stand greater pressure, therefore, the thickness of the dam increases towards the bottom.

Answer 2

The wall of a dam is broad at its base. The reason behind this is, pressure exerted by the liquid increases with increase in depth.

The dam contains huge amount of water and as we go deep the pressure exerted by such a huge amount of water increases to very high.

In order to release this pressure the area of contact must me more and hence the walls are made broad at its base.