Belled piles (otherwise known as under reamed piles) have mechanically formed enlarged bases in the form of an inverted cone, and can only be formed in stable soil conditions. They are a useful method for increasing the bearing capacity in deep foundations, and allow a greater bearing capacity than a straight-shaft pile.
These piles are appropriate for wide ranging soils which are often subjected to seasonal moisture differences, filled up ground and detached or soft strata, as well as being used in common ground conditions where economics are favourable due to the reduced pile shaft diameter (requiring less concrete).
Red Deep Piling has Belling tools that range from 500mm to 4700mm.