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Pier Redundancy

A typical ABC pier can be built with two precast columns tied to concrete drilled shafts (or forget the precast columns and use the drilled shafts as the columns). Then tie the precast pier cap to the columns.

Of course this type of pier is only useful on land. The pier columns are typically not suitable for river environments because of ice and water loads. Also this type of frame pier suffers from non-redundancy (is that a word?). Meaning if one of the drilled shafts settles or gets hit by a vehicle the whole pier could fall down.

For this reason most DOTs like the idea of pile foundations.

Because the chances of multiple piles failing is rare.