ABSTRACT
Historical Venetian buildings were commonly founded on top of wooden planks lying on small in both diameter and length wooden piles, embedded at a very modest depth.
The purpose of small wooden piles is to improve the mechanical behavior of the soft clayey silt, which characterizes the shallowest layer of the Venice lagoon, thereby reducing expected settlements. Since the piles are short and tightly spaced, the load-bearing capacity of the foundation does not increase significantly; moreover, the piles rarely reach stiffer layers of the soil.
Wooden piles were long believed to last indefinitely, as they are permanently waterlogged.
Recent evidence has however disproven this assumption, showing that anoxic bacteria can seriously deteriorate wood even in anoxic conditions.
The effects of wood deterioration on the mechanical behavior of the foundation over time are modeled by numerical analysis, showing that wood degradation leads to stress transferring from the piles to the soil, causing an increase in settlements. This effect is more severe if not only the outer piles of the foundation are deteriorated but also the entire group of piles.
