Bacterial decay in wooden foundation piles—Patterns and causes: A study of historical pile foundations in the Netherlands

Many wooden foundations under historical buildings in the Netherlands are affected or threatened by bacterial degradation. This study provides some fundamental information for: (1) classification of the degree of degradation in relevant hardwood and softwood species by evaluating wood anatomical characteristics; (2) assessment of the degree of bacterial degradation in wooden foundation piles across pile diameters, and vertically, along the piles for an inventory; and (3) determination of the effect of the degree of bacterial degradation and specific wood technological parameters on the wood piles. The aim is to get a better understanding of those parameters that affect the degree of degradation. Based on observations from more than 2000 piles, different patterns of degradation across and along the piles are studied, and a simple model is presented to predict compression strength from the moisture content of increment cores taken from the pile head. With this model, it became possible to calculate whether a pile foundation in service is stable enough to remain in place and function as a support. A hypothesis is presented on water movement in the piles, which is identified as a key factor that stimulates bacterial wood degradation.