Water flow through wooden foundation piles: A preliminary study

The process of bacterial wood degradation is not yet fully understood. From recent studies on foundation piles the assumption arose that water flow through wooden piles could be of crucial importance in explaining the intensity and velocity of bacterial decay. In a laboratory experiment we investigated the amount of water that passes through 300-mm-long fresh-cut stems of pine, spruce, larch, Douglas fir, alder, and oak over certain time intervals. The water pathways were traced by using a copper sulphate solution that was stained subsequently. A second laboratory experiment whereby different pressures were applied to the water was performed on spruce and pine only. In addition to axial water flow, radial water flow was also investigated. The results indicated striking differences between the six species. Douglas fir and larch proved to be almost impermeable, whereas huge variations between piles occurred in the other, more permeable species, namely in pine. In general, it became obvious that species that are known to be more susceptible to bacterial decay, such as alder, oak, and especially pine, appeared to be most permeable to water. The second experiment showed that axial water flow through pine and spruce is much—up to 100 times—faster than radial flow. By increasing the pressure in eight steps, up to 185 hPa, water flow increased linearly in both pine and spruce. The results of the two water-flow experiments are discussed in relation to observed patterns in bacterial degradation in the six species, with particular focus on spruce and pine, the most prominent species used in foundation piles. As water flow through foundation piles is strongly related to site hydrology, the impact of site hydrology on pile degradation is also discussed.