Foundation piles: analysis of beech wood decay in service life conditions
Q Kleindienst, A Besserer, M-L Antoine, C Perrin, J-F Bocquet, L Bléron
Wood piles foundation system was largely used over decades. Thus, numerous buildings over the world are based on this constructive system. In the context of reduction of CO2 emissions in the building field of constructions, substitution of concrete by wood as material for foundation piles seems to be a promising alternative. However, fluctuation of the water table level in soil may promote fungal decay of the wood foundation piles in service. Thus, wood used as foundation pile was often treated with high toxicity chemical products. To promote the use of wood in pile foundation on the basis on its natural durability, diagnostic and prediction methodology of the wood decay needed to be improved. Mesocosm decaying experiments were carried out on beech wood mini-stakes. Influence of a water gradient occurring in wood on its strength loss was evaluated. Compression parallel to the grain (fc,o), fungal colonization of wood, near infrared spectroscopy and enzymatic activities measurements were used to decipher wood decay. However, none of these factors was fully accurate when considered alone. Indeed, degradation pattern seemed to be patchy due to high heterogeneity of the wood and repartition of microorganisms in soil. It turned out that no optimal correlation could be found after an one factor analysis. At the contrary, multivariate analysis allowed an accurate clustering of the wood samples. This approach discriminated between samples with identical fc,o value but that differed by their enzymatic activities and cell wall polymer contents. Finally, a predictive model of the fc,o was built. The model had the potential to predict the fc,o of a wood foundation pile from on-site measurements. Relative part of the enzymatic activity in the wood decay dynamic is also discussed.