Predicting the beech wood decay and strength loss in-ground

•A detailed analysis of beech wood decay in ground was performed.•Stochastic occurrence of fungi explained patchy wood degradation.•Wood strength was accurately predicted from NIR spectra performed on timber samples.•A multivariate model to predict wood strength and infer its service life is proposed.•The procedure is easily transposable to on-site measurements.

In the context of reduction of CO2 emissions and costs in the construction industry, substitution of concrete by wood for foundation piles seems to be a promising alternative. To promote the use of local wood in pile foundation, diagnostic and prediction methodology of wood decay in soil need to be improved. Outdoor mesocosm decay experiments were performed to evaluate the potential use of beech wood as foundation piles. The stochastic occurrence of soil fungal inoculum in contact with mini-stakes and water gradient in wood explained the observed patchy wood decay pattern. Various patterns of wood rotting fungi were identified. The correlation between measured strength loss and mass loss was weak. Multivariate analyses using biochemical and physico-chemical data as inputs allowed section categorizations and prediction of wood strength. Accuracy of the prediction was validated by experimental measurement of the compression parallel to the grain (fc,o). The categorization of unknown sections was computed by PLS-DA and provided clues inferring their service life. The described procedure has the potential to be transferred to on-site measurements to predict the fc,o of wood foundation pile or any potentially damaged timber structure.