Dynamic viscoelastic characterization of wooden foundation piles embedded in oxygen-depleted soils using individual annual-ring specimens

Abstract Assessing the deterioration of wooden piles embedded in anaerobic environments is challenging, as any changes in the density of the piles proceed very slowly. This study aimed to assess deterioration at an ultra-early stage, such that no significant reduction in density could be observed and the cell wall of the piles exhibited quite minimal deterioration. The deterioration this stage was evaluated by dynamic mechanical analysis (DMA), which is a useful tool for inferring the structure of lignin and the influence of the hemicellulose that interacts with it. Fourier transform infrared (FTIR) analysis and microscopic observations were also performed to support the DMA results. The storage modulus ( E' ) varied with density across the log’s cross section. However, the decrease in E' in the outer region of the log was minimal, which made it difficult to evaluate the extent of deterioration from this parameter alone. In contrast, the peak temperature of loss tangent (tan δ ) showed a tendency to be higher in the outermost region of the piles. Because the peak temperature of tan δ typically decreases when lignin is degraded, the result that the outermost region showed higher values than the inner region suggests that the lignin structure in the cell walls was largely preserved. The elevation in peak temperature of tan δ is attributed to the decomposition of hemicellulose, which is consistent with the FTIR results indicating degradation of polysaccharides and the microscopic observations showing localized cell-wall deterioration. These findings demonstrate that DMA provides a sensitive and effective means of detecting deterioration in wood at an ultra-early stage under anaerobic conditions, whereas conventional methods, such as density measurements, may fail to reveal significant changes.