Testing mechanical characteristics of chestnut stakes used in bed sills for stream restoration

Using of wood elements for constructing bed sills in Mediterranean streams, where the banks are not protected by tree vegetation, needs an evaluation of biological and mechanical characteristics for evaluating both the wood durability and the effectiveness of the stream restoration project. Very few studies have dealt both with the decay of mechanical characteristics of wood elements employed for stream restoration works and with the changes over time of physical and chemical wood characters. In this paper, for a wood and stone bed sill located in a stream having no shaded banks, the changes of physical and chemical characters detected after 12, 18, 24, 30, 36, 42 and 48 months on chestnut stakes are preliminarily recalled. Then, using three chestnut stakes extracted after 96 and 108 months and two unaltered stakes, as reference condition, the mechanical compression tests were carried out. The results of the compression tests for both runs (altered and unaltered stake) allowed to establish the influence of the ageing process on the compressive strength and stiffness of the chestnut wood. Finally, using two chestnut stake extracted after 108 and 120 months and two unaltered stakes, the flexural tests were carried out by a four points scheme (two supporting points and two loading points) according to UNI EN 408-2012 standard. The results of the flexural tests for both runs (altered and unaltered stake) allowed to establish that the wood ageing process determines the decay of mechanical strength of the material and reduces the bending strength of the chestnut wood. From an applicative point of view, the obtained results showed that after 10 years the mechanical resistance characteristics of the wood stakes are less than those corresponding to the undisturbed reference condition