This paper presents the results of a research project to determine the long-term performance of wood fibre embankments, that were constructed by the Washington State Department of Transportation (WSDOT) beginning in 1972. At the time of their construction, concern existed that wood fibre fills would only provide a 15 to 20 year service life.
Performance of existing wood fibre fills was evaluated based on the quality of the wood fibre material, quality of the effluent, and condition of the pavement. A visual classification system rating the wood fibre from fresh to completely decomposed was developed and used in order to establish a criteria from which all wood fibre material could be rated. Visual examination in conjunction with laboratory tests were used as determining aspects for the effluent quality. The WSDOT Pavement Management System was used to evaluate relative pavement performance. Site descriptions are presented giving specific characteristics and properties of the fills inventoried. An analysis of this information was done to determine the effectiveness of the fills.
Over half the wood fibre samples were found to be nearly fresh or fresh and none were found to be completely decomposed. In all but one case, the pavement quality over the wood fibre fills surpassed the comparative highway segment rating indicating the wood fill's performance exceeded that of the surrounding area. Generally, the surface water in the vicinity of the wood fibre was found to be clean and pure indicating no adverse impact of effluent. Given the above findings, embankments constructed of wood fibre were found to perform well over almost a 20 year period. Service life in excess of 50 years can be expected of wood fibre fills.