FGR assisted Hamish Scown of Pan Pac Forest Products Ltd with recent trials of using shredded wood from forestry debris as temporary roading aggregate. Three test roads were built using shredded wood in layers half a metre deep (500mm) to see how it would stand up to heavy logging truck traffic. Initial results have shown that shredded wood can work surprisingly well as a temporary road surface.
The initial trials proved successful with initial traction issues on steep grades when laid uncompacted, but compaction by heavy traffic or roller after laying alleviated the initial traction issues. Wheel rut depths were measured at specific log truck pass frequencies, and it was found compaction occurs primarily within the first 20 vehicle passes and then slowly increased to a much more stable and stiffer road surface over time. Rehabilitation of the roads was much easier and cheaper than a metalled road especially during the winter as the roads were permeable and able to diffuse water, reduce sedimentation and runoff, and resist mud punching.
The trial also investigated using 65mm crushed and 100mm crushed aggregate as a running coat on two of the roads and it was found that 100mm crushed performed better for aiding traction. Road metal punched down enough to embed in the wood and provide a denser more stable interlocked road, while providing traction after wheel ruts on steep grades got too slippery from wear and introduction of mud after rainfall. Traction during rain events was satisfactory. Design elements to reduce mud being carried onto the running surface such as enough “running in” distance over flat ground with shredded wood prior to steeper grades worked effectively.
Fig 2: Joule Rd. Mohaka Bridge Block – Pan Pac Forest Products Ltd. Final preparatory work shaping ‘metalled’ road at 500mm depth of shredded wood. Grade was 11.5% off landing with no run up.
During the trials, Pan Pac Forest Products hosted a field trip for about 50 industry engineering, harvesting, and environmental staff. The visit sparked strong interest, and the approach has since been picked up by several forest management companies across the country as a practical way to address both high costs of aggregate and surplus woody residues.
The trials showed the importance of construction methods. Roller compaction made a clear difference, and Phase Two of the study will test roller compaction, shred depths, and the use of geotextiles to improve drainage. The next round of work aims to refine the technique and find the best balance between cost, durability, and ease of use. The approach offers a sustainable way to turn harvesting residues into a useful roading material, helping forestry operations reduce cost while easing the demand for roading aggregate, which is a scarce resource in some forests.
For more information contact: Mr Hamish Scown, Operations Technical Co-ordinator, Pan Pac Forest Products Ltd, m: +64 27 878 4630, e: Hamish.Scown@panpac.co.nz
