Forest Road Pavement Design in New Zealand

The New Zealand forest industry currently has an annual cut of 19 million m 3 that is expected to increase over the next decade to 30 million m 3 per year. Much of the new production is situated in first-rotation forests that are located on steep terrain and have minimal existing forest road networks. A survey conducted as part of this study identified that current road engineering practices vary widely between forest owners and that forest road construction owes more to the experience of roading supervisors than to formal design methods, qualifications and training. While the economical design of forest roads is affected by many factors, including: road location and surveying, geometric design, and construction and maintenance, the acquisition and placement of aggregates for pavement can contribute 60-70% of forest road cost. The majority of forest owners use a single „improved‟ aggregate layer to complete their forest road, as opposed to a multi-layered approach used for most public roads. This paper focuses on reviewing the aggregate grading standards available for forest road design, and notes there is considerable variation between standards. A series of eight aggregates actually used for East Cape forest road construction were analysed by sieve test and compared to the standards. It found that the aggregates had widely varied gradation and were dissimilar to the gradation envelopes of the reviewed standards. Further research is required to determine an aggregate grading standard that will best suit East Cape aggregate sources and conditions. Background The New Zealand commercial forest estate is currently estimated at 1.8 million hectares, with an annual cut of 19 million m 3 (MAF 2008). The annual harvest is predicted to increase by 50% over the next decade (MAF 2000). Much of this new harvest area is situated in first-rotation forests that are located on steep terrain and have minimal existing forest road networks. A significant investment in forest road design and construction is required in order to provide access for harvesting in these new areas. This investment will call for the application of sound technical engineering knowledge and capability. Anecdotal evidence obtained through discussions with forest managers has identified that forest road engineering practices vary widely across the industry, and that many forestry regions struggle with developing and maintaining a cost-effective forest road network. The current level of forest road engineering capability in New Zealand, and the specific nature of deficiencies, is not well understood.