Forest Road Pavement Design in New Zealand

Abstract

The New Zealand forest industry currently has an annual cut of 19 million m3 that is expected to increase over the next decade to 30 million m3 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.