Introduction
The New Zealand Forest Road Engineering Manual covers all aspects of planning, design, construction and maintenance of unsealed forest roads. It is a detailed guide for those who have a limited engineering background, as well as a reference for more experienced forest roading supervisors and engineers. The best road construction results will be achieved by the application of technical information combined with knowledge and experience. Manual users are encouraged to seek out and draw upon the knowledge of experienced roading contractors, supervisors and engineers in the forest industry.
Building and maintaining forest infrastructure is a critical part of a successful and sustainable forest industry. In New Zealand’s plantation forest estate there is an estimated 25,000 km of existing forest roads and over 100,000 landings. As our commercial plantation forest continues its growth phase due to the extensive new plantings in the early 1990s, approximately 1500 km of new forest roads are being built each year.
While building and maintaining forest infrastructure results in an economic benefit by providing access for harvesting, it reduces the forested area by 4 per cent. Careful planning is critical in terms of managing road expense and maintaining environmental and safety standards. A road that meets environmental, safety and economic goals can be referred to as being ‘fit for purpose’.
Well-designed and built roads are safe, have a low environmental impact and are an asset to the forest landowner.This Manual is only one tool in a suite that has been developed to assist with planning and operational decision-making. It should be read in conjunction with other key references and planning documents. These include WorkSafe’s Approved Code of Practice for Safety and Health in Forest Operations, which provides detailed information on safe practice.
Planning for roads and landings is normally done as part of the broader harvest planning process. This is because the aim of forestry infrastructure is ultimately to provide suitable access at the appropriate service level for forestry operations.
A good planner has a broad skill set, uses a suite of available tools to assist decision-making, and preferably has a detailed knowledge of the area in which they are working.
A recent survey of forest road managers noted the challenge of building roads well in advance of harvesting – the ahead position – as is recommended best practice. Other challenges include putting together and managing an effective road lining crew that is efficient in harvesting and road building, keeping costs down, managing fair payment systems and dealing with cleanup operations after major storm events.
Roads and landings need to be appropriately located and built for the terrain they are crossing. Unless the forest is on easy country with few safety, environmental or social constraints, the task is often more complex than simply determining the location, width and alignment that gives the lowest combined cost for road construction, maintenance and haulage. By far the most cost-effective stability mitigation on logging roads is done at the planning stage – long before any machine reaches the road location.
Planning and field reconnaissance identify and mitigate potential construction and environmental issues, and a well-prepared paper plan ensures that field validation focuses on addressing issues rather than trying to identify them. It is a false economy to take shortcuts in these areas. Economic analysis may be a useful tool to assist in determining the viability of a construction programme. See 1.2 Economic analysis (Chapter 1).
High quality mapping is a good investment
Construction of forest roads and landings can produce significant environmental impacts. Planners need to ensure that laws, such as the Resource Management Act (RMA), regulations such as the National Environmental Standards for Plantation Forestry (NES-PF), and environmental rules and guidelines, such as those set by the NZ Forest Owners Association (FOA) are followed to minimise adverse effects.
Other FOA guides include the companion NZ Forest Road Engineering Manual Operators Guide, and the recently released suite of FOA Forest Practice Guides.
Road planning is often a trade-off between competing requirements. A common primary purpose of a new forest road is to link a proposed landing to the existing road network, because its position is critical in ensuring an efficient harvesting operation. However, it is not always possible to get a road to these locations. For example, there may be safety, environmental or economic constraints that restrict the selection of that option. The outcome is a trade-off where the landing position is changed, or an alternative harvesting system is used, for example, two-staging.
A key part of road planning includes the road specification, also commonly referred to as a road standard. Road standards depend primarily on the expected level of use, and have a required width, maximum grade, curve radius and other factors to ensure they are fit for purpose.
However, most forest roads will also need to transport non-standard vehicles such as haulers, transporters, off-highway logging trucks, stem trucks or trucks with increased weight and dimension, and will require special road geometry and pavement design to accommodate them. These vehicles often require greater road width, especially on curves to address off-tracking, and greater pavement depths to carry higher axle loads. Also, over the last five years high productivity motor vehicles (HPMV) have become increasingly used as more highways have been opened for use by these vehicles. Many logging trucks are 50 Max, which is a class of HPMV. The vehicle combinations have one more axle than conventional 44-tonne vehicles, so the overall truck load is spread over more wheels.
Navigating around the Manual
The Manual’s goal is to provide a detailed overview of the forest engineering process – from planning, field layout and construction to maintaining the asset. It is not a linear process because building even a small forest road may have challenges. As already mentioned, infrastructure design and build are complex and typically require many elements to be considered that may differ from site to site. The Manual also provides a brief summary of relevant regulations and other statutory requirements.
Chapter 1 introduces forest road engineering terminology and two elements critical to effective infrastructure design and build – economic analysis and risk management.
Chapter 2 covers consents and compliance. For all earthwork projects it is critical to be aware of legal requirements — planning, construction and maintenance must comply with them. Depending on the site and scale of the project, operations may require permission (a ‘consent’). This chapter provides an overview of the relevant legislation or regulations, describes where this information can be found and highlights the typical processes to follow.
Chapter 3 provides a step-by-step approach to designing the forest road. This includes determining the type of map resources available, preparing a paper plan and undertaking field investigations, through to laying out a fully designed road in a forest.
Chapter 4 provides an overview of landing design. While most of the Manual focusses on forest roads, landings are an integral part of forest infrastructure. This chapter does not discuss broader planning construction processes that are the same as for roads.
Chapter 5 describes road and landing construction from a planning and operational perspective. It provides information on both technique and equipment options.
Chapter 6 is about the road pavement. It covers the testing of the subgrade (parent material) on which the road will be built, calculating traffic loading, designing pavement thickness, and options for stabilising a weak subgrade.
Chapter 7 discusses erosion, sediment and slash control structures. It is essential that water is dispersed and at times treated. These are regulatory requirements. This chapter describes ways to reduce environmental impact and maintain the integrity and longevity of the infrastructure through erosion and sediment control.
Chapter 8 provides different options for getting across rivers, the importance of maintaining fish passage, and includes technical information on some of the structures. For example, how to calculate culvert dimensions.
Chapter 9 highlights the importance of maintenance, not just to ensure the roads stay open for the intended truck traffic, but also the importance of protecting the infrastructure investment.