Robert A Douglas

Contact Pressures and Energies Beneath Soft Tires: Modeling Effects of Central Tire Inflation—Equipped Heavy-Truck Traffic on Road Surfaces

Much has been made of the use of tires with low-inflation-pressure systems called central tire inflation (CTI) systems. Great benefits have been noted in numerous trials, including the reduced requirement for truck maintenance, improved gradeability, longer tire life, improved ride for drivers, reduced road rutting, and reduced road maintenance. Reports of successful field trials in the literature are confirmed by other supporting theoretical studies. However, the studies reported in the literature tend to relate to unsealed, unbound roads. Given that in some quarters there is now a desire to extend the benefits of the use of CTI to sealed roads, new questions arise. A full-scale, laboratory study was carried out at the University of Ulster, Northern Ireland. Both the normal and shear contact stresses were measured with a high-speed data logger connected to electronic sensors in the apparatus’s bed plate, as a tire ran over them. Tire pressures and loads were varied in this factorial study. The contact stresses were measured, and conclusions based on their distribution across the tire “contact patch” were presented. In addition, contact energies were inferred, and the consequences for sealed pavements were suggested.

Appropriate Pavement Maintenance and Rehabilitation Management System for Local Governments

Local government officials find themselves squeezed between the need to produce pavement rehabilitation and maintenance budgets by using rational, systematic approaches and the lack of pavement engineering expertise and scarce funds. To meet that challenge, an appropriate pavement management system (PMS) is required. Such a system must be sufficiently sophisticated, yet straightforward and transparent in use. This paper outlines the development of a PMS designed specifically to meet the unique needs of local governments having the task of managing pavement assets. It sketches the environment in which such systems must work to set the terms of reference, discusses data collection requirements, covers pavement deterioration, comments on maintenance and rehabilitation treatment selection, and details the desirable budgeting capabilities.

Asset Management Strategy for Unsealed Low-Volume Roads in New Zealand

The majority of rural local roads in New Zealand are unsealed low-volume roads that require regular grading, and a contractor has developed an asset management strategy for unsealed roads. Key facets of this strategy included establishment of a companywide asset management team responsible for implementing the strategy, creation of a new senior management position dedicated to delivering this strategy, and integration of asset management principles and processes into normal business. This unsealed roads maintenance strategy identified the need for a low-cost, effective tool for roughness monitoring that quantitatively reflects the unsealed network condition and is not based on subjective perception, which is the current situation. After a review of all existing roughness measurement systems from around the world, the Opti-Grade system from Canada was acquired and is being used on unsealed road networks throughout New Zealand. An example of the benefits of outsourcing road maintenance to private contractors is the fact that it was the contractor that identified the need for a low-cost roughness measurement tool to provide an objective operational performance indicator for rural local roads, initiated the development described in this paper, and implemented its use. This paper explains the processes involved in developing and implementing this strategy and the benefits to both the road authority and the company.

Log Truck Transportation on Public Roads in New Zealand: Regional Network Analysis with Geographic Information Systems

Industrial forestry within the Southland region of New Zealand is forecast to double over the next 20 years as the availability of wood from production forest plantations increases dramatically. This is generating unprecedented pressure on the public road network. An issue has arisen between government and industry over which should pay for the increasing road upgrading, rehabilitation, and maintenance costs generated by the burgeoning traffic, with the Southland Regional Council proposing a fourfold increase in the road-related rates (tax) charged to the forest industry. In an effort to produce an independent model of the forest industrys use of the road system, regional spatial data sets characterizing the wood supply, demand for wood, and road network were assembled and verified. The transportation geographic information system software package TransCAD was then used to determine the optimum distribution pattern for Southlands wood production. It was confirmed that an accurate model of the current transportation of wood in the region had been created. Distribution patterns under four input scenarios were analyzed. For domestic sawlogs, rearranging supply contracts was predicted to provide transportation savings, measured in annual tonne-kilometers, of just under 40%. On the other hand, there appeared to be no gains to be made in using unconstrained haul routes—the routes in current use are near the optimum. The predictive power of the model was illustrated for the case of chip logs, in which significant changes in traffic patterns were predicted for the 2009 harvest year, along with an order-of-magnitude increase in traffic volumes. The work revealed that the origin of the fourfold rate increase to be charged to forestry is in an arbitrary “perceived damage factor” applied to the numerically modeled traffic flows.

REGIONAL NETWORK ANALYSIS OF PRIMARY-INDUSTRY TRUCK TRAFFIC ON PUBLIC ROADS IN NEW ZEALAND BY USING GEOGRAPHIC INFORMATION SYSTEMS

Industrial forestry activities in New Zealand are now in a phase of unprecedented growth: the annual cut will double from 18 million m3 to well over 30 million m3 a year during the next 5 years. Given that most of the wood is taken from forest to mill or port by road in New Zealand, including a portion of the trip on public highways, the impacts of the doubling in logging truck traffic will be significant and severe. New Zealand’s roads have, for the most part, thin-sealed, unbound pavements. New Zealand’s second-largest industrial sector is tourism. Pavements and tourists will feel the impact of the looming increase in logging truck traffic unless steps are taken to anticipate the changes in traffic volumes and patterns. There is the complicating factor that the dairy industry too is now expanding rapidly with associated increases in raw milk tanker traffic. There is some friction between the forest industry and the dairy industry over which will be responsible for the increased strengthening, rehabilitation, and maintenance of roads. Research is under way to use regional network analysis and geographic information systems to predict the increases in heavy-truck traffic and changes in its distribution on public roads. This is the first step toward devising measures to mitigate the impacts and is a precursor to the implementation of pavement management. A unique opportunity exists in southern New Zealand: cooperation between forest operators and government agencies in the Otago and Southland region of the South Island of New Zealand on large-scale projects, providing the environment needed to examine such large, landscape-scale problems.

High-Strength Geotextiles in Ultraheavy-Load Haul Roads

The heaviest trucks serving shovel-and-truck mining operations have tripled in weight to more than 600 tonnes gross weight over the past 30 years. The design of haul roads to support these trucks is becoming ever more challenging. An additional problem is the huge demand for aggregates with which to construct these thick, wide roads. In this study of the problem, a numerical modeling investigation was performed for a 300-tonne-design axle on a granular pavement consisting of a capping layer, base, and subbase (0.5, 1.0, and 1.5 m thick, respectively). Conventional linearly elastic analyses and analyses not permitting tension were carried out. While the results of the conventional elastic analysis permitting tension had indicated that there was no reinforcing effect with these geotextiles, the results of the no-tension analysis indicated a significant reinforcement effect attributable to the inclusion of high-strength geotextiles in the cross section. The results bring into question the use of analyses permitting tension in the granular pavement materials.