Alex T. Visser

Development of Real-Time Mine Road Maintenance Management System Using Haul Truck and Road Vibration Signature Analysis

The unpaved road network of a surface mine is extensive, comprising numerous roads of varying construction and material qualities with highly variable traffic volumes. Existing haul road maintenance management systems (MMSs) work well for predictable traffic volumes, but for complex mine road networks, the MMS becomes onerous and results in suboptimal road maintenance strategies, with the attendant increase in total road-user costs and reduction in service. A real-time MMS was thus sought to overcome the deficiencies of existing systems for mine roads. Because most large mines operate trucks with onboard diagnostic data collation, linked through a centralized communication and Global Positioning System backbone, it was proposed that road condition could be monitored on a real-time basis through onboard vibration signature analysis. A real-time mine haul road MMS was developed. Mine road maintenance practices were reviewed. The real-time system architecture was devised, and a field trial was conducted of onboard vibration signature assessment. Trial results were evaluated in the light of road defect signature recognition, analysis, signature repeatability, and system limitations. This approach is applicable to other situations, such as a network of district roads, subject to an analysis of economic feasibility. The conclusion is reached that modern technology has the potential to apply maintenance as and where needed, with possible reductions in authority cost and an improvement in service provided to road users.

MANAGEMENT OF UNPAVED ROAD NETWORKS ON OPENCAST MINES

In surface mining operations, ultra-heavy-haul trucks apply axle loads in excess of 200 t, but the daily load repetitions are low. Road networks for these vehicles have historically been designed empirically, relying heavily on local experience. Increasing vehicle sizes have resulted in unwarranted deformations and excessive maintenance requirements. There was thus a need to consider the transportation problem holistically, taking into account construction and maintenance costs as well as vehicle operating costs. Most opencast mines in South Africa are private endeavors, and all savings will benefit the company. A research project was undertaken in South Africa to develop a management system that takes into account different design factors. The various components of the management system are presented, and the value of its application is demonstrated through case studies. The structural design system, the pavement deterioration system, and the maintenance effectiveness are discussed. The components are then combined to provide total transportation costs and the appropriate maintenance regime to minimize total transportation cost. The system has been applied on several mines, and distinct benefits have been derived. The improved structural design of a new road resulted in a 29 percent savings in construction costs, compared with the tendered price of the empirically designed structure. In addition, improved wet weather trafficabililty was noted. Mines have also used the system as a motivation for improved maintenance equipment and strategies because significant benefits were apparent from the adoption of the maintenance management system.

Condition-Triggered Maintenance for Mine Haul Roads with Reconstructed-Vehicle Response to Haul Road Defects

The management of unpaved mine road networks—characterized by high axle loadings, low traffic volumes, variable materials and construction quality, and rapid rates of deterioration—is often inadequate. This situation results in either overmaintenance of the road or failure to recognize significant deterioration, which both lead to the application of suboptimal road maintenance strategies with the attendant increase in total road-user costs. A real-time condition-triggered maintenance management system was identified as a solution, in which onboard monitoring of vehicle dynamic response to road condition forms the basis of road defect recognition and maintenance response. A practical approach to road defect reconstruction using measured truck response is presented. Initially, the application context is introduced, then the field testing program is described, in which data sets were generated that served as the basis for mathematical modeling of the truck response. A modeling approach utilizing the concept of independent front suspension dynamic equilibrium is described as the basis for road defect recognition. On the basis of measured suspension forces and the acceleration of the unsprung mass, the approach to tire force and road defect reconstruction is presented. It is concluded that the methodology developed enables reconstruction of road defect geometries with an accuracy sufficient to allow specific types and dimensions of defects to be recognized for the purpose of road maintenance. By extending the methodology to public unpaved roads, maintenance could be applied as and where needed with a resultant reduction in authority cost and improvement in service provided for the road user.

Flexible Portland Cement Concrete Pavement for Low-Volume Roads

One of the challenges of South African civil engineers is to develop techniques for infrastructure provision appropriate to local conditions and suitable for creating employment. Local technology, consisting of welded plastic cells known as Hyson-Cells, is identified as a potential solution. After tensioning the cells, coarse aggregate is placed and compacted, after which a sand-cement grout is vibrated into the voids in the coarse aggregate. Alternatively, ready-mixed concrete can be used. The design catalogue for geocell pavements for low-volume roads is presented, and the suitability of the catalogue is demonstrated by evaluating streets that had been in service for more than 5 years. The catalogue of pavement structures was developed from the results of a laboratory study and field trials. An evaluation of eight road projects that had been in service for more than 5 years supported the structural design but also showed that construction control was important to ensure good performance. An economic analysis demonstrated that it was competitive with other pavement types normally used on access streets.

Procedure for Evaluating Stabilization of Road Materials with Nontraditional Stabilizers

In response to the need to find cost-effective stabilizers, a large number of chemical products are being marketed as potential solutions. Traditional laboratory tests have not been able to predict the performance of these materials satisfactorily. A solution is for suppliers to construct experimental sections several hundred meters long. However, that becomes an expensive exercise, since each type of soil in a region would have to be used. An evaluation technique has been developed that allows test panels to be constructed in the field at low cost with a range of soils and stabilizers and that takes into account local environmental conditions and traffic. The aim of this paper is to present this evaluation technique and the results with a range of stabilizers and soils. The paper describes construction of the 1- × 3-m test panels and the subsequent testing protocol. Several materials, ranging from sandy to clayey, were tested with different generic stabilizers, such as polymers, enzymes, and ionic soil stabilizers. Control panels without additives were also constructed. The testing regime conducted over 8 months included regularly measuring the following: the in situ California bearing ratio with a dynamic cone penetrometer, both at the in situ moisture content and after soaking for 2 h; density and moisture; and permeability. Visual observations about performance were also noted. The test panel procedure is a cost-effective solution for evaluating the potential strength gain of stabilizers with a range of soils. As is known, stabilizers must be tailored to soil properties, because stabilizers do not all have the same effect.

INNOVATIVE AND COST-EFFECTIVE SOLUTIONS FOR ROADS IN RURAL AREAS AND DIFFICULT TERRAIN

In many parts of the world, high-level engineering solutions are inappropriate for rural areas where expertise, skills, and equipment are unavailable. Often these areas suffer from difficult terrain that also makes accessibility a problem. At the 1999 International Conference on Low-Volume Roads, a design catalogue was presented for a flexible portland cement concrete pavement using geocells, which was suitable for labor-intensive construction. However, the catalogue required layer works, which meant that construction equipment, although minimal, was required. This was seen as a major constraint, particularly when communities become involved in the construction of these local access roads. In addition, in difficult terrain the handling of drainage becomes a major engineering undertaking for which expertise may not be locally available. The aim of this study was to develop a structural design catalogue that caters for the range of traffic and material conditions typically encountered in these remote rural areas. Additionally, standard solutions were developed for dealing with steep gradients and surface drainage that are coupled to the structural design. The fundamental engineering principles were used to derive the structural design catalogue and in the management of surface drainage. Case studies were conducted in the successful application of the design catalogue to demonstrate the approach and design procedures. This approach has made a significant contribution in improving the quality of life of rural communities, particularly in remote and often poor regions of South Africa.

Comparison of bitumen–rubber use in extreme conditions in Russia and South Africa

The development of the use of crumb rubber from used tyres in asphalt started in the USSR during the 1960s independently and in parallel with the research in the USA and Western world during the 1970s. The result is that different processes were developed for making bitumen–rubber (BR) asphalt. The objective of the paper is to present and compare the BR specifications and asphalt experience in Russia and in South Africa (which was derived from the USA approach). The focus is on the wet process even though more recently the dry method has been used. First, the properties of the constituent components are presented and discussed, thereafter the properties and manufacture of BR are compared. Finally, the properties of BR asphalt are compared and the experience and performance is presented. It was found that although the initial approach from the two schools differed, there are currently major similarities, even though the temperature ranges of use are vastly different. BR has been shown to cater effectively for a wide range of environmental conditions and is superior to unmodified bitumen.

Design Guidelines for Low-Volume Macadam Pavements in South Africa

Macadam principles in pavement engineering were applied in South Africa up to around 1960. Mechanization and increased production requirements led to a decline in the use of macadam layers. More recently interest in macadam pavements in South Africa was renewed because of the labor-friendly construction methods. Much of the experience that had been available was lost as people retired, and new techniques of construction gave a new perspective. There is thus a need to provide guidance to new entrants to the industry and capture the experience that was common knowledge several decades ago. The aim of this report is to present a guideline document for construction of appropriate and economic macadam pavements based on extensive South African research coupled with vast experience in the construction of these layers. Guidance on appropriate use of the different variants of macadam layers, the material properties, the structural design process and catalogue, functional design considerations, and construction practice is provided. It was found that under the current socioeconomic upliftment program macadam principles provide an appropriate and cost-effective solution to paving urban streets.

Evaluation of Sustainability of Low-Volume Roads Treated with Nontraditional Stabilizers

The use of nontraditional stabilizers to treat unpaved (mostly low-volume) roads has received attention over the past several years as various types of stabilizers have been developed and become available. Evaluation of the sustainability of various infrastructure actions, including the provision and maintenance of roads, is becoming more relevant as the effects of actions taken in the natural environment on itself and on the human environment are evaluated and understood in more detail. The Greenroads rating system offers a method for evaluation of the sustainability of the design, construction, and maintenance of roads. The system was developed with a focus on surfaced higher-volume roads. In this paper, the potential applicability of the Greenroads system for the evaluation of the sustainability of unsurfaced low-volume roads is investigated through two case studies of experiments in which unpaved low-volume test sections were treated with various types of traditional and nontraditional material stabilizers. Appropriate parameters were selected from the general Greenroads metric to ensure that those affecting unpaved low-volume roads would be evaluated (e.g., runoff quality and use of regional materials) while parameters such as paving emission reduction were excluded from the analysis. The assumption was made that all compulsory project requirements would be met by each of the options evaluated. It was concluded that the Greenroads metric can be used to evaluate the potential sustainability of unpaved low-volume roads treated with nontraditional stabilizers and that the metric can provide insight into the potential effect of various parameters on the sustainability of the various stabilization options.

INVESTIGATION OF THE FOAMABILITY OF TAR AND THE CHARACTERISATION AND OPTIMISATION OF FOAMED TAR

ABSTRACT In southern Africa the scarcity of good road construction materials and long haulage distances have necessitated the use of methods to improve substandard materials or re-use by means of recycling. Tar is available in large quantities as a by-product of the fuel-from-coal process. The good adhesive properties of tar to aggregate are well known, but suitable construction processes limited the use of tar. Foamed bitumen (asphalt in the US) has been used extensively, and because of the low temperature application has major construction benefits. Due to the similarities in properties between bitumen and tar it was anticipated that tar could be used as a stabilising agent in the same manner as bitumen. The aim of the paper is to investigate the potential of foaming tar, and to present the key design parameters. The paper first presents the properties of tar, and specifically addresses the health considerations of low temperature carbo-tar which was the focus of this study. Thereafter the characterisation of foamed tar based upon the principles developed for foamed bitumen is presented. Foamed tar is investigated with respect to expansion ratio and half-life, and a new parameter known as the Foam Index. Optimisation methods for the foamability of tar are formulated with respect to the Foam Index, foaming temperature and foamant water content. Conclusions are drawn with regards to the tar foaming process and tentative limits are set with respect to the expansion ratio, half life and Foam Index necessary to achieve a satisfactory foamed tar stabilised material.