The paper describes an environmentally optimised approach to the design of low-volume roads (LVRs) in which the in situ strengths of the subgrade and pavement layers at the anticipated in-service moisture condition are used for design rather than soaked values. It describes how the assumptions and simplifications inherent in the more traditional California bearing ratio (CBR)-based methods of design tend to produce less-than-optimum solutions compared with the dynamic cone penetrometer (DCP) method. DCP measurements are much more reliable than CBR measurements and are also quick to perform; hence, a relatively large number of measurements of subgrade strengths (for new roads) and pavement layer strengths and thicknesses (for upgrading projects) can be obtained, thereby reducing risks of inadequate data for design purposes. Research has shown how material specifications for LVRs can be relaxed and the paper shows how this aspect is integrated into DCP design methods. The paper reviews the alternative methods of DCP design, summarises the advantages of these methods and recommends some improvements. Transport Volume 169 Issue TR3 Designing low-volume roads using the dynamic cone penetrometer Rolt and Pinard
Understanding how roads behave is necessary both for their design and also to make sure that suitable and appropriate maintenance is programmed and carried out effectively. The problem is that this is not an easy task because there are many variables that affect road performance, and these differ from place to place. This is true of both paved and unpaved roads. Most countries have a large network of rural unpaved roads that require regular maintenance at relatively high total cost over many years. If the performance of such roads can be improved, especially in whole life terms, their costs can be reduced. Decision support tools such as the highway development and management system have been developed based on several studies in different countries. The performance models developed as a result of these studies often contain many variables and require extensive data collection before they can be used. This is often beyond the resources available. To improve this situation and to develop better understanding of the performance of gravel roads, this study was undertaken in six countries. It was found that two material characteristics, namely plasticity product and grading modulus, had a major effect on the performance of gravel roads, and were found to predict the performance of gravel roads to an acceptable level of accuracy. The results of the study were used to develop a simple life-cycle costing model for gravel roads that allows engineers to improve the performance of gravel roads and to reduce whole life costs.
Under the Research for Community Access Partnership (ReCAP) funded by the United Kingdom Aid (UKaid) program, a project entitled ‘Development of Specifications for Low Volume Sealed Roads through Back Analysis’ was carried out. Previous studies on the performance of low volume sealed roads have emphasized the importance of good drainage to ensure good performance. The emphasis has been on providing sealed shoulders, adequate crown height, and adequate camber. These studies have not related these cross-sectional features with materials characteristics. This paper investigates the influence of each of these features on the performance of low volume sealed roads and their relation to pavement materials. The features were considered each one at time, using a matrix of three levels of the value of each feature and three levels of performance categories. Thus, presenting a 3 × 3 performance matrix for each factor. Assessment of the matrices showed that provision of sealed shoulders permits the use of materials of higher plasticity (PI ≤ 16 and PM ≤ 560) without compromising performance compared to that permissible for sections with unsealed shoulders (PI ≤ 10 and PM ≤ 240). These results can be used to supplement existing selection criteria for road base material of low volume roads.
Correct interpretation of the cause or causes of defects and deterioration of road pavements is important for the selection of the most appropriate maintenance or repair strategies and for the design of new pavements. However, identifying the cause of pavement defects is not as simple as merely looking for aspects of specifications that have not been fully met. The cause of failures is often attributed to a number of factors, one of which, if absent, would not necessarily result in any defects. This paper describes and analyses three case studies where three different mechanisms have caused the deterioration of both asphalt concrete and double chip sealed surfacings. The first mechanism is the peculiar formation of potholes below certain structures and trees, which can result in large-scale ravelling and potholing on certain road categories. The second mechanism is an unusual cause of the flushing of bitumen on both types of surfacing. The third mechanism results in the formation of potholes at roundabouts in tropical countries. The paper concludes by recommending the appropriate maintenance measures for the cause of each defect and appropriate designs to minimise the likelihood of their occurrence.
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