Design and maintenance criteria for unpaved roads

Unpaved roads, ie gravel-surfaced or earth roads, have been in use for millenia but recently problems have been encountered in transferring experience and technology to environments other than those in which they were obtained. In addition, a continual decrease in funding demands that the available funds be applied with the maximum effect, and this requires the use of pavement management system methodology. This paper develops an approach tor evaluating unpaved road performance and deterioration. Based on an extensive study in Brazil, equations for predicting the development of roughness, rut depth and gravel loss are developed. Furthermore, criteria for the passability of an unpaved road, as well as a minimum gravel thickness to protect the roadbed are presented. The Maintenance and Design System (MDS) combines these relationships together with user cost equations in a systematic manner which permits an evaluation of the interaction of the different factors. Most importantly, traffic was found to have the greatest influence on regravelling and blading strategies as well as on the total cost of unpaved roads. The MDS was also used to compare predicted and actual maintenance on the unpaved road network in the Bronkhorstspruit district and excellent agreement was found, signifying that on average the MDS is applicable to South African conditions. Ongeplaveide paaie, dws gruis- of grondpaaie, is reeds eeue lank in gebruik, maar in die onlangse verlede is probleme ondervind toe daar gepoog is om ondervinding en tegnologie toe te pas in 'n ander omgewing as waarin dit ontwikkel is. Boonop vereis die aanhoudende vermindering in beskikbare fondse dat hierdie fondse tot die beste voordeel benut word. Toepaslike metodes van plaveiselbestuur is dus noodsaaklik. In hierdie referaat word 'n benadering vir die evaluering van die gedrag en werkverrigting van ongeplaveide paaie bespreek. Gegewens verkry uit 'n breedvoerige studie wat in Brasilië uitgevoer is, word gebruik om voorspellingsmodelle te ontwikkel vir padongelykheid, wielspoordiepte en gruisverlies. Die vereistes vir begaanbaarheid van 'n ongeplaveide pad sowel as die minimum gruisdikte vir beskerming van die padbodem word ook aangegee. Die Onderhoud en Ontwerpstelsel (00S) kombineer hierdie verhoudings op 'n sistematiese manier met padverbruikeronkostes wat dan 'n evaluering van die wisselwerking van die verskillende faktore toelaat. Daar is gevind dat verkeer die grootste enkele faktor is wat die hergruis- e