The effect of environmental factors and traffic volume on the performance of low-volume labour-based roads

Abstract

In road works labour-based technology refers to the appropriate and efficient use of labour in construction and maintenance, with equipment only playing a supportive role. The technical specifications related to the technology were developed and modified to suit efficiency and safety requirements in the utilisation of labour. However, lack of road deterioration relationships to determine performance and improve the specifications and designs is still a problem. The objective of this research was to study influence of the environment and traffic factors on the performance of unpaved low-volume labour-based roads in Uganda. The research methodology included review of the existing literature, road condition surveys and material sampling and testing, performance-monitoring on labour-based roads for 2.5 years and development of road deterioration models. This research established that roughness index is a function of traffic volume, dust ratio of wearing course, rainfall and road geometry. The rate of gravel loss is a function of traffic volume, rainfall and plasticity product, dust ratio and grading modulus of wearing course. The IRI roughness index is 6.1 m/km and rate of gravel loss is 15.3 mm per year for the low-volume roads. It was further established that the annual gravel loss due to environment effects is 15.2 mm for low plasticity gravels and 11.5 mm for high plasticity gravels. Further analysis established that road deterioration can be estimated by the HDM-4 Model using calibration factors of 0.44 for roughness and 0.97 for gravel loss. In conclusion the research achieved its objective by developing road deterioration relationships which can be used to improve designs, specifications and determination of maintenance standards for low-volume labour-based roads. However, it is recommended that further research could be undertaken to model the effect of more climatic factors (precipitation, evapo-transpiration and storage capacity of the soils) not covered under this research.