The objective of the thesis for the doctorate by Mr. Klaus Dierks, Dipl.-Ing., is to develop optimised and appropriate technology for Namibian low-volume roads. In the thesis, special consideration has been given to economic, social and environmental parameters. The point of departure was an inventory of the Namibian roads system with all its structural and traffic data. Additional influences on Namibian road construction methods such as environmental and climatic factors were investigated. On the basis of these input data, appropriate road construction technologies based on existing and natural road building materials and traffic loads were analysed. These systematic investigations lead to cost and quality optimised systems, and these systems in turn were established on the basis of Namibian vehicle operating costs analyses. The results were compared with those of other vehicle operating costs investigations, such as the HDM-3 World Bank model. In carrying out these analyses and comparisons, the relationships between vehicle operating costs, riding quality and various pavement types (earth, gravel and paved roads with light surface dressings) were determined.

The next step in the optimisation process was a comprehensive performance analysis with quality ratings for a wide spectrum of pavement types. Deterioration mechanisms caused by roughness, cracks, aggregate losses and bleeding in the case of paved roads as well as by ruts, gravel loss, corrugation, dust, loose material, stoniness, pot-holes, skid resistance and surface drainage in the case of unpaved roads were investigated. The identification of these deterioration mechanisms resulted in revised material specifications for different pavement technologies. Furthermore, they resulted in optimised maintenance models for Namibian conditions. A further result of the investigations was the establishment of limits of statistical acceptance and rejection criteria by questioning road users. These criteria showed the distress modes leading to unacceptable riding qualities which enabled the creation of cost and quality optimised pavement types.

Taking all the given parameters into consideration, and on the basis of the economic analyses, the optimal points of grading, gravelling and paving of earth and gravel roads were determined.

The suggested appropriate construction standards for different road types were compared with the standard for roads in the Third World as proposed by the German Ministry of Economic Co-operation.

The research carried out for this thesis lead to significant new knowledge, which has resulted in new concepts for road maintenance in developing countries. In realising the findings considerable savings can be expected.

Berlin, 13.February 1992

The Promoter: Prof. Dr. S. Huschek

Complete Doctoral Thesis