Author(s)

RICHARD ROBERT MWAIPUNGU, SABRY AHMED

Abstract

When problem soils form part of pavement or bed layers, they may negatively influence the performance of the pavement, if not appropriately addressed during the design stage. This can be readily noted in the way they impede free vehicles’ movement. This effect is due to the pavement’s conspicuous changes in load-bearing capacity with climatic changes, leading to pavement distress as a result of their structural deformation. The variations of these soils’ load-bearing capacity, which lead to pavement distress, are mainly related to these soils’ changes in moisture content during the dry and wet seasons. It is an established fact that the structure and behaviour of problematic soils varies with the origin and type of soil mineralogy, location, stress history and climate. These factors have immense influence on the design, construction and management of the sealed and unsealed roads’ pavements. In an effort to address problem soils’ challenges, Tanzania’s Ministry of Works Pavement and Materials Design Manual (TMoW-P&MDM), which came into being in 1999, has attempted to describe the measures that need to be taken to improve problem soils’ performance, when encountered as part of pavement layers or the roadbed. These measures vary in complexity depending on the type of problematic soil in question. This paper looks at the identification and classification of challenging clay soils, as given by TMoW-P&MDM, as a tool for appropriate remedial measures to be put in place, and makes global comparisons. Furthermore, this paper stresses the need for legal framework to compel conducting the preliminary site investigation. The authors’ opinion is that further improvement of local prediction models of problematic soils’ negative effects will come with an understanding of the key roles played by soil characteristics in influencing negative behaviour. Performance studies of soils under the interaction of traffic’s wheel loads and climatic changes will further add to said improvement.

Keywords

clay, manual, pavement performance, roadbed, road design, soils, traffic, weather, wheel loads