Site investigation and design of a grade separated intersection in Harare, Zimbabwe

Abstract

The aim of the paper is to design a grade separated intersection at Seke Road and Cripps/Dieppe Road in Harare, Zimbabwe. During the peak hours on weekdays, congestion and long queues occur at Seke Road and Cripps/Dieppe Roads intersection in Harare, Zimbabwe therefore there is need to improve this intersection. Significant traffic and congestion across urban areas creates a demand for grade separated intersections. The construction of these structures plays a critical role in the development of modern infrastructure due to safety, environmental, and economic reasons. With the increase in traffic there is need for an improved intersection. The scope of the work included an assessment of some of the intersections in Harare where grade separation is feasible, selection of one intersection, design of the grade separated intersection according to appropriate design standards and production of a bill of quantities. The project includes a traffic counting survey which was conducted for the purpose of determining the traffic volumes and hence the justification of upgrading the existing intersection. The methodology included production of a map, traffic counts, collection of secondary data on traffic counts, conducting geotechnical investigation tests and geometric and structural design of the intersection. Geotechnical investigation results were also used to determine the foundation depth of the bridge. The project contains literature of the different types of intersections, the advantages and disadvantages and also the different types of bridges. The traffic data was analysed and the most appropriate intersection design was chosen. The Simple Diamond interchange was designed because it is cost effective as it reduces congestion at Seke Road and Cripps/Dieppe Roads intersection. However the intersection should be further upgraded to a full clover leaf or a three level intersection within the next 20 years so as to avoid congestion again due to high traffic volumes. The interchange is a Simple Diamond interchange which was designed according to South African Standards. The analysis was carried out using Prokon Software, AchiCAD software, Microsoft word, AutoCAD and Microsoft word. A physical model was also made for the design. It is recommended that pre-stressed beams can be cast on the open space available and lifted by cranes to their positions and the grade separated intersection should have more columns for aesthetic reasons.