PAVEMENT DESIGN MANUAL Volume I and Volume II

Introduction

This manual gives recommendations for the structural design of flexible pavement and
gravel roads in Ethiopia. The manual is intended for engineers responsible for the design of
new road pavements and is appropriate for roads which are required to carry up to 30 million
cumulative equivalent standard axles in one direction. This upper limit is suitable at present
for the most trafficked roads in Ethiopia.
The design of strengthening overlays for existing bitumen-surfaced roads is not covered in
this manual, as this is the object of the ERA
Similarly, the design of cement concrete surfaced roads is treated separately in the ERA

Road flexible pavements are intended to limit the stress created at the subgrade level by the
traffic traveling on the pavement surface, so that the subgrade is not subject to significant
deformations. In effect, the concentrated loads of the vehicle wheels are spread over a
sufficiently larger area at subgrade level. At the same time, the pavement materials
themselves should not deteriorate to such an extent as to affect the riding quality and
functionality of the pavement. These goals must be achieved throughout a specific design
period.

Pavements do deteriorate, however, due to time, climate and traffic. Therefore, the goal of
the pavement design is to limit, during the period considered, deteriorations which affect the
riding quality, such as, in the case of flexible pavements, cracking, rutting, potholes and
other such surface distresses to acceptable levels.

At the end of the design period, a strengthening overlay would normally be required, but
other remedial treatments, such as major rehabilitation or reconstruction, may be required.
The design method aims at producing a pavement which will reach a relatively low level of
deterioration at the end of the design period, assuming that routine and periodic maintenance
are performed during that period.

PAVEMENT DESIGN MANUAL Volume I and Volume II