Regional Seminar Proceedings 1990

3. DISCUSSION ON ALIGNMENT CONTROL

3.1 DEFINITIONS

For the purpose of the discussion the method outlined in this paper and other similar methods will be termed as the profile method, also the mehtod using slots to create a level platform from which to excavate the drains and create the camber, will be termed as the slot method.

3.2 PROFILE METHOD

The method proposed in this paper was wholeheartedly supported by the participating experts from Botswana and Zambia (who were using this method). In Zambia the project had slightly modified the approach but found it to be successful in a variety of terrain including steep terrain. Other participants found level control for drainage also very important in rolling or flat terrain.

Using this method engineering advice on site should only be necessary in difficult areas after the foremen have been trained to carry out the design/setting out functions.

Casual labourers are good at ensuring the correct shape of road cross-section during construction but the lingitudinal control is not there unless there is 100 to 200 metres set out and properly adjusted for level at one time in advance of the work. In comparison the levelling of slots tends not to be carried out over long sections of road therefore making it difficult to produce a good vertical alignment.

Fears were also expressed that the large number of profiles needed for setting out in the profile mehtod would interfere with the increased traffic levels expected in Minor roads in Kenya and Regional roads in Tanzania. Those using the profile method said that the profiles once aligned could be replaced by pegs and string lines thus reducing any interference with the traffic.

3.3 METHODS USED BY DIFFERENT PROJECTS

Mbeya has employed a method which uses slots plus mobile profile for vertical alignment. Tanga is using the slotting method as is Mozambique. Rukea has used the slotting method but has proposed to try the profile method on the next road to be rehabilitated. Kenya are continuing with the slotting method which they find is perfectly adequate on green field sites. However in the coming year they will be assessing alternatives as some problems have arisen when upgrading badly eroded roads or roads in restricted areas such as those adjacent to fields with high value crops. They will be producing a technical manuals from their findings.

3.4 SLOTS METHOD

The slot method has proven very successful for the rural Access Roads Programme in Kenay, but there are reservations about its suitability for the Minor Roads Programme. It was argued that some of the difficulties in producing a good finish to the road were problems with management rather than at site level and therefore a change in method would not solve these problems.

One of the advantages of the slot method is the ease with which the foremen can calculate the task rates for the casual laboureres once they have created their level platform. Using the profile method the volume of work will be constantly varying. In Zambia, the project has issued tables to the foremen so they can read off the quantities and task rates for a given depth of excavation thus easing this problem.

3.5 LIGHT GRADING OF THE ROAD SURFACE PRIOR TO GRAVELLING

When dealing with the question of the quality of the road surface finish, there was a suggestion that light grading could smooth the surface of an earth road befor ethe placing of gravel. The argument for carrying out this work was a better finish to the road and a saving in the quantity of gravel used. The arguments against were that if people know a grader is coming they will take less tourble to ensure a good standard of finish by hand. The grader is an additional cost and may not be sustainable and will not remove large ruts.

3.6 GUIDELINES

It was proposed that John Marshall and Walter Illi look at the different methods used in various projects and perpare general guidelines on the methods for producing an acceptable road alignment with functioning drainage. They were asked also to co-operate with Gary Taylor who will be carrying out a similar study in Kenya. The suggestion was made that those projects using the profile method should not be too rigid in their recommendations as the method was developing all the time.

3.7 TRAINING

Trainers should have clear guidelines stating what the engineers need from trained foremen and supervisors. There is a need for an urgent decision on method and training, in Tanzania, before the Ministry of Communication and Works start their large training programme.

3.8 AGREED PLANS FOR ACTION, CONTROL OF ALIGNMENT