Observation

A good number of candidates were able to:
-           State two reasons for providing temporary support to sides of excavation
-           list four desirable properties of aggregates for the production of concrete.
However, many of them failed to sketch a cross-section through a retaining wall and indicate the following:

1.  heel;
2. toe;
3. weep hole;
4. retained earth.

The expected response to question 2 is as given below:

2(a)       Reasons for providing temporary support to sides of excavation:

1. safety of the men working in the trench;
2. safety of adjoining  properties when the excavation is to remain open for a long time;
3. when the excavation is deep;
4. where the soil is loose;
5. to warn passer byes of the existence of trench excavation works;
6. to prevent delay of work due to collapse of trench.

        
(b)       Desirable properties of aggregates:

1. should be clean;
2. should have a satisfactory strength;
3. must be durable;
4. must be well graded;
5. must be inert;
6. must be free from salt;
7. free from organic impurities;
8. non polishing/wear resistant.

(c)        Retaining wall: