Question 2
(a) State two reasons for providing temporary support to sides of excavation.
(b) list four desirable properties of aggregates for the production of concrete.
(c) sketch a cross-section through a retaining wall and indicate the following
(i)heel;
(ii)toe;
(iii)weep hole;
(iv)retained earth.
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:
- heel;
- toe;
- weep hole;
- retained earth.
The expected response to question 2 is as given below:
2(a) Reasons for providing temporary support to sides of excavation:
- safety of the men working in the trench;
- safety of adjoining properties when the excavation is to remain open for a long time;
- when the excavation is deep;
- where the soil is loose;
- to warn passer byes of the existence of trench excavation works;
- to prevent delay of work due to collapse of trench.
(b) Desirable properties of aggregates:
- should be clean;
- should have a satisfactory strength;
- must be durable;
- must be well graded;
- must be inert;
- must be free from salt;
- free from organic impurities;
- non polishing/wear resistant.
(c) Retaining wall: