building construction Paper 2 WASSCE (SC), 2017

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:

  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: