3.1 What is the main function of a manhole?
3.1.2 Identify A - NSC Civil Technology Civil Services - Question 3 - 2018 - Paper 1
Question 3
3.1 What is the main function of a manhole?
3.1.2 Identify A.
3.1.3 Identify B.
3.1.4 Manholes that are deeper than 750 mm should be set in frames and have grease... show full transcript
Worked Solution & Example Answer:3.1 What is the main function of a manhole?
3.1.2 Identify A - NSC Civil Technology Civil Services - Question 3 - 2018 - Paper 1
Step 1
What is the main function of a manhole?
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Answer
A manhole is a chamber that allows entrance to a drain, enabling access to the sewage pipes of a sewage system.
Step 2
Identify A.
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Answer
A represents the 'Benching/Sloping/Haunching' structure inside the manhole, which facilitates draining and maintenance.
Step 3
Identify B.
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Answer
B indicates the 'Pipe channel/Open channel/Channel' which directs the flow of sewage within the manhole.
Step 4
Manholes that are deeper than 750 mm should be set in frames and have greased double seals. Give TWO reasons why greased double seals are installed.
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To make the manhole airtight, preventing the escape of gases. 2. To ensure that liquids cannot escape, maintaining the functionality and hygiene of the sewage system.
Step 5
State THREE regulations that protect workers during excavations.
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The supervisor must ensure that no load, material, or heavy machinery is placed near the edge of any excavation.
Excavations must be adequately protected by a fence.
Personal protective equipment must be worn by any person entering an excavation trench.
Step 6
What type of shoring, A or B, will be suitable to use in loose or water-logged soil?
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Type A shoring will be suitable in loose or water-logged soil as it provides better stabilization and support.
Step 7
Motivate your answer to QUESTION 3.4.1.
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A shoring system is designed to prevent soil from collapsing during excavation, which is essential in unstable, loose, or saturated soil conditions that are prone to shifting.
Step 8
3.5.1 Working in confined spaces, such as a (manhole/french drain/excavation), is one of the most dangerous tasks.
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A manhole is indeed one of the most dangerous tasks due to limited access and hazardous conditions.
Step 9
3.5.2 A safety harness is clipped to a rope known as a (safety rope/lifeline).
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A safety harness is clipped to a lifeline, enabling safe work in potentially dangerous environments.
Step 10
Calculate the volume of concrete that will be used for the foundation.
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Answer
To calculate the volume, use the formula: Volume = length x breadth x height.
Assuming the dimensions are as follows:
Length (l) = 1.150 m
Breadth (b) = 1.0 m
Height (h) = 0.125 m,
The volume of concrete required would be:
Volume=1.150imes1.0imes0.125=0.14375extm3
Rounded to TWO decimals, the volume = 0.14 m³.
Step 11
Calculate the number of bricks needed for the manhole.
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Given:
The wall is a one-brick wide wall.
The centerline for the brickwork of the manhole is 4.96 m.
Using the following:
100 bricks per square meter,
Then:
Area of the wall = 1 m width x 4.96 m height = 4.96 m².
Total bricks needed = 4.96 m² x 100 bricks/m² = 496 bricks.
