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QUESTION 3
(a) List SIX positions where access must be provided in a drainage system.
1
2
3
4
5
6
(3 marks)
(b) State the minimum clearance that must be provided around a drain that is required to go through a
concrete foundation.
(1 mark)
(c) Give TWO reasons why lateral support of a drain is important.
1
2
(2 marks)
(d) Give FIVE situations where a drain may need extra protection against damage.
1
2
3
4
5
(5 marks)
(e) State FOUR functions of gully traps.
1
2
3
4
(2 marks)
(f) State THREE requirements that a gully dish and grate should meet when installed in accordance
with NZBC G13-AS2
1
2
3
(3 marks)
(g) When a sewer is likely to surcharge, what TWO precautions should be taken to avoid having the
drain overflow into a property?
1
2
(2 marks)
Total 18 marks
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Question 3.
a) 1. @ Change of sewer gradient
2. @ Change of sewer direction
3. Junction of two or more sewers (unless the branch drain is less then 2 meters and does not receive the discharge of a WC)
4. Where a sewer changes size
5. on straight lines intermediate under a 100m access chambers or alternatively rodding points may be used @ 50m (max.) intervals
6. as close as possible to the sewer connection or sewage tank
7. Just inside boundary if sewer is outside boundary
b) An opening is formed to provide a 50 mm all-round clearance and the opening masked with rigid sheet material.
c) 1. To prevent pipe from floating.
2. Protect from physical damage during construction.
d) 1. Where the drain has less than 500mm of cover or is deeper than 2.5 meters.
2. Where there is danger of tree roots penetrating the joints.
3. Where vehicular traffic is likely to pass over the drain.
4. Where drain is laid in wet or unstable ground.
5. Where the drain passes under a building.
e) 1. Provides an overflow point outside the building in the event of a blockage.
2. Incase of blockage, provides access to the drain/sewer system.
3. To stop sewer gas exiting the drain.
4. To receive the discharge of waste pipes
f) 1. Be 25mm above paved area
2. Be 100mm above unpaved area.
3. A grating that will allow surcharge
g) 1. Where sewers are likely to surcharge, an approved non-return valve and a holding chamber that can hold the discharge from the drain until the sewer flow is normal again should be installed (reflux valve).
2. A Tidal gully trap can be fitted to prevent backflow from any source.