A Closer Look at Prevailing Civil Engineering Practice - European ...

A Closer Look at Prevailing Civil Engineering Practice, What, Why and How
Vincent T. H. CHU
carried out some time latter after initial tightening.
6. What are the limitations of CCTV regarding the inspection of
sewers
CCTV is a well-established and prevalent method for pipe inspection.
However, there are several limitations of CCTV technology:
(i) It could only provide the view of pipe internal surface above
waterline.
(ii) It does not provide the view of soil conditions surrounding the pipe.
(iii) Most CCTV system is incapable of measuring pipe gradient.
(iv) It does not provide any structural data on the integrity of pipe wall.
7. What is the difference between ductile iron pipes and steel pipes in
resisting external loads
Ductile iron pipes normally possess thicker pipe walls and are generally
stiffer than steel pipes. As such, it replies less on side fill soils to support
external loads. Hence, it is not necessary to achieve highly-compacted
soils for ductile iron pipes for sustaining external loads.
For steel pipes, owing to less stiffness associated with thinner pipe walls, it
relies heavily on the stiffness of backfill soils in resisting external loads.
Hence, to enhance the external load-carrying capacity of steel pipes, the
most convenient methods are to improve the quality of backfill materials
and to increase the level of soil compaction.
8. What does the pipe thickness of ductile iron pipes generally larger
than that of steel pipes
Both steel pipes and ductile iron pipes use hoop stress equation to model
internal pressure design. The difference in pipe thickness arises as a result
of more conservative approach in DI pipes.
For ductile iron pipes, surge pressure is considered as part of design
pressure and they are added together before applying a safety factor of 2
as follows:
F( P + S)
D
t =
2Y
72