A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
10. How can manholes be adapted to the final height of the pavement?
(M2)
Theoretically speaking, the whole manhole structures can be constructed
as a whole instead of splitting into two stages of construction. With detailed
calculation of longitudinal fall and cross fall of road pavement, it is possible
to place and construct the manhole cover and frame in accurate levels and
falls so that the whole manhole can be constructed in a single stage.
However, in actual practice it may not always be possible to accurately
predict the inclination and levels of future manhole cover. As such, it is not
uncommon that the construction of manholes is split into two stages:
(i) 1 st Stage: The lower part of manholes is constructed up to the access
shaft (about the level of sub-base). Then a rigid cover is placed over the
access opening of the manholes and bituminous materials are placed
on its top to construct the pavement.
(ii) 2 nd Stage: The bituminous material around the rigid cover is
removed and several courses of brickwork are normally placed on the
access shaft to adjust the level of manhole cover and frame to fit with
the final height of the pavement. Finally, manhole cover and frame are
installed in position as shown in the sketch below.
Fig. Typical details of manhole cover and frame
11. Why are some manhole covers designed into two triangular
halves? (M2)
Manhole covers are generally made up of two pieces of triangular plates to
form a square cover [23]. One may wonder why two rectangular halves are
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