'As constructed' information for underground pipelines can be difficult to obtain due to the nature of works involved (constant back filling).
Whilst every endeavour should be made to obtain the 'as constructed' information, these endeavours shouldn't place any person at risk nor infringe on occupational health and safety requirements.
Location of pipe centrelines at manholes/structures
Manholes and structures must be located in relation to title boundaries by offsets and ties, as well as MGA94(z55) co-ordinates. The manhole or structure location is based on providing both the location of the structure and pipe centrelines.
Offset distances to title boundaries are the primary measurements used to relate the pipe alignments to title boundaries. The inlet and outlet pipe centrelines at structures generally have the same offset distance to title and as such only one offset is noted.
Where the offset of the inlet and outlet pipes differ by 0.2m or more, then both offsets shall be annotated on the design plan. MGA94(z55) co-ordinates will be provided for both pipe centrelines, rather than to the centre of the manhole or structure.
The tie distance should generally be less than 5m with the 'as constructed' chainage providing the necessary relationship to title for greater tie distances.
MGA94(z55) co-ordinates of both asset and title provide a means of verifying the positional accuracy of the asset in relation to VicMap Property.