Drainage construction

These RMS videos provide information on drainage design and construction. They are divided into 7 training modules

RMS Construction Stormwater Drainage – Training Module R11 – Module 1
This module has information on:

Monitoring the manufacturer’s components

  • Its important the pipes are inspected as pipes can be manufactured with defects or have defects occur during transportation to site.
  • It is important that the products do comply with the appropriate Australian Standards and specifications.
  • Any site changes need to be certified by an Engineer.

Managing the environmental impacts

  • Work out where the natural water courses is currently going. If the surrounding land form will remain as it is. This is likely to be where the drainage system will go
  • Where the drainage system is designed to be installed in the existing water course location, there will need to be a temporary diversion of the creek so that proposed drainage system can be built. Consider lining the channel with a material like geotextile lined channel.
  • Consider acid sulphate soils

Considering the foundations of the drainage system

  • Inspecting the setout of the drainage line
  • Consider settlement particularly where drainage embankments are constructed over soft soils.
  • Design assumptions need to be shown on the design drawings.
  • Consider the support for drainage structures. There is an RTA technical direction CQTD 2009/08 that sets out a range of suitable treatments to support drainage structures.
  • Identify the removal of any inadequate material once the drainage system trenching occurs. It is important to consider where the replacement material that is necessary to replace inadequate material will be sourced from, from site or off-site.
  • Laying the pipes from the downstream side to the upstream side is a recommended practice
  • Put the right class of pipe in the right situation.
  • Bedding and backfill are done in layers consistent with the specification.
  • Headwall and cutoff walls are used to funnel the water into the pipe and prevent (piping) water flowing down the foundation or backfill material layer. This would lead to erosion of material.
  • Minimise the projects exposure to adverse weather conditions.

Considering the temporary construction loading as well as the permanent loading on the drainage system

  • Providing enough material above drainage structures during construction so that construction equipment can travel across the drainage system is an important consideration.

Designing the culver to meet the life of the road

  • AS3725 mentions two types of culvert installations: trench installations and embankment installation.
  • It can be the case that the culvert design may be above or below the natural surface of the inlets and outlets and the design of the culverts may need to be redesigned. This may affect the hydraulic efficiency of the drainage network. It might otherwise be that the natural surface for either the inlet or the outlet points may require adjustments and this is likely to have environmental consequences.
  • There is the possibility that there can be adverse grade beyond the road boundary. This can be due to a lack of survey or a lack of design.
  • Consider the clashes that might occur between underground utility services and stormwater drainage. Consider identifying any planned utilities and potholing any existing utilities to get certainty around any clashes between utilities and the drainage network.
  • Extending existing culverts with a new line there is a need to remove the existing wing wall and then excavate back down the existing drainage line by at least 500mm and neatly cut square, to allow for a connection between the old line and the new line to have sufficient length to make an appropriate connection.
  • If an extended pipe makes a bend at a joint then you will need a junction pit at the join. This pit should extend to the existing / ultimate level as there is a preference to not have buried pipes.

 

Drainage design software

Drains drainage design software