Culvert Installation

Document No:  67-08-79
Revision:  2A
Date amended:  29-Mar-2019

Image: orange line.RCN-D13^23151823.GIF The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Eric Cheung by e-mail or on (08) 9323 4402.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

Revision Register


Ed/Version Number Clause Number Description of Revision Date
1 All Guideline Developed and Approved. 29-May-2003
2 Header Contact person changed. 23-Jan-2014
​2A​Header​Contact person changed.​29-Mar-2019

Table of Content


All culvert installations should be carried out in accordance with Main Roads Standard Culvert Drawings and Main Roads Specifications 404 Culvert and Stormwater Drains and relevant Australian Standards.


3.1 Space Between Barrels In Multiple Culverts

3.1.1 Pipe culverts

Pipes laid in two or more lines in the same trench or streambed should be separated enough to allow space for thorough compaction of backfill, whilst ensuring side support of the culverts to prevent collapse of the pipes due to unequal loading.

3.1.2 Box Culverts

As shown on the Main Roads standard box culvert drawings, no separation is required between barrels of multi barrel box culverts.


3.2 Installation Conditions

The two common types of installation conditions are embankment type and trench type and are described below.

For each installation condition, there are five degrees of pipe support possible, as described in AS 3725-1989.  The design loads on pipes depend on whether the fill material is cohesive or non-cohesive, and on its density. Where the actual material densities vary from the assumed values, the design load should be calculated from AS3725-1989.

3.2.1 Embankment Condition

The embankment condition applies to a culvert barrel laid on the stripped surface at the base of a fill. If the Designer does not have detailed information about the foundations, or the culvert barrel is laid partly in trench and partly in fill, or the foundations are poor so that any trenches must be excavated wider than the minimum required for the trench condition, the embankment condition may be assumed for design. Where the design is not based on the embankment conditions, the type of installation assumed must be clearly stated on the construction drawings.

3.2.2 Trench Condition

The trench condition applies where the excavation starts from the natural or finished surface, and no fill or other loading affect the trench.

Since the load on the culvert barrel and the cost of excavation both increase with increasing trench width, the trench should be as narrow as possible. About 0.3m clearance is necessary if effective sidefill compaction is needed, and about 0.6m is needed to use a mechanical compactor.  When cement stabilised backfill is used (refer Main Roads Specification 404 Culvert and Stormwater Drains), side clearance may be reduced to 0.15m.


3.3 Pipe Bedding and Culvert Backfill

As shown in Main Roads Standard Culvert drawings, all culverts which use the trench method for installation should be backfilled with cement stabilised backfill.


Main Roads Specifications 404, Culverts & Piped Drains

AS 3725, Loads on Buried Concrete Pipes; (1989).