Practical culvert design observations in Queensland

Buried underground drainage structures are used to satisfy the hydraulic requirements of a given site/environment and are typically manufactured of reinforced concrete. With the improvement of culvert inspection technology incorporating robotic camera inspection post installation, discovery of cracked culverts has been an increasing issue. Reinforced concrete pipe culverts are known to crack for various reasons including transport, handling, placement, backfill, foundation quality and vehicle over-loading during construction. A culvert’s vulnerability to be adversely affected by these conditions can be a function of its design, particularly associated with installation conditions and strength class. This review focuses on these aspects from a geotechnical and structural perspective, for reinforced concrete culverts of rubber ring joint or flush joint type, with outside dimension greater than 375mm. The review highlights how the current culvert design process occurs and provides geotechnical and structural insight around the importance for designers to have a good working understanding of AS 5100.2:2017 and AS/NZS 3725:2007. Reference is also made to Queensland Road authority ‘Transport and Main Roads’ (TMR) Technical Specifications where modification to the Australian Standards has been made. The review also assesses, using finite element analyses, the accuracy of published methods used to determine vertical load from vehicle loading and soil overburden, and demonstrates how these findings may be relevant to the broader Australian and New Zealand region. Practical insights and suggestions on how analysis, selection of appropriate culvert class and detailed design information can be improved are also discussed.