The design and installation of culverts under high fill road embankments is a common challenge for roading projects in New Zealand’s undulating landscape. Soil loading from these high fills requires high load capacity pipes that may be outside the manufacturing capabilities of concrete pipe suppliers in New Zealand.
The design consortium for the Waikato Expressway, Huntly Section addressed this challenge using a collaborative approach involving the Constructor, Designer and Supplier. Our consideration of design, manufacturing process, construction and health and safety measures gave us a workable, safe and cost-effective solution using commonly manufactured concrete pipes.
Our design and construction methodology involved designing the deep culverts assuming a negative projection installation while using a layer of expanded polystyrene (EPS) and subsequently constructing the trench in the same manner as an induced trench installation. This design was adopted to increase the negative projection design factor of safety; accounting for any non-conformances during construction. The pipe structural design by the pipe supplier was also optimised to utilise the available manufacturing resources, to achieve the design pipe classes using the thinnest possible wall thickness and reduce pipe mass, and therefore craneage. The construction methodology thus formulated provided a safer and cost effective solution as it removed the need for trench shields and risks associated with working at heights.
The paper will conclude with a review of the lessons drawn from the approach, the actual construction of the culverts and recommendations for future research to better understand the pipe-soil structure interaction in an induced trench installation.