Stormwater manholes and access chambers are traditionally constructed using precast concrete components supplied by concrete pipe manufacturers. Many years of good performance has provided confidence in the adopted approach. As a result manhole components have been accepted as fit for purpose and most TA specifications are related to hydraulic and operational requirements rather than the structural design.
The recent development of new performance design standards in New Zealand, has increased serviceability life expectancy of main infrastructure components to 100 years. Recent NZTA and TA specifications require a review of existing product designs to ensure compliance for “strength” and “durability”.
This paper presents the results of intensive research work conducted by the authors to achieve this goal. The main design parameters investigated were loading, load factors for the design of lids to suit various infrastructure construction conditions, lateral load on manhole walls, foundation stability and buoyancy.
Durability design is defined in the terms of the existing New Zealand Standards which define exposure conditions for which manhole components are designed to achieve 100 years life.
The paper also lists service conditions which allow designers to specify standard manhole components for safe bearing capacity, traffic loads and depth of installation. The conditions cover existing design and construction practices allowing designers to select the correct product or carry out an alternative specific design.