Safety and Sustainability in Design of Embedded Retaining Walls

Embedded retaining walls are commonly used in deep excavations for sections of retained cuts or cut and cover tunnels, in Transport Infrastructure projects. Safe, sustainable, and reliable design of retaining walls is critical, and sustainable designs can be evolved by optimisation of design approaches as well as by using alternate options and observational methods. This paper presents the challenges in the design of embedded retaining walls, following various design approaches and partial factors in accordance with the Australian Standards AS 5100, AS 1170, AS 4678, and Eurocode 7, using a live example from a station box excavation in a Transport Infrastructure project in Sydney. Results of finite element modelling using two constitutive models, demonstrate that the various design approaches and application of load and material factors based on the provisions in various Australian Standards, result in different design outcomes. The effects of action in terms of maximum bending moments and shear forces, resulting from these design approaches analysed using two constitutive models are presented, demonstrating the variation in the design outcomes which will result in different designs when the different codes are followed. The approach provided in AS 5100.3 where the analysis is conducted using unfactored loads and soil properties and then the effects of action are factored, seems more appropriate, in comparison to the other approaches. Further, design optimisation is possible using reliability-based methods to arrive at the appropriate factors in the design and achieve a more sustainable safe and reliable design.