Modern geotechnical codes of practice and new design challenges using numerical methods for supported excavations

• Main Author: Katsigiannis, Georgios
• Published: University College London (University of London) 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.747017

Eurocode 7 (EC7), which is the geotechnical engineering design standard in Europe, introduces the concept of partial safety factors and distinguishes between Serviceability Limit State (SLS) and Ultimate Limit State (ULS). While EC7 allows the use of Finite Element Methods (FEM) for ULS, there is limited guidance in a number of issues. The thesis focuses on a number of constitutive models of increasing complexity and both the characteristic and design values of the model parameters are derived for the London Clay and a soft Marine clay. The challenges associated with factoring the undrained shear strength when using total and effective stress parameters are discussed. The use of FEM for ULS design of supported excavations, is highlighted using simple excavation examples and two deep excavation case histories; the Moorgate Crossrail Station and the Exhibition Road Building of the Victoria & Albert Museum. The different factoring combinations and strategies, required by EC7, are compared in terms of the calculated design internal structural forces, illustrating that the use of more advanced models can have significant advantages. Moreover, comparisons are made between the design prop loads calculated from the FEM and a number of empirical methods. The HYD limit state, as described in EC7, relates to the upward flow of water through the soil towards a free surface. The HYD verification, using FEM, can be performed with two approaches; the soil block approach by calculating the equilibrium of a rectangular soil block and the integration point approach by checking that the equilibrium is satisfied at each integration point. Thorough comparisons between the two approaches using benchmark geometries illustrate the benefits of using more advanced approaches for such stability verifications.