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Details of Grant 

EPSRC Reference: EP/X024849/1
Title: Braced excavations: what about the corners?
Principal Investigator: Augarde, Professor C
Other Investigators:
Petalas, Dr A Coombs, Professor WM
Researcher Co-Investigators:
Project Partners:
AKT II Cementation Skanska Limited Laing O'Rourke Ltd
Oasys Ltd University of Southampton
Department: Engineering
Organisation: Durham, University of
Scheme: Standard Research
Starts: 01 May 2023 Ends: 30 April 2027 Value (£): 470,691
EPSRC Research Topic Classifications:
Ground Engineering
EPSRC Industrial Sector Classifications:
Construction
Related Grants:
EP/X024768/1
Panel History:
Panel DatePanel NameOutcome
07 Dec 2022 Engineering Prioritisation Panel Meeting 7 and 8 December 2022 Announced
Summary on Grant Application Form
When a new metro station or a deep basement are to be constructed in a city, a large hole in the ground is needed. The hole needs to be safe to work in and to allow access and very often the chosen solution is to support the sides of the large hole with a braced embedded retaining wall. These are substantial pieces of temporary works of considerable cost. Recent examples are the 230 long by 24 m wide by 23m deep excavation for the new Crossrail station at Paddington in London. An important feature of this form of construction is large props that span between the walls, to hold them up.

For those tasked with designing the prop size, location, number and the walls the key issues are prediction of ground movements adjacent to the excavation (which could negatively affect buildings) and propping forces (so that the right props can be used and while guidance exists for designers in some recent publications produced by the UK construction information organisation, CIRIA, coverage of the behaviour at excavation corners as regards both design issues is poor. There is substantial published research on the computational modelling of braced excavations but only in two-dimensions (i.e. s slice through a long wall), some of it validated against field data, however accounting for 3D effects as required for the analysis of corners is rare and insubstantial. Improving our understanding of the behaviour of these corners and how it is affected by soil behaviour, system stiffness, and prop loading will lead to (a) greater economy in propping schemes and (b) more certainty in the prediction of ground movements adjacent to corners, potentially reducing the accommodation works required to prevent damage to adjacent structures.

The programme of research proposed here comprises complex computational simulations of the construction of a braced excavation, taking into account differences in geometry, materials and sequences. The problem can only be properly tackled using a 3D model (unlike many other problems in geotechnical engineering) however even today, the computational tools we use struggle to deliver results quickly when we try to model in 3D. So, in this proposal we will be using a clever method where "reduced order models", (ROMs) will be made, using results from a relatively small set of the complex 3D models. A ROM is much easier to use and is generated by manipulation of a limited number of the high fidelity 3D simulations. From these ROMs we will derive results and prepare guidance for engineers designing braced excavations which will enable cheaper and simpler schemes to be used.

The researchers on the project come from Durham and Dundee Universities and are supported by a Project Oversight Group comprising key figures from the UK industry.
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