Centrifuge modelling of the impact of mechanised tunnelling on piled foundations using a miniature TBM

The ongoing urbanisation of cities has placed ever-increasing demands on their transport networks, resulting in a growing development of the underground landscape within urban areas. This means that the construction of new tunnels often occurs close to existing piled structures. The majority of tunnelling projects are currently being carried out using tunnel boring machines or TBMs. Understanding the stress relief and soil deformations taking place in the soil mass around the tunnel boring machine is key to analysing the complex problem of tunnel-soil-structure interaction. The cost and complexity associated with field monitoring of tunnelling projects in the urban environment make modelling the advancement of a TBM in a geotechnical centrifuge an attractive proposition. In this research, a miniature EPB TBM was developed for use in the Turner beam centrifuge at the University of Cambridge aiming to simulate the impact of tunnel construction on existing piled foundations. The model TBM simulates most features of real-life tunnelling machines including cutterhead overcut, shield tapering, and the use of a screw conveyor to extract soil from the excavation chamber in a controlled manner. The present mini-TBM can simulate the construction of a 4 m diameter prototype tunnel at 50g. Two centrifuge tests were conducted to simulate the mechanised tunnelling process in greenfield conditions. The first test was aimed at calibrating the optimal set of operating parameters necessary to achieve a volume loss of 2.5%, whereas the second one focused on understanding the mechanisms taking place around the model TBM in a controlled environment. The progressive development of the settlement trough was observed, and the final transverse settlement profile was similar to the commonly employed Gaussian prediction. A threedimensional FE model was constructed to replicate the operation of the mini-TBM at high gravity and to get more insights into the physical processes occurring around the model TBM. Four other centrifuge tests were carried out to investigate the effects of mechanised tunnelling on piled foundations. Different layouts of single piles and pile groups were considered. The settlement response of piles to tunnelling was first investigated, and a methodology for producing simple design charts for the estimation of pile settlements was proposed. The load transfer mechanism in single piles was then examined, together with the load redistribution within piles in groups. The rotation of the pile cap in the tunnelling direction was found to govern the load redistribution pattern within piles. Finally, the tunnelling-induced transverse and longitudinal bending moments along piles were investigated. Comparisons were made between the behaviour of single piles and their equivalent in groups. The work conducted in this thesis represents a significant technological breakthrough, enabling the realistic simulation of tunnelling-induced soil-structure interaction, and establishes a solid foundation for future advancements in this field.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Alagha, Ahmed S N

Advisors dc:contributor.advisor

• Viggiani, Giulia
• Haigh, Stuart

• Centrifuge Modelling
• FE Modelling
• Mechanised Tunnelling
• Miniature TBM
• Pile Foundations

Licence

• https://www.repository.cam.ac.uk/bitstreams/d249724d-692c-4e24-9ea6-9e0ef2533f9c/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.123366

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/392740