Foundation response to ground movements induced by tunnel excavation

In this study, continuum numerical approaches based on the two-stage method were developed to enable the efficient analysis of tunnelling-induced effects on shallow and deep foundations. These approaches were applied in the back analyses of well-documented field case histories and centrifuge experiments to investigate in detail the response of foundations to tunnel excavation. A numerical program known as PRAFT was developed to model incrementally the effects of an advancing tunnel excavation on single piles, pile groups and piled rafts. Greenfield displacements are critical input parameters in a two-stage analysis of tunnel-structure interaction. An improved empirical method for the prediction of near-surface tunnelling-induced horizontal displacements in fine-grained soils was developed from the back analysis of field and experimental measurements. The focus of vectors of tunnelling-induced displacements was found to be a function of depth and the transverse offset distance from the tunnel axis. This method has shown to give more realistic values of horizontal displacements and horizontal ground strains, which are often under-predicted by current empirical and analytical methods. The crossing of the Grosvenor Bridge by an earth pressure balance tunnel boring machine (TBM) was back-analysed. Different soil-structure interaction approaches of various complexity including continuum-based elastic analyses, plane-strain finite element analysis and three-dimensional finite element analysis were compared. The continuum approaches were able to produce reasonable results in good agreement with more advance analyses and field measurements in terms of the salient response of the arch bridge, which was the tilting of the bridge piers and closing of the span above the tunnel. The continuum method was also applied to study numerically the full-scale field trial of instrumented piles at a test site at Dagenham under the Channel Tunnel Rail Link project. The development of surface settlement, transient subsurface heave and additional settlement due to the cessation of tail-skin grouting were considered in the analysis. It was found that realistic stress paths and induced axial forces consistent with field measurements could only be obtained by considering the "path-dependent" nature of the loading and unloading process. Finally, the results of a series of centrifuge experiments using a miniature TBM, which was able to simulate actual soil excavation by a rotating cutterhead and its effects on foundations in-flight, were reviewed and reproduced numerically. The continuum analyses predicted the settlement, differential settlement, bending moment and load redistribution of single piles and pile groups of different lengths, offset distance and configuration, with good general agreement with centrifuge measurements. With the PRAFT program validated against field and centrifuge measurements, a parametric study was carried out to produce a design chart for quickly estimating the tunnelling-induced settlement of a single pile and pile groups relative to the greenfield settlement trough. It was found that the ratio between pile and greenfield settlements would be about two on the tunnel centre-line, reducing to about unity at the inflection point of the transverse settlement trough. Using the above numerical results, suggestions were made on the possible optimisation and planning of future centrifuge tests involving the mini-TBM to investigate foundation response to tunnelling. Emphasis was also placed on the need for carrying out subsurface displacement measurements so that the mechanism of ground displacements caused by TBM excavation is understood more thoroughly.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Wong, E.K.L

Advisor dc:contributor.advisor

• Viggiani, Giulia

• foundations
• numerical analysis
• tunnelling
• tunnelling-induced displacements

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b3160857-a2c1-4582-8187-7ef4af3052a2/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.115578

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/379499