Abstract

A research programme conducted at the University of Cambridge geotechnical centrifuge provided high-quality data on the interaction effects of open-faced tunnelling beneath non-displacement piles in clay. This paper presents details of the novel centrifuge package, including the reinforced composite piles used to measure loads during the centrifuge tests. Attention is particularly drawn to the importance of temperature compensation and the corresponding effect on the model piles. Results from maintained pile load tests conducted in the centrifuge are presented; through photogrammetric techniques, these are compared with data from pile load cells. The results, also compared with analytical t–z power-law modelling of the soil stress–strain behaviour based on triaxial tests, illustrate the importance of modelling the full history of both soil and piles prior to any subsequent tunnelling-induced loading. The experimental results of the simulated tunnelling tests on piles are presented and compared with simple analytical solutions in a companion paper.

Highlights

  • With over half of humanity living in urban areas, the demand on space and new transport infrastructure is unprecedented

  • The stress changes from such tunnelling activities result in soil movements that propagate through the soil and are eventually observed as settlement and horizontal displacements at the ground surface

  • Significant research has gone into the prediction and observation of the effect of these ground movements on buildings supported by shallow foundations (e.g. Burland, 1997; Potts & Addenbrooke, 1997; Franzius et al, 2006; Farrell, 2010; Mair, 2011)

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Summary

INTRODUCTION

With over half of humanity living in urban areas, the demand on space and new transport infrastructure is unprecedented. Well-documented experimental data from centrifuge model tests of tunnelling beneath driven piles, as reported by a number of researchers including Jacobsz et al (2004), Marshall & Mair (2011) and Marshall (2012), showed significant pile settlements due to reduction in the pile base capacity caused by interaction of the tunnelling (causing stress relief) with the existing pile stress bulb. In order to provide high-quality data on the interaction effects of open-face tunnelling beneath non-displacement (predominantly friction) piles in clay, a research programme was conducted using the geotechnical centrifuge at the University of Cambridge (Schofield, 1980). In a companion paper (Williamson et al, 2017), experimental results of the simulated tunnelling tests on piles are presented and compared with simple analytical solutions

BACKGROUND
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