Citation

Ng CWW, Lu H. Can. Geotech. J. 2014; 51(2): 173-183.

Copyright

(Copyright © 2014, National Research Council of Canada)

DOI

10.1139/cgj-2012-0452

PMID

unavailable

Abstract

Any tunnelling process inevitably induces changes in stress in the ground and may adversely affect nearby pile foundations. The interaction between tunnelling and an existing pile has been investigated by researchers and a certain amount of fundamental understanding has been gained. However, the effects of different tunnel excavation sequences on an adjacent pile remain to be understood. In this paper, a series of three-dimensional centrifuge model tests and numerical back-analyses were carried out to investigate the effects of construction sequence of twin tunnels on an existing pile in dry sand. Two tunnelling sequences were investigated: (i) a sequence involving tunnelling near the pile toe followed by tunnelling near the mid-depth of the pile shaft (i.e., test TS); (ii) sequence involving tunnelling near the mid-depth of the pile shaft followed by tunnelling near the pile toe (i.e., test ST). The measured cumulative pile settlement was about 33% larger for tunnelling sequence ST than for tunnelling sequence TS. Due to different tunnelling sequences, the apparent losses of pile capacity were 40% and 29% for sequences ST and TS, respectively. Although the computed reductions in normal stress acting on the pile induced by twin tunnelling were almost the same in tests TS and ST, tunnelling near the pile toe induced a larger decrease in the end-bearing and shaft resistances at the lower part of the pile in test ST than in test TS. In contrast to the measured pile head settlements, different tunnelling sequences had a limited effect on measured ground surface settlements and additional bending moments in the pile.

KEYWORDS: twin tunnelling, piles, construction sequences, soil-structure interaction, centrifuge modelling, dry sand


Tout processus de fonçage d'un tunnel entraîne inévitablement des changements des contraintes dans le sol et peut affecter négativement des fondations sur pieux à proximité. L'interaction entre le fonçage du tunnel et un pieu existant a été étudié par les chercheurs et ont permis d'obtenir une bonne compréhension fondamentale. Cependant, les effets des différentes séquences d'excavation d'un tunnel sur un pieu adjacent ne sont pas encore bien compris. Dans cet article, une série d'essais en trois dimensions en centrifuge et des analyses numériques inverses ont été réalisés pour étudier les effets de la séquence de construction d'un tunnel double sur un pieu existant placé dans du sable sec. Deux séquences de fonçage de tunnel ont été évaluées : (i) une séquence impliquant le fonçage près de la pointe du pieu suivi du fonçage près du milieu de l'arbre du pieu (appelé essai TS); (ii) une séquence impliquant le fonçage près du milieu de l'arbre du pieu suivi du fonçage près de la point du pieu (appelé essai...