Abstract
The installation and working test performance of four full-scale instrumented driven piles and their subsequent response to twin tunnels constructed below the pile bases are described. One pair was designed to be largely friction piles and the other pair end-bearing. Their locations relative to the new tunnels were carefully chosen to optimise understanding of pile responses at varying offsets from the centre-lines. The site conditions and the greenfield response to earth pressure balance machine tunnelling at the site were described in a companion paper that reported an expanding displacement field around the tunnels rather than the contracting fields usually observed. The field monitoring results indicated that, during construction, zones of influence existed around tunnels, where the ground and piles were subjected to different degrees and senses of relative vertical displacement. Redistributions of load along the pile lengths occurred as the tunnel boring machines approached, passed beneath and continued beyond the pile bases; lateral pile deflections and bending moments were also induced. Based on the results from this field study, implications for the capacity of existing piles (and design of new piles) subjected to tunnelling-induced movements are assessed for cases of expanding and contracting displacement fields.
Highlights
The subject of tunnelling near piled foundations has received particular attention during construction planning of London’s Jubilee Line Extension (JLE), Amsterdam’s North–South line, the Channel Tunnel Rail Link (CTRL) and, more recently, London’s Crossrail
These responses indicate that earth pressure balance machine (EPBM) tunnelling is very efficient in minimising differential displacements ahead of the face but a sudden increase occurs once the tunnel boring machine (TBM) face is directly beneath the pile
IMPLICATIONS FOR DESIGN PRACTICE Prediction of pile settlement due to tunnelling From the results of this study it is evident that zones develop around an EPBM when tunnelling in London Clay, similar to those presented in previous studies (e.g. Kaalberg et al, 1999; Jacobsz et al, 2001), in which pile head and ground surface settlements can be correlated
Summary
The subject of tunnelling near piled foundations has received particular attention during construction planning of London’s Jubilee Line Extension (JLE), Amsterdam’s North–South line, the Channel Tunnel Rail Link (CTRL) and, more recently, London’s Crossrail. Two notable exceptions are the Heinenoord full-scale trial near Rotterdam (Kaalberg et al, 1999) and the study carried out by Coutts & Wang (2000), who reported field results from instrumented piles subjected to tunnelling-induced movements as part of the North–East line project in Singapore (see Pang et al, 2006). Twin tunnels through both Holocene deposits (layers of soft clay and peat) and Pleistocene dense sand. These field observations indicated that pile settlements can be grouped into three categories depending on the position of the pile toe relative to the tunnel axis (Kaalberg et al, 1999). Few comprehensive records of the greenfield ground response to EPBM tunnelling in London Clay exist and so this formed an essential component of the study
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