Movements of ground and existing structures induced by slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay

This paper presents a comprehensive study of field measurement of ground movements and displacements of adjacent existing structures induced by large diameter slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay. The evolution of displacements at six transverse monitoring sections against the distance of TBM cutterhead from corresponding instrumentations is characterized and interpreted in conjunction with recorded TBM tunnelling parameters. Measured results highlight that adjacent existing structures move almost synchronously along with ground except the magnitude, and stiffer structures can greatly resist deformation than pure soil does. The cast-in-place piles constructed between current tunnel and elevated bridge can effectively block the propagation of tunnelling-induced deformation. Results also show that the compensation effect of tail grouting on ground displacements is limited to the local areas which are close to the grouting position, and this effect attenuates as the distance from grouting position increased. The final "inwards" or "outwards" trend of surrounding soil relative to the tunnel relies on the injected grouting volume. The observation indicates that TBM tunnelling parameters at a transverse section can not only influence ground settlements there but also influence ground settlements ahead and behind this section along longitudinal direction to varying degrees. This longitudinal effect can be considered by introducing the impact coefficients of face pressure and tail grouting. The measured data of surface settlements along tunnel longitudinal axis and predicted ones using Loganathan-Poulos formula with and without considering this longitudinal effect are compared. The compared results indicate the longitudinal effect should be taken into account for the accuracy of prediction. The paper can provide valuable references for settlement prediction due to TBM tunnelling in clayey soil.