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Semi-analytical prediction of ground movements due to shallow tunnels in sand

Proceedings article published in 2015 by Andrea Franza, Alec M. Marshall ORCID
This paper is available in a repository.
This paper is available in a repository.

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Preprint: policy unknown
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Postprint: policy unknown
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Abstract

In engineering practice, tunnelling-induced ground movements are often described by empirical formulas. Recent research has shown that simple empirical relationships do not predict the change in settlement trough shape that occurs in sands as tunnel volume loss increases. In this paper, a closed-form solution is developed to assess the greenfield displacements around shallow tunnels in sand. An elastic analytical solution for incompressible soil is modified through a corrective term, which is a function of the spatial coordinates and tunnel volume loss. The elastic solution allows modelling of the tunnel deformation mechanism through a volume loss and ovalization term. The corrective term aims to account for the effect of non-linear behaviour and volumetric strains on the resulting settlement trough shape. One plane-strain centrifuge test performed on tunnels in dry silica sand is used to define a relationship for the tunnel deformation parameters (ground loss and ovalization) and to calibrate the coefficients of the corrective term. The results highlight the main effects of volume loss on the ground movement patterns. Furthermore, the outcomes illustrate that closed-form solutions developed for clay may not be applicable in sands. An expression to estimate vertical and horizontal displacements for shallow tunnels in sands is proposed, which may provide useful guidance to tunnel design engineers.