Prediction and interpretation of ground movements due to tunneling in stiff clay and impacts on adjacent structures

Abstract

Construction of large diameter tunnels is frequently accomplished by closed face tunnel boring machines (TBM) using a combination of face pressure and grouting around the precast lining in order to limit ground movements and potential damage to overlying structures. This thesis analyzes monitoring data from the Crossrail project involving twin tunnels construction using Earth Pressure Balance (EPB) machines in London Clay. The research focuses on the 'greenfield' response during tunnel excavation beneath Hyde Park. Far-field measurements of surface and subsurface ground movements were interpreted using 2D finite element analyses using a range of constitutive models with parameters calibrated to non-linear stress-strain properties measured in high quality laboratory tests on London Clay. The analyses optimize three input parameters corresponding to boundary deformations around the tunnel cavity, using a least squares fit to the measured ground movements. The results for the first tunnel (WB) show that even simple soil models are able to achieve good agreement with far field ground deformations, while more complex models (MIT-Si) can represent accurately movements occurring much closer to the tunnel lining and hence, provide a more reliable guide to deformation sources at the tunnel cavity. The study also shows how ground movements induced by the second (EB) tunnel were influenced by proximity to the completed WB tunnel. The results provide a comprehensive view of the ground movement pattern and a useful framework for understanding how ground response is linked to EPB control parameters that can be investigated using 3D finite element models. Comparisons with data from prior open-face shield construction of the Jubilee Line Extension (in similar ground conditions) show that there are pervasive differences in the magnitudes and cavity deformations modes associated with different methods of tunnel construction. The current analyses of soil-structure interaction consider the measured deformations of a concrete-framed structure, Avenfield House, caused by the twin Crossrail tunnels. The thesis proposes a simple elastic shear beam model of the structure and assumes that the cavity deformation parameters are uncoupled from the presence of the structure. The results demonstrate that deformations of the structure can be predicted using information from the greenfield ground response.