Evaluation of analytical methods to interpret ground deformations due to soft ground tunneling

Abstract

An in depth study was undertaken to evaluate the effectiveness of analytical solutions in describing ground movements induced by soft ground tunneling. The analytical solutions that were examined consider both isotropic and anisotropic stiffness parameters and were proposed by Pinto and Whittle (1999) and Chatzigiannelis and Whittle (2001) respectively. Computed ground movements were compared to field measurements from five published case studies of tunnels around the world that involved different excavation methods (open and closed face tunneling) and varying soil properties. A Least Squares Solution procedure has been employed in each case for selecting model input parameters that best describe the field data. The control study of the thesis involves the westbound tunnel of the Jubilee Line Extension project in London. The use of anisotropic stiffness parameters improved significantly the agreement with surface and subsurface field measurements. Moreover, the volume loss computed by the analytical solutions is significantly reduced comparing with previous published interpretations of volume loss that were based on empirical methods. The analytical solutions prove to be a very powerful tool for describing ground displacements induced by different methods of tunnel excavation through various soil types. They are practical, since they require minimal information on soil properties, while at the same provide a complete framework for understanding the relationships between the distribution of far-field deformations, construction methods and ground conditions.

(cont.) Pinto's proposed design method proved to be effective in selecting appropriate input parameters for most tunnel cases apart from the tunnels excavated in London Clay.