Prediction and Control of Ground Deformations for Mechanized Tunneling in Clays with Mixed Face Conditions

Abstract

This paper describes a new methodology for predicting and controlling ground movements for a tunnel that traverses an interface between two clay layers of contrasting shear strength and stiffness. We use non-linear finite element analyses to investigate effects of face pressure on tunnel face stability and steady state ground surface deformations. This leads to a series of design charts linking soil properties (undrained shear strength and stiffness), stratigraphy (layer interface), tunnel cover depth and mechanized control parameters (face and grout pressure). The methodology has been validated for a recent case study where EPB tunnels traverse an interface between stiff clay (Old Alluvium) and soft, Marine clays. The proposed methodology successfully uses the measured face pressures to predict ground movements for these mixed face conditions. Further generalization of the method is now needed to represent mixed face conditions with contrasting permeability.