Modeling Ground-Shell Contact Forces in NATM Tunneling Based on Three-Dimensional Displacement Measurements

Based on an advanced micromechanics-based nonlinear creep model for shotcrete and thin shell kinematics, measured displacement data are first converted into in-plane stress fields throughout a shotcrete tunnel shell driven according to the New Austrian Tunneling Method (NATM). Subsequently, the partial differential equations for the local force equilibrium in the cylindrical coordinate directions are solved for out-of-plane shell stresses, inclusive of the tractions at the ground-shell interface. Results obtained for an NATM-tunnel driven through clayey ground at moderate depth show that the maximum shear tractions at the ground-shell interface may even exceed the maximum normal tractions (ground pressure). At the same time, even a young top heading tunnel shell may act as an arching thrust. The authors regard this method as a further step in the continously refined of interpretation of displacement measurements stemming from tunnel monitoring systems for the NATM, on a well-defined mechanical basis. This results in two structural models for top heading excavation stages, which might have the potential to support NATM predesign activities in the future. DOI: 10.1061/(ASCE)GT.1943-5606.0000791. (C) 2013 American Society of Civil Engineers.