Ground-Shotcrete Interaction of NATM Tunnels with High Overburden

According to the New Austrian Tunneling Method (NATM), after excavation of a cross section of a tunnel, shotcrete is applied onto the tunnel walls, constituting a thin flexible, closed shell. Deformations, as well as the loading of the lining, are continuously monitored during construction, serving as input for the decision making process following the closed control cycle “excavation–monitoring–parameter adaptation–excavation”. The objective of this control cycle is to optimize the tunneling process with respect to cost, crew safety, and long-term tunnel stability. In this paper, questions related to this optimization process are addressed, dealing with the influence of driving parameters and changes in the in situ geological and geotechnical conditions on the deformation and loading of the shotcrete lining. Based on realistic material models for shotcrete and ground, axisymmetric analyses, allowing for consideration of the three-dimensional nature of the tunnel excavation, were performed. The assumption of axisymmetry represents a good approximation of the static conditions of tunnels with high overburden. The obtained results are presented in dimensionless form, providing new insights into the complex ground-shotcrete interaction in NATM tunneling.