Key features of numerical models for the FE-simulation of deep tunnel advance by the NATM

Abstract

In the present work, important aspects of time-dependent nonlinear 3D finite element (FE) models for deep tunnel advance by the New Austrian Tunneling Method(NATM), characterized by repeated sequences of excavation, securing, and idle periods, are discussed on the example of a 3D finite element model of a stretch of the Brenner Base Tunnel, which is currently constructed between Austria and Italy. Nonlinear material models are utilized for representing the surrounding rock mass and the shotcrete shell. Based on the finite element model, strategies for the efficient implementation into a parallel distributed memory numerical code are proposed. They are essential to achieve reasonable computation times for numerical simulations of tunneling based on large 3D FE models. In particular, the implementation of the construction procedure, parallel computing and communication specific details, and efficient linear solvers for the global equation system within the incremental-iterative Newton-Raphson scheme are addressed. Furthermore, possible extensions of the material models for rock mass and shotcrete, used in the 3D FE model, are presented. They concern (i) a gradient-enhanced model for transversely isotropic rock and rock mass, taking into account hardening and softening behavior and (ii) the extension of the shotcrete model to nonlinear creep and damage due to creep. The possible benefits of the model extensions in numerical simulations of tunneling by the NATM are discussed.

Keywords

NATM / Finite element model / Rock / Shotcrete / Damage-plasticity model