Abstract
This paper presents an approach that enables the specific characteristics of a primary tunnel lining implemented using numerical modelling to be taken into account during its design. According to the fundamental principles of the New Austrian Tunnelling Method, the primary lining undergoes time-dependent deformation, which is determined by its design. The main design element is shotcrete, which, shortly after its application, interacts with the surrounding rock mass and steel arch frame. The primary lining ensures the equilibrium stress–strain state of “rock mass–tunnel lining” during excavation. The structural interaction varies depending on the hardening of the shotcrete, the rheological properties of the rock mass, and other factors. The proposed approach uses the Homogenisation software application, which was developed by the Faculty of Civil Engineering at the Department of Geotechnics and Underground Engineering of the VSB—Technical University of Ostrava. This software allows the heterogeneous structure of the lining to be considered by replacing it with a homogenous structure. The parameters of the homogeneous primary lining, which take into account the steel reinforcement elements and the time-dependent property of the shotcrete, are included in numerical models.
Highlights
A major portion of current underground line construction in Central Europe is implemented partially or fully in accordance with the principles of the New Austrian Tunnelling Method (NATM).The tunnel lining based on the NATM principles is implemented with a double-shell tunnel lining consisting of a primary lining, as shown in Figure 1, and a secondary lining [1].The purpose of the primary lining is to temporarily secure the excavation and create suitable conditions in the rock mass for proper secondary-lining function
Correct application of the primary lining forms a load-bearing ring in the rock mass. It is important for the working characteristics of the primary lining to suitably respond to rheological processes occurring in the rock mass and allow certain deformations while preventing the development of critical deformations that may cause secondary impairment and loosening of the rock mass [1,2]
The driving stages are highly approximated, and depend on time factors, with the primary lining being applied after driving, and another section being excavated at the length of burden
Summary
A major portion of current underground line construction in Central Europe is implemented partially or fully in accordance with the principles of the New Austrian Tunnelling Method (NATM).The tunnel lining based on the NATM principles is implemented with a double-shell tunnel lining consisting of a primary lining (temporary), as shown in Figure 1, and a secondary (definitive) lining [1].The purpose of the primary lining is to temporarily secure the excavation and create suitable conditions in the rock mass for proper secondary-lining function. The primary lining allows partial release of the original stress in the rock mass in the form of radial deformations, resulting in improved utilisation of the shear strength of the massif and ensuring that the optimum load on the secondary lining is achieved. Correct application of the primary lining forms a load-bearing ring in the rock mass. It is important for the working characteristics of the primary lining to suitably respond to rheological processes occurring in the rock mass and allow certain deformations while preventing the development of critical deformations that may cause secondary impairment and loosening of the rock mass [1,2]
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