Rationale for choosing the methodology to determine the stress-strain state parameters of a tunnel during its cross-section expansion

Purpose. The purpose is to provide a rationale for choosing the methodology for determining the stress-strain state (SSS) parameters of tunnels during their cross-section expansion. The results of this justification, based on contemporary approaches to the stated problem, achieved the set objective. They provided a scientifically sound basis for selecting a methodology that most comprehensively reflects both the interaction within the “underground structure – surrounding rock mass” system and the specific technological features of expanding the running tunnel's cross-section. Methodology. Currently, the problem of determining the SSS of a running tunnel interacting with the surrounding rock mass, while accounting for its cross-section expansion, is addressed through three main approaches: analytical, experimental, and numerical. Selecting the methodology to determine SSS parameters in the case of subway tunnels with various orientations within the rock mass represents the first step in substantiating a rationale for the research. Analysing these methods to select the primary one for calculating the “underground structure – surrounding rock mass” system also reveals trends in the development of research methodology. Findings. During the justification of the methodology for determining tunnel SSS parameters, three main approaches to resolving this problem were identified: analytical, experimental, and numerical. A comprehensive rationale was performed for choosing the methodology to determine the stress-strain state parameters of tunnels during their cross-section expansion. A comparative analysis of the advantages and disadvantages of these various approaches proves that numerical analysis is the most adequate method for achieving the stated objective, as it allows for the most complete consideration of the expansion process features within finite element models. Originality of the obtained results lies in the development of a research approach adequate to the stated problem, which enables a highly accurate representation of the interaction within the “underground structure – surrounding rock mass” system and the process of running tunnel cross-section expansion. The numerical analysis methodology provides an enhanced approach that accounts for the working expansion stages, temporary and permanent lining components, and the properties of the surrounding rock mass. Practical value of this research consists in creating a finite element model that reflects the expansion technology of a running tunnel constructed using NATM, grounded in the theoretical principles of the chosen methodology. The developed model fully captures the stage-by-stage process of running tunnel expansion and the specific technological features of NATM technology, characterizing it as a tool that enables to research into the stress-strain state parameters in an expanding running tunnel.