Comparative Analysis of the Numerical Model and Geodetic Measurements of the Settlement in the Kobilja Glava Tunnel

Abstract

This paper presents a comparative analysis of the settlement of the Kobilja Glava tunnel structure, using three-dimensional numerical modeling and geodetic monitoring during construction. The numerical model, developed in the Plaxis 3D software package, included all excavation and support phases, with rock mass parameters defined based on RMR classification and conversion of Hoek-Brown parameters into the Mohr-Coulomb form. The primary lining was modeled using plate elements, while anchors were represented as embedded elements with equivalent elastic modulus.
Geodetic measurements were carried out continuously, with measurement points positioned at the tunnel crown, sidewalls, and the bench, providing actual convergence values. Comparison between the numerical model results and geodetic measurements revealed discrepancies ranging from 18% to 24%, with the largest deviations recorded at a distance of 24 m from the excavation face. Statistical data analysis (RMSE ≈ 3.71 mm; σ ≈ 1.21 mm) confirmed the presence of a systematic prediction error, but also the stability of deviations across the analyzed points.
The results confirm the technical validity of the applied model and the designed support system, while emphasizing the need for dynamic updating of numerical models in accordance with field data. This further reinforces the implementation of the observational method as a reliable approach under real tunneling conditions.