GRAĐEVINSKO INŽENJERSTVO SA ASPEKTA DIMENZIONIRANJA PRIMARNE PODGRADE KOD IZGRADNJE TUNELA /CONSTRUCTION ENGINEERING FROM THE ASPECT OF DIMENSIONING PRIMARY SUBGRADE IN TUNNEL CONSTRUCTION

Abstract

The paper presents the principles of dimensioning the primary support in tunnel construction. In the process of tunnel construction, after the adopted excavation and support technology, the dimensioning of the tunnel structure is carried out in phases. When choosing the concept of tunnel construction, it is necessary to verify all phases in the formation of the support structure, with special attention to the quality of the rock mass and the pressures affecting the support structure, including the pressures of the structure itself, while adhering to regulations and technical standards. The goal of solving the stress-deformation problem of the tunnel structure is to prove its stability, which is carried out based on the principles of finding the state of stress, deformation, and displacement in the rock mass and the primary support of the tunnel for the observed cross-section. The relationship between the load-bearing capacity of the rock mass and the degree of relaxation is a key factor in the stability of the tunnel excavation. In the paper, this relationship is illustrated by applying the stability factor parameter of the tunnel (Ns). In numerical analysis, it is necessary to strive to adopt a value of λ that is close to the value for λcr, as this allows for the dimensioning of the support that will meet the needs of the dominant elastic response of the rock mass, or closest to the principles of NATM. The value of the λ-factor, which is used as input data for numerical analyses, is determined based on theoretical assumptions and assessments of the load-bearing capacity and quality of the rock mass. Certainly, the most realistic assessment is achieved through back static analyses using data from measurement profiles in the field.