Prediction of the stress-strain state and stability of tunnel face at the intersection of disturbed zones of the soil mass

The article presents a numerical solution of the spatial elastic-plastic problem of determining tunnel face stability at the intersection of disturbed zones of the soil. The relevance of the study is related to the need to take into account the zones of disturbed soils when assessing the face stability to calculate the parameters of the support. Based on the finite element method implemented in the PLAXIS 3D software package, the design of a finite element system "soil - disturbance - tunnel face support" and modeling of the intersection of the disturbed zones of the soil were performed. To assess the stability of soils, deformation and strength criteria are taken. The deformation criterion is expressed by the value of the calculated displacement of the tunnel face surface, and the strength criterion - by the safety factor until the maximum values of the stress state are reached according to the Coulomb - Mohr criterion. The results of the study are presented in the form of histograms of the safety factor dependences on the distance to the disturbance at different bending stiffness of the tunnel face support structure, as well as the isofields of deformation development. The parameters of rockfall formation in the tunnel face zone at the intersection of zones of disturbed soils were determined. The local decrease in strength and deformation properties in the rock mass along the tunnel track should be taken into account when assessing the stability of the tunnel face and calculating the parameters of the sup-port. Within the framework of the constructed closed system, a qualitative agreement of the simulation results with the case of a collapse in the tunnel face during the construction of the Vladimirskaya-2 station of the Saint Petersburg Metro was obtained.