عنوان مقاله [English]
In this study, the expansion of the loosening zone at the top of horseshoe tunnels bored in layered soil has been studied. Two and three-dimensional finite element analyzes have been used. The effects of over-consolidation, changes in thickness and location of the soft soil layer have been evaluated in the form of the unstable zone concept on the extent of the loosening zone. Mohr-Coulomb (MC) and soft soil creep (SSC) models have been used to model the soil layers. Also, the comparison of the numerical analysis results of the plastic and consolidation analyses is provided. The results of this article show that the thickness of the unstable zone, the extent of its expansion in relation to the tunnel digging position, the surface building surcharge condition, the type of plastic or consolidation analysis and the over-consolidation condition of the soil generally change the geometry of the loosening zone in the tunnel crown. These changes include significant differences in the dimensions, pattern and expansion of soil loosening range.