FEM Analysis of the Whole Construction Process of Super-Long Inclined Connecting Passage by Freezing Method

The ground freezing technology is usually used to improve the strength and stability of soil when excavating the subway connecting passage in coastal soft soil areas. Frost heave, stress concentration of segments and liners, thawing settlement etc. problems are great challenges in the construction process of freezing method. Based on the freezing construction method of a super long inclined connecting passage of Tianjin Metro Line 7, this paper uses ABAQUS software to establish a 3D sequential thermo-mechanical coupled finite element model to carry out numerical analysis of the whole process including active freezing period, maintenance freezing period and natural thawing period according to the construction sequence. The results show that for inclined connecting passage, the frost heaving and thawing vertical displacements of the ground surface are unidirectionally symmetric, and the stress distributions of the tunnel segment and the inclined connecting passage liner are asymmetric. During the excavation and support process, there are large stress concentrations in the middle of the opening side of the segment and the sharp corner of the inclined connecting passage liner. After the soil thaws, the concentrated stresses at the sharp corners of the inclined connecting passage decrease due to the release of frost heave pressure, as well as those at the corners of the connecting passage straight wall.