Analysis of SENS's lining behavior at shallow overburden

Mitsutaka SUGIMOTO

In the case of SENS, the primary concrete lining is installed to the space between ground and inner mold continuously. Since the primary lining is a fresh concrete, the inner mold tend to move upward due to buoyancy. After that, the primary lining becomes harden, and the earth pressure begins to act. Through three-dimensional behavior of inner mold and concrete installation, it is considered that effective earth pressure will be changed. Therefore, to estimate the earth pressure for the design of inner mold and primary lining, an analytical model, which can simulate the interaction among the ground, inner mold and primary lining, is necessary, taking account of three-dimensional and sequential behavior of inner mold.
The current design method for SENS can not express the stress redistribution in the tunnel axis direction due to the three-dimensional and sequential behavior of inner mold. In fact, in the load-bearing mechanism model, effective earth pressure is partially reduced to fit the calculated sectional force to measured one, while this mechanism has not yet been theoretically clarified. Besides, in the 3D FEM, which models tunnel and ground, it is difficult to simulate the change of effective earth pressure by the relative displacement among the excavation surface of the tunnel, the inner mold and the lining, and the upward rigid displacement of the inner mold due to buoyancy.
This research, aim to make clear the behavior mechanism of the inner mold and primary lining, during the complicated construction process from concrete installation to stripping of inner mold. A three-dimensional and sequential analysis model for SENS was developed, taking into account the load conditions and the construction process. In addition, the validity of this model was examined, using the site data. Furthermore, through the parameter study on ground and construction conditions, the influence of each parameter on the lining behavior and its sectional force was discussed.

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