Name: Ryosuke IWATA

Thesis title: Numerical analysis on the behavior of primary lining around face in SENS

Supervisor: Mitsutaka SUGIMOTO

SENS, a new tunneling method adopted for the first time in the world during the construction of Sanbongihara tunnel on the Tohoku Shinkasen has been demonstrated to be a superior method of construction in terms of safety, construction workability, and economic efficiency. 
However, in the above project, cracking occurred in the longitudinal lining of the tunnel, and underground water furthermore observed to leak through the cracks. In future cases where the application of SENS in urban areas is considered, the problem of water leakage may pose a serious threat to the proper evaluation of such factors as ground subsidence and influence on neighboring structures, making it a point of great importance to reduce this as much as possible. It is considered that the cracking is due to the floating of the inner mold in the unconsolidated concrete of the primary lining as it separates from the shield machine.
In order to minimize the occurrence of cracks and build a more robust lining, it is necessary to understand the behavior of the inner mold and lining and the mechanism of cracking. However, with most previous studies on the analysis of the behavior of the inner mold and lining and the propagation of cracks, the tunnel construction process and construction conditions are not reflected in three dimensions. Therefore in this study, we have developed a three-dimensional analysis model that takes into account the construction process and construction conditions, factors understood to affect behavior of the inner mold and lining in SENS. The features of this analysis model are as follows:
(1) Whole circumference ground spring model: Lining is presented in a beam and spring model. Lining is modeled to be supported by ground springs acting normally along the entire circumference of the lining. 
(2) Evaluation of active earth pressure from the subgrade reaction curve: Active earth pressure is evaluated by presenting ground displacement and the coefficients of earth pressure as two hyperbolic functions in a subgrade reaction curve.
(3) Hardening process of the primary lining concrete: In situ cast concrete which is the lining in SENS begins to harden with passing of time. In order to present the hardening process of this lining in a phase analysis, the Young's modulus of concrete is set according to the elapsed time from when the concrete is first cast.
(4)Casting pressure of Concrete: Casting pressure of concrete is applied on the inner mold of unconsolidated concrete of the primary lining.
This analysis was conducted according to data from the construction project of the Yomogida Tsugaru tunnel and results compared with measurement results. As a result, the analysis value was observed to generally follow the same trend as the measured value and sufficient to express the construction conditions of SENS.