Keita IKEDA

Development of Analysis Method on Vertical Circular Tunnel by Pipe Jacking Method and its Application

Mitsutaka SUGIMOTO

When a road is constructed in underground by shield tunnelling method, the enlargement of underground opening is necessary at the connection part of a main tunnel and a lamp tunnel. For this purpose, a vertical circular tunnel by the pipe jacking method is under plan. However, since there are no case records on the circular tunnels in a vertical plane by the pipe jacking method, its feasibility should be examined using a numerical analysis and a model test. Therefore, this research aims to develop the analysis method on the vertical circular tunnel by the pipe jacking method, using a simple two-dimensional model, as a first step of the above-mentioned examination. 

First, the required thrust force at the entrance, which provides the required residual thrust force at the face, was determined for each installation angle of steel box. Next, to examine the influence of some construction conditions on the behavior and the sectional force of the steel box, a parameter study is carried out using the obtained thrust force at the entrance from the above study, taking the stiffness of interface element in normal direction, the friction coefficient of interface element in shear direction, the overcutting distance, and the elastic Young�fs modulus of ground as variables. 

Furthermore, in the case of the two-dimensional model and a stiff soil, the self-weight of the soil above the vertical circular tunnel is mainly supported by the ground outside the circular tunnel, then it is expected that stress concentration appears in the neighboring ground around the tunnel entrance. But actually, the self-weight of the soil mass above the vertical circular tunnel is also supported by the ground at both sides of the steel box, so the stress concentration in the ground by the two-dimensional model is considered to be excess. Therefore, a correction factor on the stress concentration around the tunnel entrance from the two-dimensional analysis to the three-dimensional analysis was proposed.

As a result, it was confirmed that the proposed analysis model can calculate the behavior and the sectional force of the vertical circular tunnel by the pipe jacking method reasonably. Also a correction factor on the stress concentration around the tunnel entrance from the two-dimensional analysis to the three-dimensional analysis was proposed.