Shixiong XU

Study on construction condition for construction loads of shield tunnel by Shield Kinematic Model

Supervisor  Mitsutaka SUGIMOTO

Today, shield is controlled by expert system. But this system is based on empirical rules and does not have a theoretical background, since there are many unknown properties, such as ground properties, external forces and construction loads. To overcome these problems, the kinematical shield model considering the ground-shield interaction is required. Nowadays, underground structures in cities are very congested, therefore, shield tunnel has been constructed in deep underground with sharp curve. Furthermore, the stress in segment due to construction loads is larger than before, since segment has been wider and thinner for saving the cost.
Therefore, this study aims to examine the effect of construction conditions, such as segment length, curve radius, and front and rear length of shield machine, to construction loads by the Shield Kinematic Model. In the study, referred to the construction site of Nihon Embankment, the ideal data are set. 
Numerical experiment is made by the following consequence. Firstly, the articulated angle and the area cut by copy cutter are calculated by geometric method. Secondly, jack thrust, F3r, moment around p axis induced by jack thrust, M3p , and moment around q axis induced by jack thrust are made as 0. F3r , M3p , M3q are calculated by the balance of force and moment. Then, the obtained value of F3r , M3p , M3q are inputted, and the simulation of shield behavior is made on the spot of sharp curve where the effect of construction loads are prominent.
 As a result, following conclusions were made.
1) Because the balance of forces is not considered when the controlling condition (articulated angle and over-cutting) is calculated by geometric method, shield becomes meandering (shift, rotation) periodically in the horizontal plane. The tail clearance is also varied in the same period.
2) Evaluation is made on the effect of construction conditions on construction load of shield machine.