Experimental Investigation on Flexural Behaviors in Framed Structure of PST Method
Existing underground pipe jacking methods use a reinforcing rod in a steel tube to obtain structural stiffness. However, some problems such as inconvenience of works and expensive materials resulted from limited working space and reinforcing works are existed. To resolve these problems, a new pipe jacking method, namely PST (Prestressed Segment Tunnel) method, was developed which used joint to connect the steel segment and form erection structure. For evaluating the flexural capacity of the PST method structure, a experimental test was conducted. The parameters considered in the test were span-to-depth ratio of segment, diameter of steel tube at the corner, prestressing force, and welding of joint. The flexural behaviours with the effect of load capacity in serviceability state according to different parameters were examined.. The frame with long segments could increase flexural stiffness and the specimen with large diameter of concave corner showed excellent resistance ability to the negative moment. In addition, welding of joints increased the flexural capacity. Keywords—PST method, Pipe jacking method, Flexural behavior, Prestressed concrete.
Deformation behaviour of tunnel face reinforced with longitudinal pipes—laboratory and numerical investigation
This paper presents the results of laboratory and numerical investigations on the deformation behaviour of tunnel face reinforced with longitudinal pipes. A series of reduced-scale model tests as well as 3D finite-element analyses were carried out with particular emphasis on the effects of reinforcement parameters such as density (number), length and stiffness of reinforcements on the face deformation behaviour. The results of the present study indicate among other things that the face reinforcement technique can significantly reduce not only face deformation but also ground surface settlements, suggesting that the face reinforcing technique can be effectively used as a positive means for ground movement control during urban tunneling. The study illustrates that the reinforcing effect is significantly influenced by the manner in which the reinforcements are distributed, and that there exists a critical value of each reinforcement parameter from which maximum reinforcing effect can be derived. Implications of the findings from this study are discussed in great detail.
Extrusion movements of a tunnel head reinforced by finite length bolts—a closed-form solution using homogenization approach
An analytical model on the general behaviour of a tunnel head, reinforced by finite length bolts is proposed. This model is based on the homogenization method and spherical symmetry assumption. Despite its simplicity, and in consequence its limits of validity, it does allow a quick estimation of the key design parameters: frontal displacement, extension of decompressed zone, ground stresses and bolt tension, and constitutes thereby a very useful and handy tool for design engineers. In particular, the influence of the reinforcement length, as well as other important design parameters, are studied by the proposed model. The charts resulting from the parametric studies are directly applicable. Otherwise, the comparison to a 3D numerical model is also presented in this paper. The first results provide the validation of the analytical solution, at least in terms of average extrusion movements. Copyright © 2000 John Wiley & Sons, Ltd.