تقاطع گذرگاه ها و تونل های دوقلو
Abstract
1. Introduction
2. Cross passages in twin tunnels
3. Test design
4. Test results and discussion
5. Comparisons between test results and analytical results
6. Conclusions
Acknowledgements
References
Abstract
The abrupt structural change at the intersection of cross passage and twin tunnels is a potential risk when earthquakes strike. This paper addresses the seismic responses of the cross-passage intersection by shaking table tests. Test data from six cases are presented, where white noise and synthetic earthquake motions are adopted. Discrepant responses between the cross passage and the twin tunnels are described by acceleration data. The extent of discrepancy is quantified statistically. Influence of this discrepancy is evaluated in two directions: dynamic strains of the linings in the transverse direction and circumferential-joint extensions in the longitudinal direction. Since the earthquake-induced dynamic strains are relatively small, they are considered as an insignificant factor. However, there are considerable circumferential-joint extensions near the cross passage. Two simplified models are proposed to estimate the joint extensions in a pseudo-static way. Each model is corresponding to a unique pattern of longitudinal deformation caused by the discrepant responses of the intersection. Test results are compared with analytical results.
Introduction
It is mandatory to construct cross passages when the length of twin tunnels reaches certain limits. The cross-passage intersections should be treated with careful examinations regarding their seismic safety because of the structural nonuniformity. Since most analytical solutions are developed for seismic analyses of single cross-sections or regular tunnel lines [1,2], numerical modelling becomes the most frequently used method to address the seismic responses of cross passages. Jiao and his co-workers [3] assessed the seismic effects of cross passages on Qianjiang River Tunnel by finite element method. Their results indicate that cross passages affect longitudinal seismic responses of the main tunnels significantly. Zhang [4] modelled the West Yangtze Road Tunnel in Shanghai by multi-scale method. Tunnel linings near the cross passages are described as ‘local hot-spots with stress concentration’ for the elevated integral axial forces and longitudinal bending moments. Further comparison shows that the cross passages only have minor influence on vicinal transverse cross sections of the main tunnels. Both studies point out that seismic responses of the main tunnels are aggravated near the cross passages, especially in the longitudinal direction. Yet, neither of them provides further elucidation on this matter. Another approach to study the seismic behaviors of tunnels is by model tests. Shaking table tests [5–۹, ۲۶] and dynamic centrifuge tests [10–۱۲] have been conducted, but the test objects are either single cross sections or straight tunnel linings. The intersection of cross passage and twin tunnels is scarcely mentioned. One relevant shaking table test was carried out by He [13].