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| Shaking table tests on longitudinal seismic response of shield tunnel through soft-hard stratum junction |
| ZHANG Jing，HE Chuan，GENG Ping，HE Yue，WANG Wei，MENG Li |
| (Key Laboratory of Transportation Tunnel Engineering，Ministry of Education，Southwest Jiaotong University，Chengdu， Sichuan 610031，China) |
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Abstract In order to investigate the seismic response of shield tunnels in the longitudinal direction cross the soft-hard stratum junction，a set of shaking table tests with geometric similarity ratio 1∶40 were carried out based on the equivalent longitudinal stiffness model. The spectrum of the acceleration response for both the strata and the tunnel structure were studied as well as that for the tunnel strain. The test results were compared with the numerically calculated ones. The results show that the spectrum properties of the acceleration response for the soft-hard junction stratum and the tunnel coincide with each other well，and both exhibit the double predominant frequency. As the depth of the soft-hard junction stratum decreases，the acceleration does not increase monotonically when the excitation earthquake frequency approaches the predominant frequency of hard stratum. The strain of the tunnel in the soft-hard junction stratum increases significantly and the maximum strain occurs on the soft side of this stratum. The enlarged longitudinal strain area of the tunnel distributes within the scope of 2.5–3.5 times of the tunnel diameter on both sides of the strata interface. The strain of the tunnel in each cross section arranges in a descending order as crown arch，inverted arch and side-walls. The strain difference between the crown and inverted arch as well as between the side-walls increases obviously compared to that in the uniform stratum. The soft-hard stratum junction not only enlarges the longitudinal internal force of the tunnel but also alteres its longitudinal bending direction.
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2017, Vol. 36 
