## 6 Conclusions  
In this paper, the dynamic response characteristics (acceleration, corresponding spectrum, and strain) of the tunnel under normal fault creep-slip and subsequent seismic excitation were conducted by shaking table tests. The effect of the rubber-sand isolation layer was studied by the test results and validated by numerical simulation. Furthermore, the influence of the isolation layer parameters (length, damping ratio, and elastic modulus) on the dynamic response of the tunnel is discussed. The following conclusions were drawn:  
(1) The results from the shaking table model tests indicated that seismic excitation in different directions causes different dynamic response characteristics in the tunnel. The rubber-sand isolation layer can slightly reduce the peak acceleration of the tunnel in the fault and absorb the seismic wave energy.  
(2) Under normal fault creep-slip and subsequent seismic shaking, the strain in the lining invert is greater than in the lining crown. The damage of the tunnel is caused by a combination of permanent strain and seismic strain. The rubber-sand isolation layer can effectively reduce the permanent strain at the tunnel lining invert and crown.  
(3) Based on the numerical analysis, the peak strain of the lining invert is maximum at the creep-slip cross-section of the fault, and the influence range of the fault does not vary with the parameters of the isolation layer.  
(4) As the length of the isolation layer increases, the peak strain in the lining decreases rapidly at first and then tends to become stable. The length of the isolation layer with three times the width of the fault (the influence range of the fault in this study) may be the optimal parameter.  
(5) The damping ratio and the elastic modulus of the isolation layer, which are influenced by the rubber content, have an essential effect on the strain response of the tunnel lining invert. A proper increase in the rubber content in the rubber-sand isolation layer can provide favorable mitigation conditions for the tunnel during normal fault creep-slip and subsequent seismic excitation.  
The effect of the rubber-sand isolation layer on the dynamic response of the tunnel was initially studied through shaking table experiments and numerical simulations. In the next phase, we will pay more attention to dynamic mechanical experiments in the rubber-sand isolation layer to further study the mechanism of the rubber-sand isolation layer.  
Conceptualization, S.P. and L.F.; methodology, S.P.; software, Y.L., Y.Z. and Z.X.; validation, Y.Z., S.P. and Z.X.; formal analysis, Y.L., Y.Z. and Z.X.; investigation, S.P.; resources, G.C.; data curation, Y.Z. and G.C.; writing--original draft preparation, Y.L. and Y.Z.; writing--review and editing, S.P., Y.L. and G.W.; visualization, L.F.; supervision, S.P.; project administration, S.P., L.F. and G.W.; funding acquisition, S.P., L.F. and G.W. All authors have read and agreed to the published version of the manuscript.  
The research was funded by the National Natural Science Foundation of China (Grant No. 52174100 and No. 51674287), and the National Science Foundation of Hunan Province, China (Grant No. 2021 JJ30834).  
Not applicable.  
The data that support the findings of this study are available upon request from the authors.  
The authors declare no conflict of interest.