Undrained Seismic Stability of Dual Unsupported Circular Tunnels Subjected to Surcharge Loading

Undrained seismic stability of dual unsupported circular tunnels was investigated in this work using a self-developed code for adaptive finite element limit analysis. The so-called pseudo-static method was used to simulate the seismic effects during an earthquake. Accurate upper and lower bounds of seismic stability factor Ns were obtained by using an adaptive remeshing technique incorporated in the code. Comprehensive parametric studies of the problem variables, including the horizontal seismic coefficient kh, the relative spacing ratio S/D, the relative depth ratio H/D and the strength ratio gamma D/cu were performed to provide dimensionless design tables for practical uses. In addition, visualized results from AFELA were summarized to reveal how the failure mechanism of dual tunnels would evolve with varying problems variables. Numerical results showed that both the stability and failure mechanism of dual tunnels can be much affected by seismic effects which should be carefully considered for a reasonable design in earthquake zones.

Automated summary

This study investigated the undrained seismic stability of dual unsupported circular tunnels using an adaptive finite element limit analysis. Parametric studies and visualized results showed the significant impact of seismic effects on tunnel stability and failure mechanisms.