Narrow Results

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 $N_s$ were obtained by using an adaptive remeshing technique incorporated in the code. Comprehensive parametric studies of the problem variables, including the horizontal seismic coefficient $k_h$, the relative spacing ratio $S$/$D$, the relative depth ratio $H$/$D$ and the strength ratio $\gamma D$/$c_u$ 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.