Effect of double voids behind lining on safety state of tunnel structures

The existence of multiple-voids behind the lining leads to a more complicated stress state of the tunnel structures, which can easily cause the structural cracking and directly affect the safety of the tunnel structures. Based on a two-lane highway tunnel with the IV-class surrounding rock, numerical simulations and model tests are performed to study the safety state of tunnel structures under the influence of double voids behind the lining. The results of numerical simulation indicate that the existence of the double voids significantly changes the distribution of the internal forces in the tunnel structures, and worsens the stress state of the structures. The increase of the range of the void leads to the decrease of the axial forces of the whole tunnel structures, and makes the bending moments of the tunnel structures near the two voids obviously increase. The safety factor of each cross section of the tunnel structures between two voids obviously decreases compared with that in the situation without void. And it presents the trend that the safety factors gradually decrease with the increase of the range of the void. The region between two voids is the key part for security evaluation and improvement of the tunnel structures. When the double voids exist behind the lining of tunnel shoulders, it has a larger influence on the structural safety factors than the situation that the vault and shoulder of tunnel have the voids behind the lining respectively. The effects of voids on structural safety factors obtained by model tests agree well with the results of numerical simulation, and the failure evolution processes of the tunnel structures affected by double voids are also acquired by model tests. The results obtained in this study may provide useful reference for studying the failure mechanisms and safety control techniques of tunnel structures with voids behind the lining.