Abstract: The failure mechanism of double-arch tunnels due to voids behind lining and the relevant maintenance technology remains scarce. As a result, a similar model test and finite element simulation are performed to investigate earth pressure distribution, structural safety, and failure laws as the location and size of a void behind lining change. The results show that: (1) Due to a void behind the lining, the earth pressure acting at the spandrel inside is larger than outside, and the largest value occurred at the en echelon area. (2) A change in the void location causes significant differences in the distribution pattern and propagation law of cracks at the crown and haunch of the tunnel on the same side of a void; however, it has little effect on the bottom of the double-arch tunnel. (3) When there is a void behind the central wall, the crown's minimum safety factor appears, and the crack with the greatest area appears earlier than in the other cases. (4) As the size of the void at the crown increases, the lining at the arch connected with the central wall is prone to cracking, resulting in serious failure. The angle of the void has a greater influence on lining failure than the height of the void. These cracks appear earlier as the void angle increases, on both sides of the void and at the left arch feet. The findings revealed the distribution law and process of crack propagation in double-arch tunnels caused by changes in the location and size of voids behind the lining. The large voids detected behind the linging of double-arch tunnels should be grouted timely.

Key words: double-arch tunnel, structural failure; model test, void behind lining