The failure characteristics around shallow buried tunnels under rainfall conditions

The instability of weak surrounding rock around shallow buried tunnels induced by rainfall is a challenge for tunnel engineering and threatens construction safety. To reveal the influence of rainfall on the rock surrounding a tunnel, the results of experiments on the failure of surrounding rock under different rainfall intensities and durations using a self-developed test system are presented. First, the stress and seepage behaviors of the surrounding rock under rainfall were analysed, and the results showed that the stress increased while the pore water pressure decreased as the rainfall intensity decreased. It was more difficult to maintain vault collapse as rainfall intensity increased, and the particle erosion in the model intensified as the rainfall duration increased. The change in pore water pressure was greater than the change in stress, but the stress and pore water pressures influenced each other during rainfall. The influence of rainfall on the rock at the top of the tunnel was greater than that at the two sides of the tunnel because the seepage channels at the top of the tunnel were more developed and collapsed more easily due to smaller stresses. According to the phenomena of the surrounding rock observed during the test, the evolution of progressive failure under rainfall was roughly divided into eight stages: stability, water drop, continuous water flow, partial collapse, mud and water mixture, vault collapse, throughgoing collapse, and massive water and mud gushing. Furthermore, the final failure pattern of the surrounding rock consists of an excavation disturbance zone, vault damage zone and collapse failure zone. This research helps to reveal the progressive failure of surrounding rock around tunnels under rainfall conditions and can be used as a reference for designing disaster prevention strategies in practical engineering.