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.

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Bimsoils are a loose rock and soil system, and the occurrence of geological hazards is closely related to water. To investigate the permeability and seepage characteristics of bimsoils, factors on permeability are discussed in detail considering cementation state, and variable mass seepage is studied tentatively with selfdeveloped apparatus. Results shown that the order of factors on permeability is rock content > cementation degree > rock size > Talbot index (describing the mass percentage for different particle size of sand), and there are significant differences between factors. Besides, permeability generally increases with the increase of rock content and decreases with the increase of cementing agent content, while increases slightly due to agglomeration effect at the clay content of 8%. It is more obvious for reducing the permeability of higher rock content bimsoils by strong cementing agent, however, it tends to be same eventually with cement content increasing. The seepage of bimsoils is dominated by fine particle losses, and the secondary inrush occurs under the larger particle radius ratio. Moreover, particle losses and the time needed for secondary inrush both increase with the increase of particle radius ratio. The results would provide consults for the preparation of similar materials and the prevention of tunnels and underground engineering disasters.