Research on the self-supporting capacity of sand and pebble stratum based on tunnel model test and discrete–continuous coupling method

Self-supporting or arching effect is the important characteristic for the sand and pebble stratum. In this paper, the ultimate bearing capacity of sand and pebble stratum with different lining thickness and the failure modes of the tunnel are studied, involving the model test and discrete element methods. The numerical simulation results of the three-dimensional discrete element are verified with the test results. The research results show that increasing the lining thickness has limited impact on increasing the ultimate bearing capacity of the tunnel engineering. As the equivalent load increases, tunnels with different lining thicknesses first appear as crown failure, but the failure mode is various. It is found that tunnel excavation in the sand and pebble will cause the redistribution of the force chain. On the other hand, the numerical simulation results are basically consistent with the model test results, verifying the reliability of the numerical simulation, which can provide some important references for similar sand and pebble geological engineering cases in the future.