Arching effect is a common phenomenon in the systems of soil-structure interaction, and has been found to be inevitably affected by dynamic loading. The present study is devoted to investigate the evolution process of soil arch under the cyclic loading. To this end, a series of tests was conducted by using a trapdoor apparatus equipped with a cyclic loading system. By using particle image velocimetry (PIV) together with a set of dynamic load cells, evolution behaviors of the soil arch are observed and analyzed, including the geometric features, particle displacement fields and variation of vertical stresses. Based on the test results, it is found that the settlement of moving gates generates a void area over the trapdoor with a triangular boundary as the soil arch is initially formed. After applying cyclic loads, the structural boundary of the void area gradually extends vertically and moves upward to the filling surface, while the displacement region spreads in a fan-shaped patterns and extends to the sides with increasing base angles. Depending on the differences of initial trapdoor displacements and cyclic loads, two typical categories of the final stability of soil arch under cyclic loading are identified in the tests, namely the new stable cases and collapse cases. The results show that soil arch with a larger initial trapdoor displacement is more likely to experience a final collapse, as the void area extends along the filling height and a vertical slip surface is generated. The stability of soil arch under is related to the supporting effect of the accumulated soil within the void area to the lower boundary of the soil arch.
