Soil arching in ground with tunnel: Effect of distance between tunnel and trapdoor

The effects of existing tunnels on the evolution of soil arching require further investigation. In this study, trapdoor models with different distances between the trapdoor and tunnel are examined via discrete element method simulations after a numerical model is established based on experiments. The results show that as the distance between the tunnel and trapdoor (L) increases, the minimum soil arching ratio, ultimate soil arching ratio, and load recovery decrease, thus indicating that the shadowing effect of the tunnel becomes less distinctive. The essential distance affected by the tunnel is between 150 and 200 mm. The stress ratio in region L1 first decreases significantly and then gradually as the trapdoor displacement increases, reaching an ultimate value at L = 50 and 100 mm. The reverse trend is observed when L exceeds 150 mm, which is similarly observed in regions L2 and L3. The height of the equal-displacement region decreases steadily as L increases. Two distinct types of soil-arching structures are identified for interaction and independent arches. The displacement of the trapdoor increases the anisotropy of contact forces within the soil mass. The reorientation and destruction of the contact force fabric provide further insights into the formation of soil arching.