Abstract The impact dynamic load transmission process in rectangular open tunnels subjected to falling rocks is highly complex. Considering the discrete characteristics of backfilled soils, a numerical model was established using the discrete element method (DEM) to simulate the impact process of falling rocks. The study investigates the effects of backfilled soil compactions, backfill thicknesses, and rock impact angle on the impact response characteristics of the open tunnel structure under different rockfall heights. The results indicate that: (1) The thickness of loess backfills has minimal effect on the impact force, while higher compaction results in greater impact forces; (2) When the vertical impact energy is the same, the impact angle of falling rocks has little influence on the impact load experienced by the structure, with vertical impacts representing the most unfavorable condition under the same total impact energy;(3) When the backfill thickness is small, its cushioning performance is insufficient, and the impact load on the tun? nel roof is significantly higher compared to conditions with thicker backfills; (4) When the vertical impact energy is ≤1.63 MJ, increasing the backfill thickness beyond 1.5 m does not significantly reduce the impact load on the tunnel roof, as the additional static load of the backfills outweighs the reduction in impact load. The optimal backfill thickness is related to the falling rock impact energy; for vertical impact energy ≤1.63 MJ, a backfill thickness of no less than 1.0 m is recommended.
Abstract：
The impact dynamic load transmission process in rectangular open tunnels subjected to falling rocks is highly complex. Considering the discrete characteristics of backfilled soils, a numerical model was established using the discrete element method (DEM) to simulate the impact process of falling rocks. The study investigates the effects of backfilled soil compactions, backfill thicknesses, and rock impact angle on the impact response characteristics of the open tunnel structure under different rockfall heights. The results indicate that: (1) The thickness of loess backfills has minimal effect on the impact force, while higher compaction results in greater impact forces; (2) When the vertical impact energy is the same, the impact angle of falling rocks has little influence on the impact load experienced by the structure, with vertical impacts representing the most unfavorable condition under the same total impact energy;(3) When the backfill thickness is small, its cushioning performance is insufficient, and the impact load on the tun? nel roof is significantly higher compared to conditions with thicker backfills; (4) When the vertical impact energy is ≤1.63 MJ, increasing the backfill thickness beyond 1.5 m does not significantly reduce the impact load on the tunnel roof, as the additional static load of the backfills outweighs the reduction in impact load. The optimal backfill thickness is related to the falling rock impact energy; for vertical impact energy ≤1.63 MJ, a backfill thickness of no less than 1.0 m is recommended.
SUN Zhongqiu ZHU Ming JIA FeiYang XU Yifei
.Numerical Study on the Response of Rectangular Open Cut Tunnels with Loess Backfills to the Rockfall Impact[J] MODERN TUNNELLING TECHNOLOGY, 2024,V61(6): 111-117
2024, Vol. 61 