关键词: 隧道工程； 落石冲击；防护结构；砂土-海绵垫层；模型试验；LS-DYNA

Abstract: Based on a tunnel entrance project, more effective rockfall impact protection structures were explored. A 1∶10 geometric similarity model test and LS-DYNA numerical calculation method were used to reveal the mechanical response mechanism of sand high-density sponge composite cushion under rockfall impact. The model test results show that the peak stress at the center of the roof belly decreases from 1.71 MPa to 0.75, 0.24 MPa with the addition of 3 and 6 cm high-density sponge to form the composite cushion, and the decrease is 55.90% and 86.43%. The results of numerical calculation equally proportional to the test show that after adding 3 and 6 cm sponges to form a composite cushion layer, the peak stress at the center of the roof belly decreases from 1.13 MPa to 0.57 and 0.22 MPa, with a decrease of 49.73% and 80.35%. The numerical calculation results of actual working conditions indicate that the stress level of the shed tunnel with composite cushion is significantly reduced, the overall stress inside the board is relatively uniform, and the stress concentration state at the center has been basically eliminated. The stress curve has changed from a broken line form of pure sand cushion to a wave like pattern, with the peak stress decreasing from 5.63 MPa to 1.77 MPa and with a reduction of up to 68.56%. The peak displacement decreases from -3.08 mm to -2.51 mm and the peak acceleration decreases from 514 m/s2 to 445 m/s2.

Key words: tunnel engineering; rockfall impact; protective structure; sand sponge cushion; model test; LS-DYNA