A micro difference blasting construction technique was employed on-site to investigate the changes in the first principal stress, vibration velocity, and displacement of the initial support structure of the lower main tunnel after the blasting construction of the upper smoke exhaust channel, in response to the construction of the main tunnel structure at a close range (4.44 m). The finite element numerical calculation method was used to quantitatively assess the safety of the adjacent tunnel. The results show that: After the full section blasting of the longitudinal exhaust duct, the most dangerous point of the initial support structure of the main tunnel is located at the arch position directly below the blasting face of the longitudinal exhaust duct. The peak vibration velocities in the X, Y, and Z directions of the control nodes are all less than the standard value of 20 cm/s, and the displacement value is within 3.63 mm; The stress and deformation curves of the lining structure peak within 200 ~ 300 ms and subsequently exhibit oscillatory attenuation over time. The local tensile stress concentration state is formed at the arch crown, and the overall risk of the structure is controllable. After using the micro difference blasting technology for construction on site, the smoke exhaust channel smoothly crossed through the main tunnel structure. At the intersection of the initial support arch crown, there was a local phenomenon of initial support falling off due to individual anchor rod bending and prying, and the overall stress was relatively safe. The on-site monitoring results are consistent with the numerical calculations, proving the reasonable reliability of the micro difference blasting construction technology. The research results can provide reference for similar projects.

In order to find a more effective energy dissipation and vibration reduction shed tunnel structure, this study uses model tests and LS-DYNA numerical calculation methods to explore the mechanical response mechanism of shed tunnel structure with pure sand cushion and sand EPE composite cushion under the impact of falling ball. Through research, it is concluded that the peak strain at the center of the top plate abdomen under the pure sand cushion is 48.78×10^-6, the peak stress is 1.46 MPa, close to its ultimate tensile strength of 1.78 MPa. After adding 6 cm thick EPE cushion, the peak strain can be reduced by 83.42%, the equivalent stress can be reduced to 0.24 MPa, and the safety factor can reach 7.42. When the thickness of EPE cushion is increased from 0 cm to 4 cm, the strain reduction at Z1 and Z2 characteristic positions can reach 57.14% and 65.22% respectively. When the thickness of EPE cushion is increased from 4 cm to 6 cm, the strain reduction at Z1 and Z2 positions is 19.05% and 18.75% respectively. When the thickness of EPE cushion is set to 4 cm, the vibration reduction effect reaches the inflection point. Build a numerical calculation model with the size of 1:1 with the model test. After adding 2, 4, and 6 cm thick EPE cushion, the central stress of the roof abdomen decreases from 1.16 MPa to 0.699, 0.418, and 0.313 MPa, with a decrease of 39.74%, 63.96%, and 73.02%. It is recommended that the actual protective structure should be equipped with 40~60 cm thick EPE cushion. The calculation model of the actual shed tunnel on site was established. After the 40 cm thick EPE cushion was added, the peak stress of the central unit decreased from 5.71 MPa to 1.72 MPa, with a decrease of 69.88%, and the peak ball fall acceleration decreased from 546 m/s² to 432 m/s², with a decrease of 20.88%. It was verified that the sand EPE composite cushion can play an obvious protective role on the shed tunnel structure.

In order to explore a more safe and effective slope rockfall protection structure, this study is based on the numerical calculation of SPH-FEM coupled dynamics and the 1∶10 geometric similarity indoor model test, aiming at the vibration reduction mechanism of the "sand-foamed rubber" composite cushion shed tunnel. The results show, when the falling rock is impacted at the speed of 20 m/s, the peak stress of the central unit of the roof abdomen can reach 2.89 MPa, which exceeds the ultimate tensile strength of C30 concrete by 2.01 MPa. After adding 0.2, 0.4, 0.6, 0.8, and 1.0 m foam rubber cushion, the peak stress of the central unit is 2.36, 1.12, 0.79, 0.65, and 0.58 MPa, which is 18.34%, 61.25%, 72.66%, 77.51%, and 79.93% lower than that of the pure sand cushion. Add 2, 4 and 6 cm thick rubber cushion at the longitudinal measuring point P1 on the roof belly of the shed during the test, and the peak strain is 50.57 με. It dropped to 27.17, 15.22 and 10.36 με respectively. The decrease was 46.27%, 69.90% and 79.51%. For the transverse test position T1 of the roof abdomen, the peak strain under the composite cushion condition is 48.47 με to 26.54, 17.29, 13.59 με. The composite cushion can significantly reduce the impact energy of rockfall and the stress level of the roof. The model test and numerical calculation results are basically consistent. The suitable thickness for on-site setting of foam rubber under this working condition is 0.4~0.6 m. The research results can provide reference and reference for relevant protective engineering design.