Aluminum foam as buffer layer used in soft rock tunnel with large deformation

The squeezing deformation of surrounding rock is an important factor restricting the safe construction and long-term operation of tunnels when a tunnel passes through soft strata with high ground stress. Under such soft rock geological conditions, the large deformation of the surrounding rock can easily lead to the failure of supporting structures, including shotcrete cracks, spalling, and steel arch distortion. To improve the lining support performance during the large deformation of squeezed surrounding rock, this work selects aluminum foam with densities of 0.25 g/cm³, 0.42 g/cm³ and 0.61 g/cm³ as the buffer layer material and carries out uniaxial confined compression tests. Through the evaluation and analysis of energy absorption and the comparison of the yield pressure of aluminum foam with those of other cushioning materials and yield pressure support systems, the strength, deformation and energy absorption of aluminum foam with a density of 0.25 g/cm³ meet the yield pressure performance requirements. The numerical model of the buffer layer yielding support system is then established via the finite element analysis software ABAQUS, and the influence of the buffer layer setting on the lining support is analyzed. Compared with the conventional support scheme, the addition of an aluminum foam buffer layer can reduce the stress and deformation of the primary support and secondary lining. The maximum and minimum principal stresses of the primary support are reduced by 13% and 15%, respectively. The maximum and minimum principal stresses of the secondary lining are reduced by 15% and 12%, respectively, and the displacement deformation of the secondary lining position is reduced by 15%. In summary, the application of aluminum foam buffer layer can reduce the stress and deformation of the primary support and secondary lining, improve the stress safety of the support and reduce the deformation of the support.