Experimental and theoretical investigation on the dynamic response of foam-geopolymer sandwich cylindrical structure under long-duration plane load

Abstract

In this study, the dynamic response of the foam-geopolymer sandwich cylindrical structures (FSCS) under long-duration plane shock wave loading and the energy absorption properties of the foam-geopolymer cushion layer were investigated through model-scale blast-resistant experiments and theoretical calculations. Five FSCS models with different cushion layer thicknesses and densities were tested in a large-scale enclosed blast-resistant device. The results found that the FSCS models remained undamaged when subjected to long-duration plane wave loading with a peak pressure of 0.6 MPa and a duration of 200 ms. Increasing the cushion layer thickness enhanced pressure attenuation from 65.31 % at 15 mm to 75.71 % at 25 mm, while lower-density foam-geopolymer materials exhibited better attenuation, reaching 80.59 % at 579 kg/m³ compared to 66.36 % at 1166 kg/m³ . The top of the cylinder experienced pressure four times higher than the lateral center, with peak displacement and acceleration amplitude increasing by 60 % and 90 %, respectively. Circumferential strain was more pronounced than axial strain, while the inner wall of the lining primarily underwent elastic deformation. Furthermore, a dynamic mechanical model for underground circular tunnels under long-duration planar loading was developed, incorporating an optimal cushion layer thickness calculation method that considers material self-weight and impedance effects. This model accurately predicts the deflection variation of underground sandwich cylindrical structures at any time, providing crucial insights for the design and optimization of cushion energy-absorbing layers in sandwich structures.