Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnels

Abstract

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight. However, the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved. In this study, we propose a novel energy absorber composed of foamed concrete-filled polyethylene (FC-PE) pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compression experiments. Results show that FC-PE pipes exhibit typical three-stage deformation characteristics, comprising the elastic stage, the plastic plateau, and the densification stage. Furthermore, the plateau stress, energy absorption, and specific energy absorption of the specimens are 0.81–1.91 MPa, 164–533 J, and 1.4–3.6 J/g, respectively. As the density of the foamed concrete increases, the plateau stress and energy absorption increase significantly. Conversely, the length of the plastic plateau and energy absorption efficiency decrease. Moreover, based on the vertical slice method, progressive compression of core material, and the 6 plastic hinges deformation mechanism of the pipe wall, a theoretical calculation method for effective energy absorption is established and achieves good agreement with experimental results, which is beneficial to the optimization of the composite structure.