Abstract: Owing to a lack of high-energy-absorbing buffer materials, deformation of soft rock tunnels under high ground stress is severe. Therefore, a high-energy-absorbing concrete was developed using waterborne epoxy resin and emulsified asphalt as the binder material and expanded polystyrene (EPS) particles as the energy-absorbing aggregate, meeting the functional requirements of the buffer layer. The mechanical properties of this concrete under uniaxial compression were experimentally examined, and its energy absorption mechanism was elucidated through computed tomography (CT) scanning and three-dimensional reconstruction. The main findings are as follows: (1) The stressstrain curves exhibit elastic, plateau, densification, and failure stages. The plateau stress ranges from 1.189 to 1.624 MPa, the elastic modulus ranges from 17.89 to 24.50 MPa, and the ultimate compressive strain reaches 0.6. (2) The multistage energy absorption characteristics result in effective energy absorption performance of the concrete, with a maximum energy absorption per unit volume of 0.84 J/cm³, among which the plateau stage exhibits the largest proportion of energy absorption. (3) CT scanning results reveal that the deformation and energy absorption performance of the concrete are primarily determined by the densification deformation and connectivity development of EPS particles, and the skeleton structure formed by manufactured sand particles substantially improves its mechanical properties. (4) A mesoscopic deformation element based on the Gibson-Ashby porous medium model under uniaxial compression was established, and a mechanical constitutive model for the concrete was obtained.

Key words: large deformation in soft rock tunnels, high-energy-absorbing concrete, CT scanning, three-dimensional reconstruction, energy absorption mechanism, mechanical constitutive model