Development of a multiscale continuous-discontinuous model and its application in blasting analysis of tunnel in calcareous sand strata

• SOIL_AND_FOAM model is implemented in Distinct Lattice Spring Model (SF-DLSM) to study blasting responses of calcareous sand. • A multiscale method coupling LS-DYNA and SF-DLSM is proposed to simulate blast wave propagation and tunnel responses. • The damage levels and critical vulnerable zones are identified for a twin-box tunnel buried in calcareous sand. Tunnels constructed in calcareous sand strata within island-reef regions are susceptible to external explosions, making accurate prediction of their dynamic responses essential for structural safety. In this work, SOIL_AND_FOAM constitutive model for calcareous sand is implemented in a continuous-discontinuous model, namely, Distinct Lattice Spring Model (DLSM), thus forming a SF-DLSM model. Then, a multiscale coupled continuous-discontinuous numerical model is developed by coupling SF-DLSM with LS-DYNA to study the blasting wave propagation and failure process of tunnel buried in calcareous sand strata. The capability and accuracy of the proposed model have been demonstrated through comparisons with analytical solutions, numerical modelling, Split Hopkinson Pressure bar (SHPB) tests and scaled field explosion tests reported in literature. Furthermore, a numerical model for a twin-box tunnel has been established to investigate the deformation patterns and damage levels under various charge weights and locations. The results reveal that the support rotation angle of the tunnel roof exhibits a power function relationship with scaled distance. Based on this relationship, tunnel damage is classified into minor, moderate, and severe levels. In addition, the damage evolution processes are simulated, with damage being found concentrated at the central wall and its connections with the roof structures. This study further advances capability of DLSM to multiscale analysis of sand-structure interaction, thus providing an efficient numerical platform for the blasting design and safety assessment of underground structures in calcareous sand strata.