An explicit dynamic material point–scaled boundary finite element coupling framework with improved hybrid contact for soil–structure interaction

Large-deformation soil–structure interaction problems involve soil distortion, evolving frictional contact, and deformable structural response, which remain challenging for conventional mesh-based approaches. This paper develops an explicit dynamic coupling framework combining the material point method with the scaled boundary finite element method. The soil domain is discretized by the generalized interpolation material point method, whereas the structural domain is represented by polygonal scaled boundary elements. For the structural solver, an explicit dynamic scaled boundary finite element formulation is established. Sector-based integration points are introduced as persistent local history points for stress update and internal-force evaluation, while consistent mass matrix is evaluated semi-analytically and converted into a lumped nodal form for central-difference integration. To model the interface interaction, a topology-aware hybrid contact algorithm uses the nearest structural boundary node only as a local search seed and treats regular surface nodes, concave and convex corners separately. Contact forces are transferred through background grid on the material point side and applied directly to the structural boundary nodes. Numerical examples reproduce structural dynamics, analytical sliding and rolling, granular collapse, and flexible retaining-wall response. The results demonstrate robust contact behaviour near evolving interfaces and corners while preserving contact-boundary resolution with a compact polygonal structural discretization.