Simulation　of　interaction　problems　between　rock　structure　and　soil　is　a　challengeable　subject.　It　involves　a　coupled　system　that　considers　the　behaviors　of　both　rock　structure　and　soil,　together　with　interaction　between　them.　Discontinuous　deformation　analysis　(DDA)　is　suitable　for　analyzing　a　blocky　system,　such　as　rock　or　flexible　structure.　On　the　other　hand,　smoothed　particle　hydrodynamics　(SPH)　is　appropriate　for　studying　flow-like　behavior　of　soil　after　implementing　a　proper　constitutive　model.　A　coupling　scheme　that　bridges　DDA　and　SPH　can　take　advantages　of　both　methods.　Therefore,　a　numerical　method　for　such　interaction　problems　using　DDA　and　SPH　is　developed,　in　which　a　Drucker-Prager　elasto-plastic　soil　constitutive　model　is　incorporated.　In　the　developed　method,　the　interaction　between　SPH　particle　and　DDA　block　is　idealized　through　a　new　spring-dashpot　contact　model　with　the　Mohr-Coulomb　failure　criterion　used.　Several　numerical　examples　are　studied,　and　satisfactory　agreements　between　the　simulation　results　and　the　experimental　data　or　other　available　simulated　results　are　obtained,　suggesting　the　correctness　of　the　developed　method.　Further,　the　developed　method　is　applied　to　study　influence　of　backfill　on　a　masonry　arch　bridge.　Conclusively,　this　coupled　DDA-SPH　method　provides　a　potential　numerical　approach　for　studying　interaction　problems　between　rock　structure　and　soil.　©　2021　Elsevier　Ltd