For block-mound construction using barges, it is important for a precise prediction of unsteady motions of settling particles with complicated flow. In this study, high-resolution calculations are implemented by LES with computational grids whose sizes are less than particle diameter. In addition, interactions between both particle-particle and fluid-particle are considered. The validity of the present model and its computational efficiency concerned with grid scale are confirmed by comparing with experimental results and several calculated simulations through behavior of fluid around a settling particle, which is measured by PIV system. An unstedy flow mechanism is exmined by comparing a calculated simulation with a experiment, which is imitated a mound construction using a barge and targeted for motions of multiple settling particles.