This work aims at developing a numerical simulation method, Soft PARticle Code (SPARC). The term textit{soft} emphasizes that no boundaries between particles are defined and every particle possesses a support consisting of a set of adjacent particles. The polynomial interpolation/approximation method is utilized for the evaluation of spatial derivatives using the information carried by particles in supports. The system of equations consisting of spatial derivatives is solved using an iterative nonlinear solver and the computation of the Jacobian matrix is parallelized. The simulations of laboratory tests have been carried out to show the applications and limitations of the current version of SPARC. In addition to the simulations, laboratory (zig-zag) model tests using fine sand were carried out, in which the cyclic tilt of a retaining wall induces a peculiar motion in the backfill (sand), with closed trajectories (eddies).