The potential for a particle to crush under one-dimensional compression is critically dependent on the coordination number of that particle. Neighboring particles decrease deviatoric forces at contacts, which reduces tensile stress and subsequent fracture propagation in the crushable particle. This phenomenon is called "shielding effect". In this paper, we model a sand particle as a spherical cluster of bonded, hexagonally packed, equally sized, non-breakable spheres with the Discrete Element Method (DEM). We use rigid walls to apply forces at the contact with neighboring particles. First, we calibrate the cluster mechanical parameters against published experimental results obtained during unconfined uniaxial compression tests. Then we propose a procedure employed in DEM to generate symmetric and random distributions of walls. We use two loading walls only: the remainder of the walls is used for passive shielding. Force-displacement curves obtained during the crushing simulations clearly show that the peak force reached when the cluster first splits increases with the number of shielding walls, which demonstrates shielding effects. The total resulting compression force applied by the walls increases linearly the coordination number. We expect that our computational method will allow the optimization of crushing in powder technology, and the prevention of crushing in geotechnical engineering.