2D symmetric disc images of the evolution of the solid-to-gas surface density for three different versions of the nominal model where the maximum grain size was limited to 100 μm : the nominal model (top row), the nominal model with planetesimal formation but no dependency on the pressure gradient (middle row), and the nominal model without planetesimal formation (bottom row). For the sake of easy comparison purposes, images of the same simulations but without the maximum limit on the particle size were added on top of the images at 1 Myr. When the dependency on the pressure gradient is included, efficient planetesimal formation at the gap edges prevents particles from passing through the gaps, resulting in a depletion of the part of the disc that is closer to the star than the middle planet. This does not happen in the other cases, instead several bright rings are seen in the dust-to-gas ratio, and dust is also left in the innermost region of the disc.