The origin of stress dip under the apex of a standard sandpile has stimulated significant debate within the
scientific community. On the other hand, it could be argued that a semipile built against a vertical wall is of
more practical interest since it serves as a model of dams, dykes, and embankments. There is surprisingly little
information available for the stress distribution in this case. Here we show clear experimental evidence that the
presence of the wall enhances the dip under a granular pile significantly. Our investigation provides insight into
the influence of walls on the orientation of force chains and this appears to be key in enhancing the dip.
Moreover, numerical simulations and experiments with different kinds of particles show that the vertical wall
induces an alignment of isotropic particles.