  We present an experiment which aim is to investigate the mechanical
properties of a static granular assembly. The piling is an horizontal 3D
granular layer confined in a box, we apply a localized extra force at the
surface and the spatial distribution of stresses at the bottom is obtained (the
mechanical Green's function). For different types of granular media, we observe
a linear pressure response which profile shows one peak centered at the
vertical of the point of application. The peak's width increases linearly when
increasing the depth. This green function seems to be in -at least- qualitative
agreement with predictions of elastic theory.
