In dense, static, polydisperse granular media under isotropic pressure, the probability density and the correlations of particle-wall contact forces are studied. Furthermore, the probability density functions of the populations of pressures measured with different sized circular pressure cells are examined. The questions answered are: (i) What is the number of contacts that has to be considered so that the measured pressure lies within a certain error margin from its expectation value? (ii) What is the statistics of the pressure probability density as function of the size of the pressure cell? Astonishing non-random correlations between contact forces are evidenced that lead to a rapid decay of the width of the distribution and range at least 10–15 particle diameters. Finally, an experiment is proposed to tackle and better understand this issue.
- Force and stress correlations
- Dense static granular packings
- Pressure cells
- DEM simulations