To ensure a trouble-free operation of bulk solids sluice systems, especially lock hoppers, knowledge about the behaviour of bulk solids during and after sudden pressure changes is necessary. This paper presents the results of experimental and theoretical research. The dependence of the consolidation of bulk solids on important parameters and acting forces was determined. After a description of test plant and procedure, a model to calculate the unsteady gas flow through the bulk solid is presented. Knowing the material and process parameters, this model allows the calculation of the pressure compensation within the bulk solid due to a sudden pressure change above the surface. The vertical stress acting during pressurization can be calculated from the equilibrium of forces acting on a bulk solids volume element, provided the porosity is constant. Comparison with experimental data shows that the forces due to gas flow are responsible for the consolidation of incompressible bulk solids while compressible bulk solids are consolidated mainly by inertial forces due to bulk solids motion. Continued research shows that a simulation of the dynamic strain by a static strain is possible for incompressible bulk solids.