  Flow in soft materials encompasses a wide range of viscous, plastic and
elastic phenomena which provide challenges to modelling at the microscopic
level. To create a controlled flow, we perform falling ball viscometry tests on
packings of soft, frictionless hydrogel spheres. Systematic creep flow is found
when a controlled driving stress is applied to a sinking sphere embedded in a
packing. Here, we take the novel approach of applying an additional global
confinement stress to the packing using an external load. This has enabled us
to identify two distinct creep regimes. When confinement stress is small, the
creep rate is independent of the load imposed. For larger confinement stresses,
we find that the creep rate is set by the mechanical load acting on the
packing. In the latter regime, the creep rate depends exponentially on the
imposed stress. We can combine the two regimes via a rescaling onto a master
curve, capturing the creep rate over five orders of magnitude. Our results
indicate that bulk creep phenomena in these soft materials can be subtly
controlled using an external mechanical force.
