  The mechanics of granular media at low liquid saturation levels remain poorly
understood. Macroscopic mechanical properties are affected by microscale forces
and processes, such as capillary forces, inter-particle friction, liquid flows,
and particle movements. An improved understanding of these microscale
mechanisms is important for a range of industrial applications and natural
phenomena (e.g. landslides). This study focuses on the transient evolution of
the tensile stress of unsaturated granular media under extension. Experimental
results suggest that the stress state of the material evolves even after
cessation of sample extension. Moreover, we observe that the packing density
strongly affects the efficiency of different processes that result in tensile
stress relaxation. By comparing the observed relaxation time scales with
published data, we conclude that tensile stress relaxation is governed by
particle rearrangement and fluid redistribution. An increased packing density
inhibits particle rearrangement and only leaves fluid redistribution as the
major process that governs tensile stress relaxation.
