<p>The construction and mining industries are producing large volumes of earthfill, rockfill and waste rock that must be safely stored. Stockpiles (or storage piles) constructed by end or push dumping are commonly used for this purpose. Such stockpiles usually have a slope angle at or near the internal friction angle of the loose cohesionless materials. However, unsaturated granular materials may show an apparent cohesion that can influence the slope angle of the storage pile and related stability conditions. In this regard, attention should be paid to the effect of water infiltration following large precipitations or rapid snowmelt, as surface recharge tends to modify the material shear strength in ways that may lead to unstable conditions. This paper investigates the effect of variable shear strength parameters and slope geometry on the stability of an unsaturated stockpile of quarry rockfill and granular soil mixture, typical of many storage facilities encountered near urban centers. Conventional limit equilibrium calculations and stability analyses with Monte Carlo simulations are carried with different parameter combinations to investigate the influence of variability on the factor of safety of an existing stockpile where an instability was observed. The analyses indicate for instance that a relatively small drop in the apparent cohesion can lead to unstable conditions similar to those identified from LiDAR measurements and observations in the field. Stability analyses are also conducted in 3D to further assess the stockpile stability and material parameters. Some of the main implications of this work for the design of surface storage piles are also discussed.</p>